electrical safety principles hazards & risks

Section 1

of 181

Last Updated 02/02/2016

ELECTRICAL SAFETY PRINCIPLES,

HAZARDS & RISKS

PURPOSE:

In this topic you will analyse safety principles to which electrical systems in building and

premises shall comply.

TO ACHIEVE THE PURPOSE OF THIS SECTION:

At the end of this section the student will be able to:

Discuss safety principles as given in Part 1 (Section 1) of the Wiring Rules AS/NZS3000 with deemed-to-comply requirements given in Sections 2 to 8.

List the various compliant methods for providing protection of an electrical installation.

Define the term “direct contact”

Provide examples of where and how a direct contact with live parts may occur in anelectrical installation

Provide examples of where and how an indirect contact with conductive parts mayoccur in an electrical installation

Discuss the requirements and need for an installation to comply with design andselection of equipment

List the factors influencing the severity of an electric shock and describe the effects ofcurrent flowing through a human body

Describe the thermal effects of current and the hazards of overload current, faultcurrent, arcing and poor electrical connections

Describe the effect of installing cables in groups

List the precautions to be taken to protect electrical installations, structural andassociated materials and persons from burns produced by heat in electrical equipment

Explain how the fire (rating) integrity of a structure shall be maintained in relation to theelectrical installation

Describe the hazards associated with mechanical movement associated with electricmotors and the measures taken to mitigate the hazard

REFERENCES:

Electrical Wiring Practice. 6th Edition. Petherbridge K & Neeson I, Volume 1

Electrotechnology Practice. 1st Edition. Hampson J

AS/NZS3000:2007

Section 1 – Safety, hazards & risks

of 181


Version 1

1. PURPOSE OF THE WIRING RULES

Refer to clause - Scope:

The 2007 edition of the Wiring rules AS/NZS 3000 establishes the safety requirements

for the

______________________________

______________________________

______________________________ of electrical installations,

including the selection and installation of equipment forming part of such electrical

installations.

The requirements are intended to protect -

______________________________

______________________________

______________________________ from electric shock, fire and physical injury.

2. APPLICATION OF THE RULES

Refer to clause - Application:

The principal application of the Wiring Rules relates to electrical installations in -

______________________________________________________________________

______________________________________________________________________

______________________________________________________________________

______________________________________________________________________

Electrical work is to comply with sections 2-8 of the AS/NZS3000 standard, and any

other relevant standard or code of practice that may pertain to any particular installation.

3. DEFINITIONS

Refer to clause - Definitions:

In order for the Wiring Rules to be understood and interpreted correctly, it is necessary

to gain a clear understanding of specific terms related to electrical wiring.

The purpose of clause 1.4 is to provide a set of definitions that provide a precise

explanation of a various terms used in conjunction with an electrical installation. If at any

time you encounter a term or word related to an electrical installation with which you are

unfamiliar, you should refer to the appropriate part of clause 1.4 for clarification.


of 181


4. FUNDAMENTAL PRICIPLES

AS/NZS 3000 establishes a set of fundamental principles in order to provide protection

for safety.

Refer to clause - Protection against dangers and damage:

In electrical installations the three major types of risk are -

___________________________ - arising from contact with parts which are live in

normal service (direct contact) or parts which

become live under fault conditions (indirect

contact).

___________________________ - likely to cause burns, fires and other injurious

effects.

___________________________- equipment installed in areas where explosive

gases or dusts may be present

5. BASIC PROTECTION - (PROTECTION AGAINST DIRECT CONTACT)

Refer to clause 1.4.34 – Contact, direct:

Direct contact occurs when a person contacts a conductor or conductive part that is –

_____________________________________________________________________

Figure 1


of 181


Refer to clause 1.5.4.1 - General:

Protection against direct contact may be provided by various means, all of which are

intended to provide protection against dangers that may arise from contact with parts of

an electrical installation that are –

________________________________________________________________

Refer to clause 1.5.4.2 – Methods of Protection:

Protection against direct contact with live parts shall be provided by one or any

combination of the following methods -

________________________________________________________________

________________________________________________________________

________________________________________________________________

________________________________________________________________

Refer to clause 1.5.4.3 - Protection by insulation:

Live parts shall be completely covered with insulation capable of withstanding the

mechanical, chemical, electrical and thermal influences to which it may be subjected in

service.

Does paint, enamel or varnishes provide adequate protection against direct contact?

___________________________________________________________________

Refer to clause 1.5.4.4 - Protection by barriers or enclosures:

Where barriers or enclosures protect live parts, the degree of protection afforded shall

be at least -

________________________________________________________________

________________________________________________________________

The removal of doors, lids and covers from an enclosure shall not be possible unless -

________________________________________________________________

________________________________________________________________

________________________________________________________________


of 181


Version 1

Refer to clause 1.5.4.5 - Protection by obstacles:

Obstacles are intended to prevent

________________________

contact with live parts but not

______________________

contact by deliberate

circumvention of the obstacle.

Figure 2

Refer to clause 1.5.4.6 - Protection by placing out of reach:

Simultaneously accessible parts at different voltages shall not be within arm's reach.

If two parts are said to be simultaneously accessible, they are not more than _________

metres apart.

Refer to clause 1.4.12 - Arm's reach:

Arms reach is defined as:

The limit a person can _________________ without assistance, from any point on a

surface where persons usually _________________ or _______________________.

The limit of arms reach -

above a surface is

____________ metres

adjacent to a surface is

____________ metres

below a surface is

____________ metres.

Figure 3


of 181


Version 1

6. FAULT PROTECTION - (PROTECTION AGAINST INDIRECT CONTACT)

Refer to clause 1.5.5.1 - Protection against indirect contact:

The Rules require that protection shall be provided against ___________________that may arise from contact with exposed conductive parts which may become live –

_____________________________________ (indirect contact).

Refer to clause 1.4.35 - Contact, indirect:

Indirect contact is contact with a conductive part which is -

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

Figure 4

Refer to clause 1.5.5.2 - Methods of protection:

The methods of protecting against indirect contact are -

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

The most commonly used method to protect against indirect contact is:

_____________________________________.

Protection against indirect contact is expanded in further sections of this workbook.


of 181


Version 1

7. EQUIPMENT CLASSES

Equipment is classified as Class I, Class II or Class III in accordance with the method of

protection used to prevent electric shock.

Refer to clause 1.4.27 - Class I equipment:

Class I - denotes equipment where protection against electric shock is afforded by

basic insulation between live parts and exposed conductive parts, the

exposed conductive parts being connected to a protective earthing

conductor so the circuit protective device will operate to disconnect supply

if the basic insulation fails. For example a switch in a metal enclosure; an

appliance with a metal enclosure such as a washing machine.

Refer to clause 1.4.28 - Class II equipment:

Class II - denotes equipment where shock protection is afforded by the provision of

double insulation or reinforced insulation between live parts and

accessible conductive parts, and having no provision for protective

earthing of those conductive parts. This class of equipment shall be

marked with the symbol for Class II.

Refer to clause 1.4.29 - Class III equipment

Class III - protection from shock relies on the supply voltage and any internally

generated voltage being not greater than Separated Extra-Low Voltage

(SELV) which at no load will not exceed 50 V between conductors.

clause 1.4.83 - SELV is a supply which may be isolated from the supply

mains or where supply from the mains is through a safety isolating

transformer or converter with a separate winding.

Table 1 shows the identifying symbols for the three equipment classes.

Table 1

Equipment Class

Protective Measures

Symbol

I Basic insulation + protective earth

II Basic insulation + supplementary insulation or reinforced insulation

III Separated extra-low voltage (SELV)


of 181


Version 1

8. HAZARDS - INADEQUATE PROTECTION or poor practices

By far the biggest risk of injury occurring from performing electrical work is electric

shock. Further hazards exist and are covered in later parts of this workbook.

As electricians, we are all bound to make sure every job is compliant with all relevant

Standards, Codes and Regulations. The safety and integrity of work performed must

remain intact for many years after the initial installation.

Remember, AS/NZS3000 may be applied through legislative requirements, made

in each State and Territory of Australia and in New Zealand, concerned with the

safety of electrical installations. It may be used in court. Non-compliant and unsafe

work or work practices can see us made personally liable for injury or death to

persons and/or damage to property and equipment.

ELECTRIC SHOCK

There are three ways in which electric shock might be directly fatal -

respiratory arrest

asphyxia

ventricular fibrillation

The severity of electric shock depends on the -

____________________________________________

____________________________________________

____________________________________________.

When a person experiences an electric shock, they are first exposed to a -

“touch voltage”, that results in a

“touch current”.

Refer to clause 1.4.95 - Touch voltage:

A touch voltage is a voltage –

_____________________________________________________________________

_____________________________________________________________________

Refer to clause 1.4.94 - Touch current:

A touch current is a current –

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________


of 181


Version 1

Figure 5 and table 1 show approximate impedance values for various current paths

through the human body.

Exercise 1:

Using the impedance values listed in table 1, with a touch voltage of 230V; calculate the

touch current for each pathway.

Table 1

Current Path

Impedance ohms

Hand to hand 1000

Hand to foot 1000

Hand to both feet 750

Hand to seat 500

Both hands to seat 250

Pathway Calculation Touch Current

Hand to hand

Hand to foot

Hand to both feet

Hand to seat

Both hands to seat

Figure 5


of 181


Version 1

The time-current effects on the human body are shown in figure 6 and have been

accepted as the international standard for the development of techniques of protection

against electric shock.

Figure 6

The characteristic curves a, b and c1 form the boundaries of four zones representing the

various time-current effects on the human body. (p58, Vol. 2, Electrical Wiring Practice)

Table 2

Zone Physiological Effect

1 usually no reaction

2 usually no harmful physiological effects

3

usually no organic damage

likelihood of muscular contractions and difficulty in breathing

possibility of cardiac arrest, increasing with value of current and time

4

including the effects of zone 3, and:

c1 probability of ventricular fibrillation increased to 5%

c2 probability of ventricular fibrillation increased to 50%

c3 probability of ventricular fibrillation increased to above 50%

further increases in current and time is likely to cause arrest andsevere burns


of 181


Version 1

Exercise 2:

For a touch current of 200mA, what would be the likely physiological effect for each of

the duration’s shown below?

Table 3

Duration of Current Flow

Zone Physiological Effect

20mS

100mS

500mS

1S

2S

Exercise 3:

Curve b is the division between zones 2 and 3. For a touch current of 20mA, how long

would it take for the body to cross the division and enter zone 3 and what would be the

impedance of the body when the touch voltage is 230V?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

Figure 7


of 181


Version 1

9. PROTECTION FROM EXCESSIVE TEMPERATURES

A major effect of current flow is the production of heat. The quantity of heat produced is

given by the equation -

H = I2.R.t

where: H = heat produced in joules

I = current in amperes

R= the resistance of the current path

t = the duration of current flow in seconds

The heat produced is proportional to the square of the current.

What is the effect on the heat produced, if the current in a conductor is doubled?

__________________________________________________________________

Refer to clause 1.5.8 - Protection against thermal effects in normal service:

Electrical installations shall be arranged so that there is no risk of ignition of flammable

materials because of -

_____________________________ or

_____________________________ in normal service.

During normal operation of the electrical equipment there shall be no risk of ________

or livestock suffering _________.

NOTE: ambient air temperatures should be considered when installing cable and equipment.

Refer to clause 4.2.1 – protection against thermal effects - general:

The selection and installation of _________________________ shall be such that the

temperature characteristics of the electrical equipment, properly installed and operated,

do not adversely affect the electrical equipment, the electrical installation itself, or any

other installation, whether electrical or not.


of 181


Version 1

10. HAZARDS FROM EXCESSIVE TEMPERATURES

Excessive temperatures may cause ignition of flammable materials, and can cause

injury and damage by contact burns, the spread of fire and explosion.

Refer to clause 1.5.12 – Protection against the spread of fire:

Where a wiring system passes through a wall, floor or ceiling, what should be

maintained? __________________________________________________________

_____________________________________________________________________

Figure 8 Figure 9

Refer to clause 3.7.2.3 - Loosening of connections:

Connections shall be made so that _______________________________ is likely due

to vibration, alteration of materials or temperature variations to which the connections

are likely to be subjected in normal service. Loosening of connections may lead to

arcing, fire and explosion.

When a number of cables from various circuits are

grouped or bundled together, then mutual heating will

result. For example the cables laid on a cable tray,

see figure 9.

The increased heat is detrimental to the cables'

insulation.

In order to protect the insulation of each cable, it is

necessary to derate the current carrying capacity of

the various circuits bundled together.

Figure 10


of 181


Version 1

Refer to clause 4.2.2.3 – Protection from high temperatures:

Provision shall be made against the effects of:

_____________________________ (as a result of direct contact), and;

_____________________________ (air temperature rise)

Note 2 of clause 4.2.2.3 states that lamps and ballasts etc. are examples of high

temperature sources. Down lights and recessed luminaires require adequate area in

the roof space to allow heat to dissipate or they can start a fire.

Refer to clause 4.5.2.3 and Figure 4.7 for fire safety regarding recessed luminaires

The above diagram is an extract from AS/NZS 3000:2007. It indicates the default

clearance of recessed luminaires. In some cases the manufacturers’ specifications will

allow these clearances to be reduced.

Refer to clause 4.5.2.2 – Lamps near flammable materials

As protection shall be made against the effects of radiating heat, care must be

taken not to place lamps near flammable objects. Common situations include

lamps that highlight walls or paintings etc.

Refer to table 4.2

What is the minimum default distance a 500 W directional shop-lighter fitting

should be from the front edge of a book rack in a department store? _________


of 181


Version 1

11. PROTECTION AGAINST OVERCURRENT

Refer to clause 1.5.9 - Protection against overcurrent:

Protection against overcurrent may be provided by -

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

An overcurrent is a current that exceeds a particular rated value. An Overcurrent may

occur in a circuit as a result of:

______________________________

______________________________

Refer to clause 1.4.37 - Current, fault:

A fault current is defined as a current resulting from an __________________________

or from the bridging of ______________________________.

Refer to clause 1.4.38 - Current, overload:

An overload current is defined as an ________________________________________

_____________________________________________________________________.

Refer to clause 1.4.39 - Current, short-circuit:

A short-circuit is defined a fault current arising from _____________________________

_____________________________________________________________________.

Refer to clause 1.5.10 - Protection against earth fault currents:

Protective earthing conductors and any other parts intended to carry an earth fault

current shall be capable of carrying that current without attaining -

______________________________________________________________________


of 181


Version 1

12. PROTECTION AGAINST OVERVOLTAGE

Refer to clause 2.7.1 - Protection against overvoltage - general:

Overvoltage may occur in an installation as a result of:

________________________________________________________________

____________________________________

____________________________________

____________________________________

Protection against overvoltage may be achieved by:

____________________________________

____________________________________

A common method to protect circuits and equipment from the undesirable effects of

overvoltage is to install ________________________________________ (S.P.D’s)

13. PROTECTION AGAINST MECHANICAL HAZARDS

Refer to clause 1.5.13 - Protection against injury from mechanical movement:

Protection shall be provided against injury from mechanical movement of electrically

actuated equipment, where -

________________________________________________________________

________________________________________________________________

Electric motors shall be provided with suitable devices for –

_____________________________________________________________________

Figure 12 Figure 13 Figure 14

Name a possible cause of automatic motor restarting and reversal that must be

protected against.

_____________________________________________________________________


of 181


Version 1

14. INSTALLATION DESIGN REQUIREMENTS

In order for an electrical installation to function in a safe and practical manner, it must be

designed to meet the minimum safety requirements set out in AS/NZS3000 and any

other relevant Australian Standard, Regulation or Code of Practice (COP) for the

particular installation type.

Refer to Section 1, Clause 1.6 of AS/NZS3000 and complete the following:

An electrical installation shall be designed to:

a) protect ___________, ___________ and ___________from harmful effects;

b) function _____________ as intended;

c) connect, __________ _________ and be _____________ with the electricity

distribution system, or other source of supply, to which the electrical

installation is to be connected;

d) minimize ________________ in the event of a fault; and

e) facilitate __________ operation, inspection, testing and _________________.

In order to meet the requirements of clause 1.6, we need an understanding of the

supply to which load will be connected, the maximum demand of individual load

devices and installations as a whole, and the way in which load is divided into

circuits.

15. SUPPLY CHARCTERISTICS

The electrical equipment and the wiring systems installed must be compatible with the

characteristics of the supply network. Most installations are supplied by electrical

distributors such as Ausgrid or Endeavour Energy. However it is not uncommon for

private supply sources to be in use. In remote areas solar, wind and small internal

combustion generators are common.

The nominal voltage for supply in Australia is ______/ ______V, generated at _____Hz.

Countries such as the United States use a 110 V 60 Hz system. Equipment to suit

the American supply will not be compatible with Australia’s 230 V 50 Hz system.

Refer to clause 1.6.2 – Supply characteristics:

Read clause 1.6.2 parts (a) to (i) regarding characteristics of the electricity supply

which need to be determined.

Use group discussion to answer the questions relating to parts (a) to (i) on the

following page.


of 181


Version 1

(a) Generally the supply in Australia is A.C or D.C? ______________________

(b) The number of supply phases connected / permitted will depend on the

maximum demand and load types. Phases permitted will generally be:

- Installations with a maximum demand less than 100A _________________

- Installations exceeding 100A or with 3 phase equipment _______________

(Note: 3 phase supply is not always available. The NSW Service and Installation Rules gives guidance on the number of phases permitted to be connected)

(c) The nominal supply voltage in Australia is _______ / _______ volts

Not 240/415 Volts.

- Voltage should not rise above: ______% ( _______ / _______ V)

- Voltage should not fall below: ______% ( _______ / _______ V)

(d) The standard generated frequency in Australia is _________ Hz.

(e) The maximum current that is supplied to the installation can be set to limit at the

electricity distributors discretion.

(f) The prospective short circuit current is the maximum possible current that could

flow under short circuit conditions. Protection devices must be capable of safely

and adequately interrupting this current without damage.

(g) The ________ earthing system is used for protection in Australia.

(h) Limits on the use of equipment. Care should be when installing load devices

such as motors which can draw large currents during starting. Equipment is not

permitted to distort the supply voltage or frequency.

(i) Harmonic current or other limitations. Modern electronic equipment such as

P.C’s, inverters, electronic ballasts and variable speed drives cause harmonics.

Harmonics can cause transformers and neutral conductors to ______________.

16. MAXIMUM DEMAND - overview

Consumers mains, submains and other electrical equipment of an electrical installation

shall be designed and installed to meet the maximum demand requirement of clauses

1.6.3 and clause 2.2.2.

Maximum demand is the highest current expected to flow in a conductor at any given

time. It is not necessarily the total of the connected load on the conductor.

AS/NZS3000 allows for “diversity” in the calculation of maximum demand for domestic

installations. Diversity means that allowances have been made for the expected current

in the circuit as not all load is considered to be on at the same time. For example, a

power circuit may have 20 outlets with only 12 actually used, or a cook-top has 4

elements, but it is not expected that they all be set to high or all on all the same time.


of 181


Version 1

Refer to clause 2.2.2 – Maximum demand:

The 4 methods permitted to be used in the determination of maximum demand:

_______________________

_______________________

_______________________

_______________________

If the actual measured maximum demand is found to exceed that obtained by

calculation or assessment, which value should be used?

_______________________

.

Maximum demand will be covered in depth in further units of study.

17. VOLTAGE DROP CONSIDERATIONS

As discussed earlier in this section, the nominal supply voltage for Australian

installations is _______ / _______ V with a tolerance of +10% and – 6%.

Therefore the voltage at the terminals of energy consuming equipment (load) should not

fall below ________ V for single phase, or ________V for 3 phase.

Installations need to be designed so as the collective or total voltage drop across all

parts of a circuit (mains, sub-mains and final sub-circuits) is not to high so as to limit the

remaining voltage at the equipment terminals.

This percentage of voltage drop is spread across the whole installation, from the point of

supply to the load. It is not applied separately to consumer’s main, sub-main and final

sub-circuit. See figure 15.

Figure 15

As discussed in earlier units of study, voltage drops occur in electric circuits as work is

done overcoming the resistance of the cable. Cable resistance is the opposition to

current flow.

In A.C. circuits, opposition to current flow occurs because of cable resistance and circuit

reactance. This "total" opposition is known as _________________.

Main Switch

Board

Sub Dist

Board

Consumers

Mains

Sub

MainsLoad

Final

Sub-CircuitMain Switch

Board

Sub Dist

Board

Consumers

Mains

Sub

MainsLoad

Final

Sub-Circuitpoint of

supply


of 181


Version 1

3 V 3.5 V 4 V

Main Switch

BoardLoad

Sub Dist

Board

Consumers

MainsSub

Mains

Final

Sub-Circuit

3 V 3.5 V 4 V

Main Switch

BoardLoad

Sub Dist

Board

Consumers

MainsSub

Mains

Final

Sub-Circuit

Voltage drop in an AC circuit can be determined by Vd = IZ.

It can be seen by the equation that if I is increased, voltage drop will ___________.

It can also be determined that if Z is increased, voltage drop will ____________.

As current is generally fixed by the impedance of the connected load, the resistance of

the cable is all that can be altered. Long runs of cable anywhere in the installation will

cause the voltage drop to increase toward the permissible amount.

Under-voltage can cause electric motors to overheat and fail and render some electronic

devices inoperable. A simple solution to the problem is to increase cable size.

AS/NZS clause __________ covers requirements for Voltage Drop.

Exercise 4:

Figure 16 is a 230 V single phase installation.

(a) Determine the total conductor voltage drop. _______V

(b) Does the circuit comply with Australian standards (yes/No) why? _______

_____________________________________________________________

Figure 16

Exercise 5:

Figure 17 is a 400 V three phase installation.

(a) Determine the total conductor voltage drop. _______V

(b) Does the circuit comply with Australian standards (yes/No) why? _______

_____________________________________________________________

Figure 17


of 181


Version 1

Main Switch

Board

Consumers

MainsLoad

Final

Sub-Circuit

Vd = 22 V Vp = ? V

Main Switch

Board

Consumers

MainsLoad

Final

Sub-Circuit

Vd = 22 V Vp = ? V

Exercise 6:

Figure 18 is a 400 V three phase installation.

(a) Determine the total permissible voltage drop on the final sub-circuit conductor.

_______________________________________________________________

_______________________________________________________________

Figure 18

An in depth analysis of Voltage Drop will be covered in further units of study.

18. ARRANGEMENT OF CIRCUITS.

To satisfy the design requirements AS/NZS3000, it is necessary to split the installation

into a number of circuits. It was noted earlier that reducing the current drawn by a circuit,

we can also reduce the voltage drop across the circuit conductor(s). (V=IZ).

Refer to clause 1.6.5 – Electrical Installation Circuit Arrangement

Arranging installations into circuits:

provides minimised _________________ in the event of a fault,

and facilitates;

___________________________

___________________________

___________________________

___________________________

Circuit arrangements and control will be expanded in section 2 of this workbook.

******************************


of 181


Version 1

*****************NOTES****************

NAME: Practical 1

of 181


Version 1


HAZARDS & RISKS

There is no practical session for this topic.

– REMEMBER –

– WORK SAFELY AT ALL TIMES –

Observe correct isolation procedures

Practical 1 - Safety, hazards & risks

of 181


Version 1

************* NOTES *************

.

Section 2

Page 1 of 181


Version 1 UEENEEG063A S2 – Cct.&Control Arrangement


HAZARDS & RISKS

The following questions require reference to AS/NZS 3000:2007 Wiring Rules. Please

write the answer to the questions in your own words and quote the relevant clause

number.

1. What is the scope of AS/NZS 3000:2007?

_________________________________________________________________

_________________________________________________________________

_________________________________________________________________

_________________________________ AS/NZS 3000 reference ____________

2. Do the requirements of AS/NZS 3000:2007 apply in each state and territory ofAustralia?

_________________________________________________________________

_________________________________ AS/NZS 3000 reference ____________

3. What is meant by the term “readily accessible”?

_________________________________________________________________

_________________________________________________________________

_________________________________________________________________

_________________________________ AS/NZS 3000 reference ____________

4. What is meant by the term “arms reach” and what are the limits of arms reach?

_________________________________________________________________

_________________________________________________________________

_________________________________________________________________

_________________________________ AS/NZS 3000 reference ____________

5. What level of insulation applies to Class I equipment?

_________________________________________________________________

_________________________________ AS/NZS 3000 reference ____________

6. What is direct contact?

_________________________________________________________________

_________________________________ AS/NZS 3000 reference ____________

S2 – Cct. & Control Arrangement

Page 2 of 181



7. A person receives an electric shock from the metal frame of an electric motor.According to AS/NZS 3000:2007, what is the name given to this type of contact?

_________________________________ AS/NZS 3000 reference ____________

8. A circuit does not have an electrical fault, but draws excessive current. What is thename given to this current?

_________________________________ AS/NZS 3000 reference ____________

9. What is the definition of an obstacle?

_________________________________________________________________

_________________________________ AS/NZS 3000 reference ____________

10. Describe the meaning of the term “touch voltage”.

_________________________________________________________________

_________________________________ AS/NZS 3000 reference ____________

11. What is meant by the term “touch current”?

_________________________________________________________________

_________________________________________________________________

_________________________________ AS/NZS 3000 reference ____________

12. List the three major types of risk in an electrical installation as identified byAS/NZS 3000:2007.

_________________________________________________________________

_________________________________________________________________

_________________________________ AS/NZS 3000 reference ____________

13. If a “touch voltage” exceeds certain values a protective device must disconnectthe supply. What are the limits of “touch voltage”?

_________________________________________________________________

_________________________________ AS/NZS 3000 reference ____________

14. When protection against indirect contact is provided by automatic disconnection ofthe supply, what is the maximum disconnection time for –

a) a power circuit with a rating of less than 63Ab) equipment that has only single insulationc) an electric ranged) a submain.

(a)___________________(b)___________________(c)_____________________

(d)_______________________________ AS/NZS 3000 reference ____________


Page 3 of 181



15. Using the time-current curves of figure 1, for a duration of 500mS, what zones

would result for a body current of –

a) 20mA

b) 200mA

(a)_______________________________________

(b)_______________________________________

16. Using the time-current curves of figure 1, for a body current of 20mA, identify the

zone and the physiological effect that would result for the following time periods –

a) 20mS

b) 200mS

c) 2,000mS

(a)_____________________________________________________________

(b)_____________________________________________________________

(c)_____________________________________________________________

Figure 1


Page 4 of 181



CIRCUIT AND CONTROL ARRANGEMENT

PURPOSE:

In this topic you will analyse electrical circuits and control arrangements for typical

electrical installations and determine the necessity to separate electrical equipment

and load devices into circuits for safety, protection and practical purposes.



State reasons for dividing electrical installations into circuits

Discuss the factors that shall be considered in determining the

number and type of circuits required for an installation.

Calculate daily and seasonal demand for lighting power, heating

and other loads in a given installation.

Determine the number and types of circuits required for a particular

installation.

Analyse diagrams/schedules of circuits for given installations.

Determine application and arrangements of SELV and PELV

circuits

Determine application and arrangement of an isolated supply

REFERENCES:

Hampson, J. Electrotechnology Practice, Pearson Education,

Frenchs Forest NSW. Pages 97 - 99

AS/NZS 3000:2007


Page 5 of 181



INTRODUCTION

Electrical installations widely vary from basic, low demand installations such as granny

flats and domestic homes, to complex, high demand installations such as commercial

buildings or industrial factories to name just a few.

It is simply not practical to place the entire electrical load from any of the above

installations onto a single circuit, therefore electrical design and layout must be

considered prior to commencing work.

Electrical design is an integral skill that an electrician requires in order to install

electrical cables and equipment in a safe and reliable manner and to meet mandatory

safety requirements and customer specifications.

Design skills also allow for accurate quotations of work to be performed, accurate

stock orders, ease of logistics and cost effectiveness

ELECTRICAL INSTALLATION DESIGN

As discussed in the previous section, for an electrical installation to function in a safe

and practical manner, it must be designed to meet the minimum safety requirements

set out in AS/NZS3000 and any other relevant Australian Standard or Code of Practice

(COP) for the particular installation type.

Clause 1.6 of AS/NZS3000 sets out 6 fundamental design requirements that

installations must comply with.

Breaking our installations down and separating load groups into a number of circuits

helps achieve the requirements of clause 1.6.

ARRANGEMENT INTO CIRCUITS

To satisfy the design requirements and Clause 1.6 of AS/NZS3000, it is necessary to

split the installation into a number of circuits.

Circuits can be classified into 3 broad groups:

____________________________ - used to connect the entire installation to

the street supply at only one point for ease of isolation.

____________________________ - used to connect between switchboards;

no load is connected directly to this cable.

____________________________ - used to connect the load to the

main switch board or distribution / sub-board.


Page 6 of 181



Figure 1 below is an extract from AS/NZS3000:2007, Appendix B. It highlights 3 levels

of circuits; Supply to the Main Switchboard (the mains), Submains and Final

Subcircuits.

Figure 1

Figure 2 below shows a simplified block diagram of a typical domestic arrangement

whereas figure 3 shows the typical arrangement for a commercial or industrial

installation.

Figure 2

Figure 3


Page 7 of 181



Refer to Section 1, Clause 1.6.5 of AS/NZS3000 and complete the following:

Every electrical installation shall be divided into circuits as necessary to avoid

____________ and minimize ________________ in the event of a fault.

Furthermore, installations are divided into circuits to:

f

acilitate __________ _____________,

a

llow full and thorough ____________ and ____________

a

llow for ongoing repair and _________________.

It is the responsibility of the electrician to determine how the circuits will be separated.

Many factors need to be considered when determining the circuit arrangements. Listed

below are some examples:

D

oes the load need to be on a designated circuit. ie: a circuit of its own

C

an the load be on a common circuit with other devices. ie a mixed circuit

H

ow many socket outlets can be connected to a single circuit

A

re socket outlet circuits designed to avoid nuisance tripping or overload

H

ow many light points can be connected to a single circuit

W

hat can be deemed as a light point

H

ow many RCDs are required depending on the final subcircuit arrangement

W

hat is the current demand going to be on each circuit

W

hat size cable will the circuit need to be wired in

W

ill voltage drop be a problem based on length and/or circuit demand


Page 8 of 181



H

ow will the circuit be protected

W

here will be the circuit originate. ie: Main switchboard or DB etc.

H

ow will the separated circuits be balanced across multiple phases

A

re the minimum conditions of clause 1.6 met

Refer to Clause 2.2 – Arrangement of Electrical Installation

Complete the following 3 exercises:

Exercise 1:

Read Clause 2.2.1.1 and discuss the above list as a class group. Can you determine 2

more examples of what else may need to be considered when designing an

installation and separating circuits.

______________________________________________________

___

______________________________________________________

___


Page 9 of 181



Exercise 2:

List 6 Load groups that are typically divided into separate final sub-circuits:

__________________________________

__________________________________

__________________________________

__________________________________

__________________________________

__________________________________

Exercise 3:

Which Appendix in AS/NZS3000 can be referred to seek recommended circuit

arrangements for basic installations?

Appendix ______. Table 1 in this appendix indicates different load

groups

Once the load is appropriately separated into circuits a suitable circuit protection

device and cable can be selected for each circuit. The protection device which is

typically a circuit breaker or HRC fuse is selected to allow supply the load and to

protect the circuit conductors. For some circuits, the ‘additional’ protection of a

___________ ____________ ____________ will also be required.

The current in a circuit must not exceed the current rating of the circuit protective

device. The cable size is to have a current rating equal to or larger than the circuit

protective device selected.

The type of cable used should suit the environment in which is to be installed. In most

cases Thermo Plastic Sheathed (T.P.S) cables are commonly used as they are cost

effective and easily installed.

The number of points per final sub-circuit varies from one single point to many. In

industrial and commercial installations the number of points is restricted to ensure

correct operation of the circuit and avoid nuisance tripping. AS/NZS 3000 Appendix C

(T. C8) gives guidance to the number of points per final subcircuit.

In domestic installations “diversity” is applied to the circuits to allow the number of

points to be increased to reduce costs and make wiring more practical. Diversity

means that allowances have been made for the expected current in the circuit as not

all load is considered to be on at the same time.


Page 10 of 181



DETEMINING MAXIMUM DEMAND FOR FINAL SUB-CIRCUITS

Maximum demand is the maximum expected current that may be drawn by a particular

circuit at any given time. For single items of equipment it is set by assessment of the

connected load. In light and power circuits, or other circuits with more than one point

per final sub-circuit, the maximum demand of a final sub-circuit is set by limitation

(clause C2.5.1). The purpose of the final sub-circuit will determine the number of

points that may be connected to that final sub-circuit.

Exercise 2 highlighted that load in an installation is divided into a number of circuits

logically arranged into group loads of a similar type onto the same circuit. The more

load connected to a single circuit the higher the demand will be; light and power

circuits tend to have a large number of points connected to a single circuit. If too much

load is connected at the same time the circuit protection device will operate,

automatically disconnecting the circuit. Circuits for appliances such air conditioning,

hotplates and hot water systems are arranged so that each appliance is on its own

separate final sub-circuit for maintenance and testing purposes.

The key to circuit design is to limit the number of lights or socket outlets on a particular

circuit so the circuit protection device does not trip, while still using the minimum

number of circuits to keep installation cost to a minimum. Table C8 gives guidance to

the recommended number of points per final sub-circuit.

Daily Demand - different types of installations will use power in different ways. For

example socket outlets installed in a domestic installation may rarely ever be used, but

in a non domestic installation such as a factory, the socket outlet is probably installed

for a certain purpose and will most likely be in use frequently. For the circuit to function

correctly as intended the number of points per final sub-circuit will be less in the

factory or commercial office.

Seasonal Demand - the demand of circuits that supply appliances such as air

conditioner will very throughout the year. Most A/C units use more current to heat than

to cool. The higher current must be taken as the maximum demand.

Connected load - is the actual current drawn by the circuit with no “diversity” applied.

It can be found on the compliance plate of an appliance or calculated using the power

equation transposed to find current.


Page 11 of 181



Determining the current for load devices can be found using the following:

Single phase appliances Three phase appliances

where

I = Current in Amperes IL = Line current in Amperes

V = Voltage in Volts VL = Line voltage in Volts

λ = power factor λ = power factor

In circuits with only one point per circuit (designated circuit) this current becomes the

maximum demand of the circuit.

Exercise 4:

Determine the line current drawn by a 400 Volt, 13 kW three phase air-conditioner

operating at a rated power factor of 0.95.

V = ……..………. _____________________________________________________

P = ……………… _____________________________________________________

λ = ...……………. _____________________________________________________

I = ? _____________________________________________________

_____________________________________________________

Exercise 5:

Determine the current drawn by a 230 Volt, 6 kW electric cooktop (resistive load)

V = ……..………. _____________________________________________________

P = ……………… _____________________________________________________

λ = ...……………. _____________________________________________________

I = ? _____________________________________________________

_____________________________________________________

Note: Cook tops, stoves, ovens and hotplates in domestic installations are allowed

some diversity in the calculation of their maximum demand. AS/NZS 3000 Table C4

lists the maximum demand current values for domestic appliances.

Temperature controllers fitted to these appliances operate to cycle the elements on

and off. As a result, not all of the elements will be on or off at the same time therefore

the current drawn by the appliance will be less than the rating on the name plate.


Page 12 of 181



Exercise 6:

Refer to Appendix C – Circuit Arrangements

Read the following and complete the exercise below.

Clause 5.1

Clause 5.2

Table C8

footnotes to Table C8

A Domestic Home is wired using T.P.S. cable and has the following load items

installed:

36 lights (10A C.B.)

24 Double 10A Socket Outlets (20A C.B.)

1 25A Single Phase Air-conditioner (25A C.B.)

1 3.6 kW Hot Water System (16A C.B.)

Complete the following table:

Circuit number

Load Type Protection Device / Rating

(A) Number of points per

circuit

1

2

3

4

5

6

7


Page 13 of 181



Exercise 7:

Refer to figure 4 below of a domestic home and determine how the circuits will be

separated.

Note:

For light and power

circuits, list the

number of points

you have grouped

together on each

circuit.

Circuits:

Total number of final Subcircuits:_________ (answers may vary depending on design)

_____________ _____________ _____________ _____________

_____________ _____________ _____________ _____________

_____________ _____________ _____________ _____________

Appliance

Specifications:

Oven: 3.8 kW

HWS: 4.8 kW O/Peak

Cooktop: GAS

Dishwasher:

10A plug in

Rainwater Tank:

10A plug in

Refrigerator:

10A plug in

RW

T


Page 14 of 181



Exercise 8:

A Commercial Office is wired using T.P.S. cable and has the following load

items installed:

43 lights (20A C.B.)

23 10A Socket Outlets (20A C.B.)

Complete the following table:

Circuit number

Load Type Protection Device / Rating

(A) Number of points per

circuit

1

2

3

4

5

6

7


Page 15 of 181



CIRCUIT SCHEDULES

Circuit schedules are used to detail which protection device controls which circuit.

Domestic homes usually do not require schedules due to the small number of circuits

installed and simply label the switchboard or distribution directly.

In industrial or commercial installations, the number of circuits is increased and

schedules are required.

An example is shown in figure 5.

Installation By: Sparky

Phone: 0414 123 456

Sub Board No.: DB1-G1

Fed From: Main Switchboard C.B.10

Cable Size: 25mm 4core XLPE + E

Pos. Amps Designation Pos. Amps Designation

1 32 3 Phase induction Motor – workshop 1 2 20 Power cct 1 – General GPO’s front office

3 32 3 Phase induction Motor – workshop 1 4 20 Power cct 2 – General GPO’s front office

5 32 3 Phase induction Motor – workshop 1 6 20 Power cct 3 – General GPO’s workshop 1

7 32 3 Phase wall outlet – workshop 1 8 20 Kitchen – Dishwasher GPO

9 32 3 Phase wall outlet – workshop 1 10 20 Kitchen – Steam Oven GPO

11 32 3 Phase wall outlet – workshop 1 12 20 Kitchen – Microwave GPO

13 25 10 HP Daikin Air Conditioning Unit No. 01 14 20 Kitchen – Bench GPO’s

15 25 10 HP Daikin Air Conditioning Unit No. 01 16 20 Power cct 4 – General GPO’s warehouse

17 25 10 HP Daikin Air Conditioning Unit No. 01 18 20 Power cct 2 – General GPO’s workshop 2

19 25 10 HP Daikin Air Conditioning Unit No. 02 20 20 Power cct 1 – General GPO’s bathroom

21 25 10 HP Daikin Air Conditioning Unit No. 02 22 20 Lighting cct 1 –front office

23 25 10 HP Daikin Air Conditioning Unit No. 02 24 10 Lighting cct 2 - kitchen

25 20 3 phase Welder – workshop 2 26 10 Lighting cct 3 –bathroom

27 20 3 phase Welder – workshop 2 28 20 Lighting cct 4 - warehouse

29 20 3 phase Welder – workshop 2 30 20 Lighting cct 5 – workshop 1

31 Spare 32 20 Lighting cct 6 – workshop 2

33 Spare 34 20 Lighting exterior security

35 Spare 36 20 Security panel – GPO

37 Spare 38 Spare

39 Spare 40 Spare

41 42

Figure 5 .


Page 16 of 181



ARRANGEMENTS FOR SELV AND PELV CIRCUITS

Refer to Clause 1.5.7 – Basic and fault protection by use of extra-low voltage:

Complete the following:

S= ____________________

E= ____________________

L= ____________________

V= ____________________

P= ____________________

E= ____________________

L= ____________________

V= ____________________

Figure 5

Protection by SELV is used in high risk situations where the operation of electrical

equipment presents a serious hazard to safety. One typical location is Zone 0 in a

pool zone which is in the water container itself ie: pool lighting where the nominal

voltage must not rise above 12V ac or 30V ripple free dc. In this system there is NO

return path for current via earth as protective conductors are NOT permitted to be

installed.

Protection by PELV is used where extra low voltage is required, but the risk of

electric shock is much lower than what would be expected for a SELV wiring

situation. As with a SELV supply, a safety isolation transformer is commonly

employed to provide electrical separation from the low voltage wiring system on the

primary side, with the addition of circuit protection in the active conductors of the ELV

circuit. Although a protective earth is not required on the secondary of a PELV

transformer, one can be used should the connected equipment need it. See figure 5.

Set out below are some requirements that must be met for SELV and PELV systems.

Figure 5 shows 2 circuit arrangements that provide ‘extra low voltage’ as a method of

safety and protection.


Page 17 of 181



Refer to Clause 1.5.7

Separated extra-low voltage (SELV) or protected extra-low voltage (PELV) systems

may be used to provide both basic and fault protection subject to the following:

a) The nominal voltage shall not be capable of exceeding the limits for _______________ __________ (50 V a.c. or 120 V ripple-free d.c.) and the source of supplyis arranged so that it cannot exceed these values.

b) Circuits shall be electrically ___________ from each other and from circuits at___________ voltages.

c) Live parts of SELV circuits shall not be connected to __________ or to protectiveearthing conductors that are part of other circuits or to other live parts.

d) Live parts of PELV circuits shall be protected from direct contact by ___________

or ______________ unless the voltage does not exceed 25 V a.c. or 60 V ripple-

free d.c. in dry areas where a large contact area with the human body is not

expected or 6 V a.c. or 15 V ripple-free d.c. in all other areas.

Clause 7.5.4 also sets out that live parts of SELV and PELV circuits shall be

electrically separated from each other and from other higher voltage circuits, however,

it makes the following exception:

SELV and PELV circuit conductors installed in accordance with Clause 3.9.8.3 may be

contained within the same wiring system as low voltage circuits.

In general, to apply the exception, the ELV cable needs to double insulated OR

insulated to the same level of the LV cable which it is enclosed with.

Refer to Clause 7.5 – Extra-low Voltage Electrical Installations

Extra-low voltage electrical installations shall be one of the following systems—

SELV

PELV

NOTE: Clause 7.5 of AS/NZS3000:2007, replaces or modifies requirements of other

Sections in the Standard.

Any electrical installation operating at extra-low voltage but does not comply with the

SELV or PELV requirements of Clause 7.5, it shall be deemed to be operating at low

voltage and subject to the relevant requirements.


Page 18 of 181



Refer to Section 7: clause ___________ Sources of supply by SELV and PELV

The source supplying an SELV or a PELV system shall be one of the following:

(a) A __________________________________ complying with AS/NZS 61558.

(b) A source of current independent of a higher voltage supply, such as an

engine-driven __________, or an electrochemical source, such as a ________.

(c) A source of current separated from higher voltage electrical installations, such as

a motor-generator set, with electrically separate windings having a degree of

electrical separation equivalent to that required by Item (a).

(d) Certain electronic devices complying with appropriate Standards.

Refer to Section 7: clause ____________ Arrangement of SELV circuits

Live parts of SELV circuits shall not be connected to earth or protective earthing

conductors that are part of other circuits or to other live parts.

Class III equipment (clause 1.4.29) may only be connected to and supplied by a SELV

system that will not supply circuit equipment any higher than ELV (max. 50V ac or

120V ripple free dc)

SELV circuits shall not be connected to—

_________________________

_________________________

__________________________________________________________

__________________________________________________________

Where the nominal voltage exceeds 25 V a.c. or 60 V ripple-free d.c., protection

against electric shock in normal service (direct contact) shall be provided by—

(i) barriers or enclosures with a degree of protection of at least IPXXB or

IP2X; or

(ii) insulation capable of withstanding a test voltage of 500 V a.c. for 1 min.

Note: There are exceptions to this clause.

IPXXB – Designates no specific rating for solid objects or moisture, however the

letter B requires that a test finger should not be able to penetrate more than

80mm and must not come in contact with hazardous parts

IP2X – Designates that full penetration of a 12.5 mm diameter sphere is not allowed.

The jointed test finger shall have adequate clearance from hazardous parts

Further IP Ratings may be determined by referring to Appendix G.


Page 19 of 181



Refer to Section 7: clause ____________ Arrangement of PELV circuits

The following applies for PELV circuits, where one conductor of the output circuit is

earthed.

Basic protection shall be provided by—

(a) __________ or _____________ affording the degree of protection at least IPXXB

or IP2X

(b) insulation capable of withstanding a test voltage of 500 V a.c. for 1min.

Note: There are exceptions to this clause.

Further AS/NZS 3000 requirements need to be considered when installing SELV or

PELV circuits. If these requirements are not met, then the system must be treated as

and meet the requirements of a Low Voltage (LV) system.

Refer to the following clauses and complete exercise 9:

Clause 7.5.7 to 7.5.11

Exercise 9

Voltage drop at any point in an extra-low voltage electrical installation shall

not exceed ________% of the nominal value at IFL unless the equipment is

designed for such operation.

The supply to an extra-low voltage electrical installation shall be

controlled by a ________ ___________ or switches operating in all unearthed

conductors, unless it is fed from a LV supply where a main switch will

disconnect supply.

Every extra-low voltage circuit shall be individually protected at its origin

against overload and short-circuit currents by a protective device that

complies with clauses _______ and _______ .

List the 3 requirements that plug and socket-outlet devices, including

installation couplers, need to comply to when used for SELV and PELV

circuits:

a) ___________________________________________________________

b) ___________________________________________________________

c) ___________________________________________________________

Conductors and insulation of cables used for extra-low voltage

electrical installations shall be _____________ for the intended purpose.


Page 20 of 181


Version 1 UEENEEG063A S2 – Cct.&Control Arrangement .

ARRANGEMENTS FOR ISOLATED SUPPLY

Refer to Clause 7.4 – Electrical Separation (Isolated Supply)

Note: The expression ‘electrical separation’ has the same meaning as ‘isolated supply’.

As has been previously discussed, whenever current flows, whether it is normal load

current, overload current or fault current, it wants to return the source from which it

originated, in order to complete the circuit.

Isolated supply systems are used for electrical safety. As there is no connection

between the isolated circuit conductors of an isolated supply and earth, a person in

connection with the general mass of earth whilst in contact with live circuit conductors

will not receive a potentially lethal electric shock. That is, fault current cannot make its

way back to the transformer secondary winding through earth as there is no path.

Unlike a SELV or PELV wiring system, an isolated supply need not operate at ELV.

See the circuit arrangements below from AS/NZS 3000:2007 figure 7.7


Page 21 of 181


UEENEEG063A S2 – Cct.&Control Arrangement Version 1 Disclaimer: Printed copies of this document are regarded as uncontrolled.

Isolated supply systems are commonly used for wiring in medical rooms (hospitals),

electrical laboratories and in some instances for audio and visual equipment to reduce

and filter ‘noise’ in the electrical supply system.

Protection by electrical separation shall be compliant with Clauses 7.4.2 to 7.4.4, and

with—

(a) Clause 7.4.5 for a supply to ____________________________; or

(b) Clause 7.4.6 for a supply to _______________ item of equipment.

Refer to Clause 7.4.3 – Arrangement of circuits

Separated circuits shall comply with the following requirements:

(a) Circuit voltage shall not exceed _______ V.

(b) All live parts of a separated circuit shall be reliably and effectively electrically

____________ from all other circuits, including other separated circuits and earth.

(c) Exposed conductive parts of electrical equipment supplied by a separated circuit

shall not be connected to the protective earthing conductor, or the exposed

conductive parts, of the source of supply.

(d) Cables and supply flexible cords to electrical equipment shall be protected against

mechanical damage or otherwise arranged to ensure that any damage that might

occur is readily visible.

Refer to Clause 7.4.5 - Single item of electrical equipment

Where a separated circuit supplies a single item of electrical equipment, any exposed

conductive parts of the electrical equipment shall ________________________ to the

______________________ parts of any other circuit, including other separated circuits

or earth.

Refer to Clause 7.4.6 - Multiple items of electrical equipment

Where a separated circuit supplies more than one item of electrical equipment, the

following shall apply:

(a) Any exposed conductive parts of the separated circuit shall be connected

together by an insulated equipotential bonding conductor that is not connected to:

______________; or

a _______________________ conductor or exposed conductive

parts of

another circuit, including another separated circuit; or

any ______________________________________.


Page 22 of 181



(b) The designated earthing contact of any socket-outlet installed on the separated

circuit shall be connected to the ______________________conductor.

(c) The designated protective earthing conductor in any supply cable or flexible cord

to electrical equipment (other than Class II [double or reinforced insulation]

equipment) connected to the separated circuit shall be connected to the

_______________________conductor.

(d) Exposed conductive parts of the ____________________ that are earthed, shall

not be simultaneously accessible with any _________________________ of the

separated circuit.

(e) A protective device shall operate to disconnect the separated circuit ___________

in the event of two faults resulting in exposed conductive parts being connected to

live parts of different polarity..

In addition to the mandatory testing requirements of Section 8 of AS/NZS3000, the

separation of each separated circuit (transformer secondary winding or isolated

winding generator output) and the wiring to the socket-outlet shall be individually

confirmed.

Additional tests to verify separation shall be verified by a measurement of the

insulation resistance between the separated circuit and:

if a transformer is the source of the separated supply, the transformerprimary winding; and

any other wiring; and

any other separated circuit; and

earth

In each instance, the Insulation resistance values obtained shall be not less than

1 MΩ, when tested at a voltage of 500 V d.c.

CONTROL OF ELECTRICAL INSTALLATIONS AND CIRCUITS

The term ‘control’ as applied to electrical installations can be defined in a number of

ways. There are control requirements for:

_____________________________________

_____________________________________

_____________________________________

In addition, the method of control for many parts of an electrical installation often

provides an effective means of isolation.


Page 23 of 181



Control of an entire installation or part thereof, may be required for a number of

reasons. These include:

____Isolation of the installation_____

____emergency reasons__(fire, machine safety,etc)__

____maintenence__________

___functional control___(machines, appliances)___

Control and isolation of installations and circuits is commonly provided by the

installation of the following devices:

_________________________

_________________________

_________________________

Figure 7 Figure 8 Figure 9 Figure 10

Figure 7: Din rail mounted Circuit Breaker (Protection and Isolation)

Figure 8: Din rail mounted Switch (Isolation only)

Figure 9: Various Isolating Switches (Isolation only)

Figure 10: Push Button (Circuit control: emergency stop – No protection or Isolation)

NOTE: For the purpose of this section, ‘control of electrical installations and circuits’

will focus on control and isolation of mains, sub-mains and final sub-circuits only, not

circuit control as provided for by start/stop stations, relays, contactors and emergency

stop buttons and the like. This type of circuit control will be covered in later units of

study.


Page 24 of 181



Which section of AS/NZS3000 sets out the requirements for general arrangement,

control and protection of electrical installations?

___________________________

When selected devices for control of installations and circuits, consideration needs to

be given to suitability of the device, including:

_____(2.1.2)____________________

_________________________

_________________________

_________________________

________ip rating_________________

Refer to definitions: Clause 1.4.62 – Isolation (isolating function)

Isolation is a function intended to cut off the supply from:

___________________________ or,

___________________________ ,

by separating it from every source of electrical energy for reasons of safety.

Refer to definitions: Clause 1.5.2 – Control and Isolation

Electrical installations shall be provided with control and isolation devices to prevent or

remove:

________________________________________ and to allow

________________________________________.

This may incorporate a device that effectively isolates the equipment from all sources

of supply external to the equipment.

The control of safety services shall be arranged so that the control devices are:

_________________________________________ and are not

______________________________________________________

__.

An isolation device shall interrupt all:

_____________________ .


Page 25 of 181



NOTE: In some cases, an isolation switch may operate in the neutral conductor.

However, the neutral conductor shall NOT be operated independently of the

associated active conductors.


Page 26 of 181



An isolation device or switch shall not interrupt:

__________________________ or

______________________________________________________

___.

Briefly explain why it is important that an isolation device NOT open circuit a

protective earth or PEN conductor (combined protective earth / neutral):

__________________________________________________________________

__________________________________________________________________

Refer to Clause 2.1.2 – Selection and Installation

Switchgear and control gear shall be selected and installed to perform the following

functions:

(a) Provide ____________or ______________ of the electrical installation, circuits

or individual items of apparatus as required for maintenance, testing, fault

detection or repair.

(b) Enable ______________ disconnection of supply in the event of an overload,

short-circuit or excess earth leakage current in the _______________ part of

the electrical installation.

(c) Provide _____________ of the electrical installation against failure from

_____________ or _____________ conditions.

(d) Provide for switchgear and control gear to be ___________ and interconnected

on__________________, enclosed against external influences, and located in

accessible positions.

(e) _____________ control and protect the circuit arrangements without affecting the

reliability of supply to, or failure of, other parts of the installation.

Refer to Clause 2.3 – Control of Electrical Installation – General

Electrical installations shall be provided with devices to prevent or remove hazards

associated with the electrical installation and for maintenance of electrically activated

equipment.

Any device provided shall comply with the relevant requirements of Clause 2.3, and for specific purposes, shall comply with the following clauses:

(a) Isolation: Clause ______________

(b) Emergency: Clause ______________

(c) Maintenance: Clause ______________


Page 27 of 181



(d) Functional Control: Clause ______________


Page 28 of 181



Refer to Clause 2.3.2 – Common Requirements

Every circuit shall be capable of being isolated from each of the supply conductors,

in accordance with Clause ___________ or ____________.

Provided that the service conditions allow and the appropriate safety measures are

maintained, a ___________________ may be isolated by a ____________ switch.

Provision shall be made to enable isolation of electrical equipment and to

prevent electrical equipment from being _________________energized.

Exercise 10:

List 3 precautions which may be used to prevent electrical equipment from being

inadvertently (accidently) energized.

(a) _______________________________________________________________

(b) _______________________________________________________________

(c) _______________________________________________________________

Refer to Clause 2.3.2.1.1 – Alternating Current Systems:

Read t the requirements of this clause and answer the following:

In a 3 phase circuit how many active conductors are required to be switched

by the isolation device?

_________________________________________________________________

May an isolation device be placed in the neutral of a consumer’s main or a

P.E.N. conductor?

_________________________________________________________________

Are there any exceptions that would allow the neutral of a consumer’s main

neutral or a P.E.N. conductor to be switched or isolated?

_________________________________________________________________

May an isolation device be placed in a circuit other than in a consumer’s main

neutral or a P.E.N. conductor?

_________________________________________________________________

As discussed earlier, is permitted to switch an earthing conductor or PEN?

_________________________________________________________________


Page 29 of 181



Refer to Clause 2.3.2.1.2 – Direct Current Systems:

Common DC systems include the output of Photo-Voltaic (PV) systems, Extra Low

Voltage systems, battery backup systems, some machine control circuits and the like.

Read the requirements of this clause and answer the following:

In a d.c. circuit how many conductors are required to be switched by the isolation

device?

________________________________________________________________

how many conductors are required to be switched by the isolation device if it is installed

in an Extra Low Voltage (ELV) or a circuit where one pole is connected to earth?

________________________________________________________________

Refer to Clause 2.3.2.2.1 – Devices for Isolation

Devices for isolation shall effectively isolate all active supply conductors from the

circuit.

A semiconductor (solid-state) device shall not be used for isolation purposes.

A solid-state device is __________________________________________________

____________________________________________________________________

Read the Requirements of this clause and answer the following:

What do the symbols “O” and “I” indicate?

_________________________________________________________________

Should an isolation device be readily available / accessible?

_________________________________________________________________

What current should the isolation device be able to safely interrupt?

_________________________________________________________________

Clause 2.3.2.2.2

All devices used for isolation shall be clearly identified to indicate the circuit or

equipment that they isolate.


Page 30 of 181



Refer to Clause 2.3.3 – Main Switches

The purpose of Main (isolation) switches is to provide a means of disconnection of the

electrical supply to the installation in the case of an emergency. Main switches need to

be readily locatable and accessible by emergency services personnel, including;

Fire services

State Emergency Services (SES)

Local Supply Authorities

Electricians and qualified service personnel are also required to use Main switches to

isolate supply for the purpose of maintenance or repair.

Main switches are also required to be arranged so that supply can be cut to “general”

parts of the installation while maintaining supply to safety services (Clause 7.2) such as;

Fire and smoke control equipment

Evacuation equipment

Lifts

Refer to Clause 2.3.3.1 – General (Main Switches)

The supply to every electrical installation shall be controlled on the main switchboard by

a main switch or switches that control the whole of the electrical installation.

Where multiple supplies are provided, each supply shall be controlled by a main switch

or switches on the main switchboard for each supply.

How should Main switches be identified?

_________________________________________________________________

What are the requirements for Main switches supplying safety services?

_________________________________________________________________

Refer to Clause 2.3.3.2 – Number of Main Switches

What is the maximum number of main switches permitted in a domestic installation?

_________________________________________________________________

How many main switches would be required if a domestic installation had off-peak?

_________________________________________________________________

A block of 3 units has 3 meters, 1 per unit, and a 4th meter for common lighting. How

many main switches will be on the Main Switchboard?

_________________________________________________________________


Page 31 of 181



Refer to Clause 2.3.3.3 – Location

In general, main switches shall be:

_____________________________ , and located;

_______________________________________.

In multiple installations such as living units, flats etc, each occupier shall have:

_______________________________________________________

Refer to Clause 2.3.3.4 – Identification

Main switches shall be:

Identified as

__________________________________________________

Be readily

____________________________________________________

Marked to indicate

_____________________________________________

If the operation of a main switch brings in to function an alternate supply,

the alternate supply main switch location shall be

________________________

Where supply is provided at more than one point in any building, a prominent

notice shall be provided at each main switchboard, indicating the presence of

other supplies and the location of other main switchboards.

* An example of this would be an alternate supply fed to a main switchboard

from a PV solar grid connected system

Figure 11

Refer to Clause 2.3.4.3 – Alternative supply

Circuits 1 - 11


Page 32 of 181



Where an electrical installation, or part thereof, is provided with an alternative supply in

accordance with Clause 7.3, an isolating switch shall be provided at the source of

supply or at a switchboard, in accordance with Clause 7.3.

Sample labelling for general and alternate supplies are shown in figure 11.

Further requirements are set out by AS/NZS3000 for the control and isolation of

electrical installations and circuits which will be covered in further units of study.

Reference to such requirements is set out below in clause 2.3.4.5.

Refer to Clause 2.3.4.5 – Appliances and accessories

Appliances and accessories, including motors, shall be provided with devices for

isolation and switching, in accordance with relevant clauses of Sections 4 and 7.

These clauses include the following:

Socket-outlets .………………………………….…..………………...… Clause 4.4

Cooking appliances………………………………..……………….. …. Clause 4.7

Water heaters…………………………………………………………… Clause 4.8

Room heaters …………………………………...……………………… Clause 4.9

Heating cables for floors and ceilings …………................................ Clause 4.10

Electricity converters …………………………………………………... Clause 4.12

Motors …………………………………………...…………………......... Clause 4.13

Capacitors …………………………………………............................... Clause 4.15

Safety services …………………………………………………….......... Clause 7.2

Electricity generation systems ……………...…………………………. Clause 7.3

SAFETY SERVICES

When fire or some other emergency occurs in a building emergency services must

respond quickly and efficiently to prevent loss of life and/or injury. Main switches of

buildings requiring safety services must arranged and identified to aid emergency

services personnel to isolate only the general supply and leave safety services

energised.

Refer to Clause 7.2 – Safety Services

The requirements of clause 7.2.1.1 – General, are to ensure that:

_________________________________________ from electrical

equipment that is required to operate;

_________________________________________ for which there is no

alternate supply.


Page 33 of 181




Page 34 of 181



Set out below is a summation of the safety services sub-clauses set out by clause 7.2.

Safety services may be referred to as ‘emergency systems’ in some installations

The Building Code of Australia (BCA) refers to safety services as ‘emergency

equipment’

In general , each part of an electrical installation supplying a safety service shall

be controlled by a main switch that is separate from main switches used to

control:

- parts of a general installation

- other safety services

There shall be no limit to the number of main switches installed for the

control of safety services.

Main switches for safety services shall be connected on the supply side of all

general electrical installation main

Each individual safety service shall have a separate main switch NOTE:

All main switches shall be clearly identified to indicate the safety service that

they control.

All main switches shall be marked ‘IN THE EVENT OF FIRE, DO NOT SWITCH

OFF

All main switches shall be identified by contrasting colouring

Where an alternative supply is provided, a changeover switch shall be

installed on the main switchboard to allow supply from the alternative system

to be connected to the safety services.

Exercise 11:

Read clauses 7.2.1.2 and 7.2.1.3 and list 6 types of safety service that would be

separate from one and other and controlled by their own main switch:

_______________________________

_______________________________

_______________________________

_______________________________

_______________________________

_______________________________


Page 35 of 181



ISOLATION SWITCHES FOR MECHANICAL MAINTENANCE

Some items require isolation for maintenance, repair or testing purposes. In these

cases the load is isolated separately to reduce loss of supply and inconvenience.

A means of disconnecting electricity supply or shutting down needs to be provided

where mechanical maintenance might involve a risk of physical injury.

Exercise 12:

Read clause 2.3.6.1 and answer the following:

List 2 types of injury that may occur if equipment is not shut down and isolated:

________________________________

________________________________

List 6 Examples of electrical installations where means of shutting down for mechanical

maintenance are used:

________________________________

________________________________

________________________________

________________________________

________________________________

________________________________

Refer to Clause 2.3.6.2 – Devices for Shutting Down

Devices for shutting down for mechanical maintenance shall:

(a) require _____________ operation; and

(b) clearly and reliably indicate the ‘______’ position; and

(c) be ___________ or ___________ so as to prevent _______________________.

Refer to Clause 2.3.6.3 - Installation

Devices for shutting down for mechanical maintenance shall be inserted in the main circuit.

Where switches are provided for this purpose they shall be capable of interrupting the

___________________ of the relevant part of the electrical installation.

Refer to Clause 2.3.6.4 - Identification

Devices for shutting down for mechanical maintenance shall be placed and marked so

as to be _____________________ and ______________ for their intended use.


Page 36 of 181



Refer to Clause 4.13.1.1 – Switching Devices (for motors)

Isolation switches in motor circuits are installed to provide protection against injury

from mechanical movement.

Every motor shall be provided with a switching device capable of:

(a) starting and stopping the motor; and

(b) emergency stopping, in accordance with Clause 2.3.5; and

(c) _______________________________________________________________

An isolating switch is only required for motors rated above ______________.

Refer to Clause 4.13.1.2 – Rating of Switches (for motors)

Isolating switches for motors shall have a rating of not less than:

(a) the _________________ of the motor when installed directly in the motor supply

circuit; or

(b) the ____________________________ when installed in the motor-starter circuit.

NOTE: Any switch operating directly in the motor-supply circuit shall be capable of

safely interrupting the locked-rotor or stall current of the motor.

AS/NZS 3000 default values used to determine locked rotor current are:

________________ the full load current for A.C. motors

________________ the full load current for D.C. motors

Correctly rated switches marked with the letter ‘_____’ are suitable for interrupting

locked rotor current.

FUNCTIONAL CONTROL SWITCHES

Functional switching is required for _________________ only and not for safety

reasons. Functional switches do not necessarily provide isolation of electrical

equipment, but merely a way to control or operate it.

Functional switching devices may be:

Switches

Semiconductor devices

Contactors


Page 37 of 181



Functional switching devices:

Shall be suitable for the intended purpose and location

Shall be suitably rated for the loading

Shall be robust enough to suit the frequency of operation

In some circumstances, need not switch or interrupt all live conductors

May require a de-rating factor applied if controlling low power factor loads

(motors, fluorescent lighting etc.)

Unless specific provision is required, a functional switching device need not be

identified to indicate the ‘ON’ or ‘OFF’ position (eg: light switches).

Refer to Clause 4.7.1 –Switching device (Cooking Appliances)

A circuit for a fixed or stationary cooking appliance having an open cooking surface

incorporating electric heating elements, such as

Cooktops

deep fat fryer

barbecue griddle etc;

shall be provided with a switch, operating in _______ active conductors, mounted near

the appliance in a visible and _______________________ position.

NOTE: An exception to this clause exists for cooktops etc. in public parks

A functional switch for a cooktop should be mounted within _____ metres of the

appliance.

Does a built in wall oven require a functional switch? ___________________.

Does an upright stove require a functional switch? _____________________.

What recommendation is given for functional switches installed to control

domestic appliances? ___________________________________________.


Page 38 of 181



CONTROL ARRANGEMENTS FOR COMPLETE INSTALLATIONS

Below sets out some typical examples of main switch and control arrangements for

some varying installations.

Figure 12 – Single phase, single tariff

Figure 13 – Single phase,

single tariff with sub-mains


Page 39 of 181



Service Protective Device

MTariff Meter

MAIN SWITCHGeneral

C.B.Lights

C.B.Power

C.B.Range

Consumer’s Mains

MAIN SWITCHLifts

IN THE EVENT OF FIRE,

DO NOT SWITCH OFF

C.B.Lift 1

C.B.Evacuationequipment

C.B.Lift 2

MAIN SWITCHEvacuationEquipment

IN THE EVENT OF FIRE,DO NOT SWITCH OFF

Figure 14

Single phase,

dual tariff.

Figure 15 shows the relationship between general equipment, emergency services

and the corresponding main switches.

Figure 15


Page 40 of 181



Figure 16 below is an extract from AS/NZS3000:2007 (figure 7.2) showing an example

of connection of an alternate supply to a switchboard.

Figure 16

***************NOTES***************

NAME: Practical 2

Page 41 of 181





– REMEMBER –



Practical 1 - Basic Relay Circuits

Page 42 of 181



.

Section 3

Page 1 of 181


UEENEEG063A Section 3 – Prot. Indirect Contact Version 1 Disclaimer: Printed copies of this document are regarded as uncontrolled.


In the following statements one of the suggested answers is best. Place the identifying

letter on your answer sheet.

1. Which of the following considerations is not necessary in determining the number

and type of circuits within an electrical installation?

Load on the various circuits.

Location of the points or load.

Exposure to external influences.

Seasonal and daily variations of demand

When selecting a circuit breaker for a water heater final sub-circuit, its current rating

should be:

equal to or less than the demand of the final sub-circuit and equal to or less than the cable rating

equal to or greater than the demand of the final sub-circuit and equal to or less than the cable rating

equal to or less than the demand of the final sub-circuit and equal to or greater than the cable rating

equal to or greater than the demand of the final sub-circuit and equal to or greater than the cable rating.

A separate final sub-circuit is recommended for any single point of load exceeding;

16A.

20A.

25A.

32A.

The recommended number of lighting points that can be connected to a circuit wired in

1.0 mm2 TPS cable and protected by a 6A type C circuit breaker in a domestic

installation is:

10

12

20

unlimited

S3 – Prot. Against Indirect Contact

Page 2 of 181


Version 1 UEENEEG063A Section 3 – Prot. Indirect Contact

The recommended number of double 10A socket outlets that can be connected to a

circuit wired in 2.5 mm2 TPS cable and protected by a 20A type C circuit breaker in

a factory without air conditioning is:

5

10

20

Unlimited

The switch used to isolate a 12.5 kW range (cook top and oven) that is connected to

two phases and neutral, would have as a minimum:

one pole.

two poles.

three poles.

four poles.

For a single domestic installation, with a maximum demand of less than 100 A, the

maximum number of main switches per tariff is

1

6

10

no limit.

A main switch should be located;

as close as possible to the load it isolates.

at the main switch board.

at the distribution board.

point of supply.

The maximum permissible height for a main switch for a main switch above the

ground, a floor or platform is;

0.6m

1.2m

2.0m

2.5m


Page 3 of 181



It is not permitted to install an isolation switch in;

Active conductors

Neutral conductors

Protective Earthing conductors

Switch wires

A house contains :

22 x lighting points protected by a 10 A C.B

16 x double 10 A S/O’s protected by a 20 A C.B.

1 x 15 A S/O for a clothes drier protected by a 20 C.B.

1 x 13 A A/C unit protected by a 20 C.B

1 x 800 W heat pump HWS. protected by a 20 C.B

Determine the number of circuits and the number of point per final sub-circuit required.

Circuit

number

Purpose / load Protection

Device /

Rating

(A)

Number of

points per

circuit

1

2

3

4

5

6

7


Page 4 of 181



For the house in tutorial question 11 complete a circuit schedule;

Pos. Amps Designation Pos. Amps Designation

1 2

3 4

5 6

7 8

9 10

11 12

13 14

15 16

17 18

AS/NZS 3000 defines a SELV wiring system as:

_________________________________________________________________

_________________________________________________________________

_________________________________ AS/NZS 3000 reference ____________

AS/NZS 3000 defines a PELV wiring system as:

_________________________________________________________________

_________________________________________________________________

_________________________________ AS/NZS 3000 reference ____________

The nominal voltage of a SELV or PELV wiring system shall not be capable of

exceeding:

_________________________________________________________________

_________________________________ AS/NZS 3000 reference ____________


Page 5 of 181



Can an Extra Low Voltage cable be run in a common conduit with a cable supplied at

Low Voltage?

_________________________________________________________________

_________________________________ AS/NZS 3000 reference ____________

Can an AUTO-TRANSFORMER be used to step down the voltage to supply a SELV

or PELV wiring system? Explain your answer.

_________________________________________________________________

_________________________________________________________________

_________________________________ AS/NZS 3000 reference ____________

Unless acceptable by connected ELV equipment, the maximum permissible volt-drop

permitted in a ELV wiring system is:

_________________________________ AS/NZS 3000 reference ____________

List 4 items that SELV circuits shall NOT be connected to:

_________________________________________________________________

_________________________________________________________________

_________________________________________________________________

_________________________________ AS/NZS 3000 reference ____________

Explain why it is not permitted to connect a protective earthing conductor from a SELV

or PELV circuit to the primary of a supply system or any other circuit:

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________


Page 6 of 181



A circuit connected to an ISOLATED supply shall not exceed how many volts?

_________________________________ AS/NZS 3000 reference ____________

Can the equipotential bonding conductors connected between socket outlets of an

ISOLATED circuit be connected to the equipotential bond of the MEN system?

_________________________________ AS/NZS 3000 reference ____________

List the minimum values of Insulation Resistance that should be expected during the

following tests on a circuit connected to an ISOLATED supply:

Between transformer primary and secondary

windings:______________

Between Isolated circuit active conductors and

earth:________________

Between Isolated circuit equipotential boning conductors and

transformer primary earth

conductors:_____________________________________

AS/NZS 3000 reference _____________

List the resistance you would expect to measure between the equipotentially bonded

earth pins of multiple socket outlets connected as an ISOLATED circuit:

_________________________________________________________________


An electrical installation has an electric cook top. What are the requirements for the

functional switch and in what position must the switch be located?

_________________________________________________________________


Can the main switch for a pump that operates the fire sprinkler system in a building, be

installed downstream of the general services main switch?

_________________________________________________________________



Page 7 of 181



PROTECTION AGAINST

INDIRECT CONTACT

PURPOSE:

In this topic you will analyse the different methods and the requirements for

each used to provide protection against indirect contact with conductive

electrical components.



discuss how indirect contact with live parts of an electrical installation may

occur.

determine methods and devices that comply with the Wiring Rules for

providing protection against indirect contact.

list components of the 'automatic disconnection of supply' method of

protection against indirect contact.

define the terms ‘touch voltage’ and ‘touch current’.

draw / describe the current path when a short circuit fault to exposed

conductive parts of an appliance occurs.

determine the requirements for protection against indirect contact by the use

of Class II equipment and by electrical separation.

determine the requirements for additional protection by use of Residual

Current Devices (RCDs)

determine the requirements for protection against indirect contact by use of

extra-low voltage and electrical separation.

determine the requirements for protection requirements for damp situations.

REFERENCES:

1. Electrical Wiring Practice. 6th Edition. Petherbridge K & Neeson I, Volume 1

2. Electrotechnology Practice. 1st Edition. Hampson J

3. AS/NZS3000:2007


Page 8 of 181



7. INTRODUCTION

In section 1 of this unit, it was established that AS/NZS 3000:2007 clause 1.5.1, set out

the fundamental principles required to provide protection for the safety of persons,

livestock, and property against dangers and damage that may arise in the reasonable

use of electrical installations.

The three major risks for which the principles were designed to protect against were;

4. Shock current

5. Excessive temperatures

6. Explosion

In this section, we will focus on protection against shock current that may occur as a

result of indirect contact with conductive electrical parts.

7. FAULT PROTECTION (AGAINST INDIRECT CONTACT)

Refer to clause 1.4.35 - Contact, indirect:

Indirect contact is contact with a conductive part which is -

______________________________________________________________________________

______________________________________________________________________________

Exercise 1:

List 2 fault conditions that may cause conductive

parts of electrical equipment to become ‘live’ as a

result of the fault.

8. ________________________________________

9. ________________________________________

List 4 electrical items that may cause electric

shock as a result of indirect contact.

10. ______________________________________

__

11. ________________________________________

12. ________________________________________

13. ________________________________________

Refer to clause 1.4.78 – Protection, fault:

‘Fault Protection’ must be provided to protect against –

____________________________________________________________________

Figure 1


Page 9 of 181



When a person experiences an electric shock they are first exposed to a:

14. ‘Touch voltage’, that results in a

15. ‘Touch current’. See figure 2.

Figure 2

Refer to clause 1.4.2 - Accessible, readily:

The term accessible means –

___________________________________________________________________________

___________________________________________________________________________

Refer to clause 1.4.95 - Touch voltage:

A touch voltage is a voltage –

___________________________________________________________________

Refer to clause 1.4.94 - Touch current:

A touch current is a current –

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

Earth bar

Neutral link

MEN link

N

Main earth

A

A N

Appliance

Fault

Protective earth disconnected

Switchboard

Touch voltage

230V

kWh


Page 10 of 181



Clause 1.5.5 of the wiring rules sets out the requirements for fault protection.

Refer to clause 1.5.5.2 – Methods of protection

Protection against indirect contact may be provided by one or any combination of the

following methods –

16. ____________________________________________________________

17. ____________________________________________________________

18. ____________________________________________________________

19. ____________________________________________________________

20. PROTECTION BY AUTOMATIC DISCONNECTION

The automatic disconnection of supply method is the most common method for

protection against electric shock. Automatic disconnection is typically provided by one

or more of the following components installed in series with the circuit conductors:

21. Circuit breakers

22. Fuses (HRC)

23. Circuit breaker / RCD combination unit

24. Separate Residual Current Device (RCD)

Note: Separate RCD’s can only be used as ‘supplement’ protection in addition

to either circuit breakers or fuses.

25. A system of earthing to provide sufficient current for the protective

device to operate as required

Refer to clause 1.5.5.3 (a) – Protection by automatic disconnection of supply

The principle of protection via automatic disconnection of the supply is based on

preventing a person from being subjected to the touch voltage for a time sufficient to

cause organic damage by the touch current, in the event of an insulation fault.

In the event of such a fault the circuit protective device must interrupt the resulting fault

current sufficiently quickly to prevent the touch voltage persisting long enough to be

dangerous.

This method of protection is achieved by –

26. ______________________________________________________________________

27. ______________________________________________________________________


Page 11 of 181



Refer to clause 1.5.5.3 (b) – Touch voltage limits

In the event of a fault between a live part and an exposed conductive part that could

give rise to a prospective touch voltage exceeding –

28. _____________________________________________

or

29. _____________________________________________,

a protective device shall automatically disconnect the supply to the circuit of the

electrical equipment concerned.

Refer to clause 1.5.5.3 (d) – Disconnection times

The maximum disconnection time for 230/400V supply voltage shall not exceed the

following –

30. ________ seconds for final sub-circuits that supply –

a) socket outlets having rated currents not exceeding 63A

b) hand held class I equipment

c) Portable equipment intended for manual movement during use

31. ________ seconds for other circuits including sub-mains and final sub-circuits

supplying fixed or stationary equipment.

Automatic disconnection of the supply relies on a combination of two conditions -

32. the provision of a conducting path, known as the “______________________”,

to provide for circulation of the fault current; and

33. the interruption of the fault current within the maximum time by an appropriate

protection device.

Specific requirements for Earth Fault-loop impedance, including calculations of loop

impedances for varying installations and circuits will be covered in other topics of this

unit workbook.

A basic overview only is provided on the following page.


Page 12 of 181



Figure 3 illustrates the concept of the earth fault-loop. An appliance supplied via a final

sub-circuit has an earth fault in which the active conductor has come in contact with

the earthed frame of the appliance.

Figure 3

The earth fault-loop illustrated in figure 3 is represented by the ‘equivalent circuit’ diagram

of figure 4.

Figure 4

Fault

ZTX

Transformer ZDA ZCMA ZFSA

ZDN ZFSPE ZCMN

Point of supply

Appliance Main earth

N/L E/B

Fault

kWH

Customer installation

Distribution transformer secondary

Distribution lines

A

B

C

N

MEN link

Point of supply


Page 13 of 181



In the example shown in figures 3 and 4 – 34. if the touch voltage on the appliance frame rises to a value above ______V a.c.

the circuit breaker protecting the circuit must operate within the prescribed time

to isolate the faulty circuit.

35. Under fault conditions, the level of current that flows is only limited by the

____________________.

36. To ensure very fast operation of the circuit breaker the current that flows in the

earth fault-loop must be _________________.

37. Therefore the earth fault-loop impedance must be _______________________

to ensure operation of the protective device.

14. PROTECTION BY CLASS II EQUIPMENT

The installation of Class II equipment is another method of protection used to prevent

electric shock. Clause 1.5.5.4 details these requirements.

Approved class II equipment when manufactured does not require a protective earth

conductor.

In most cases however, a protective earth conductor will be required to be installed at

the point where the class II equipment is connected; for example, at a socket outlet

where a double insulated electric drill may be used.

As discussed in section 1, Class II equipment is defined in clause 1.4.28 as:

Class II - equipment where shock protection is afforded by the provision

of double insulation or reinforced insulation between live parts

and accessible conductive parts, and having no provision for

protective earthing of those conductive parts. This class of

equipment shall be marked with the symbol for Class II.

Table 1

Equipment Class

Protective Measures

Symbol

I Basic insulation + protective earth

II Basic insulation + supplementary insulation or reinforced insulation

III Separated extra-low voltage (SELV)


Page 14 of 181



Double insulation is defined as:

A system that comprises of ‘basic’ insulation and ‘supplementary’ insulation.

Twin and earth cable is double insulated. This is referred to as a double insulated

system, not to be confused with double insulated Class II equipment. In most cases,

single insulated Class I equipment will connect to a double insulated wiring system.

Double insulated hand-held electric equipment carries the ‘square in square’ symbol

as detailed in table 1.

Reinforced insulation is defined as:

Single insulation that provides a degree of protection against electric shock equivalent

to that of double insulation.

In general, double insulated and reinforced insulation means that failure of two

independent sections of insulation must occur before exposed conductive parts can

become ‘live’ in the event of a fault.

15. PROTECTION BY ELECTRICAL SEPARATION

The general requirements for protection by separation (isolated supply) have been

covered in section 2 of this workbook. Below is a review only of the requirements

covered in section 2 for electrical separation.

Electrical separation can provide protection from the potential hazard that may arise

from the rest of the installation. Electrically separating a portion of a system means to

electrically isolate it from the main supply grid and MEN system.

This method of protection typically uses a supply from:

38. __________________________________________

39. __________________________________________

40. __________________________________________

Figure 5 – A separated (isolated) supply for multiple socket outlets.


Page 15 of 181



Refer to clause 1.5.5.5 – Protection by electrical separation

Protection by electrical separation is intended, in an individual circuit, to prevent shock

current through contact with exposed conductive parts that might be energized by a

fault in the basic insulation of that circuit.

Live parts of a separated circuit shall:

41. ____________________________________________________________

Any protective bonding conductor associated with a separated circuit shall:

42. _____________________________________________________________

NOTE: Clause 7.4 contains requirements for protection by electrical separation.

16. PROTECTION BY EXTRA LOW VOLTAGE

As discussed in section 2 of this workbook, the use of Extra Low Voltage (ELV) is a

method for providing protection against electric shock. Below is a review only of the

requirements covered in section 2 for ELV systems.

By reducing the voltage to an extra low level, the hazards associated with electric

shock are greatly reduced.

Refer to Clause 1.4.98 –Voltage

Extra Low Voltage is defined as voltage:

43. _____________________________________________________

Protection can be provided by the use of:

44. ___________________________ or,

45. ___________________________

See figure 6.

Figure 6

Protection by SELV is used in high risk situations where the operation of electrical

equipment presents a serious hazard to safety. Typically, a SELV system is used to

supply a single piece of equipment such as a luminaire, where the output rating of the


Page 16 of 181



transformer is limited, and protection is provided by the protective device on the

primary side of the transformer. Some transformers also have fused secondary

windings.

It is requirement that in order for equipment to classified as Class III equipment, it must

be supplied by a SELV system.

Protection by PELV is used where extra low voltage is required, but the risk of electric

shock is much lower than what would be expected for a SELV wiring situation.

The main requirements for SELV and PELV systems are:

The nominal voltage shall not be capable of exceeding 50 V a.c. or 120 Vripple-free d.c.

Circuits shall be electrically segregated from each other and from circuitsat higher voltages.

Live parts of SELV circuits shall not be connected to earth or to protectiveearthing conductors that are part of other circuits or to other live parts.

Live parts of PELV circuits shall be protected from direct contact bybarriers or insulation unless the voltage does not exceed 25 V a.c. or 60 Vripple-free d.c. in dry areas where a large contact area with the humanbody is not expected or 6 V a.c. or 15 V ripple-free d.c. in all other areas.

Remember, Clause 7.5 provides specific deemed to comply requirements for the

arrangement of ELV circuits.

NOTE: Any electrical installation operating at extra-low voltage but does not comply

with the SELV or PELV requirements of Clause 7.5, shall be deemed to be operating

at low voltage and subject to the relevant requirements.


Page 17 of 181



46. ADDITIONAL PROTECTION BY RCDs

RCD operating principles will be covered in section 6 of this workbook. Set out below

are the basic fundamentals for additional protection by the use of RCDs.

Residual Current Devices (RCDs) may be used as a means of ‘supplement

protection’ for an electrical circuit. That is, they are installed in addition to other

protection devices such as circuit breakers or fuses.

The main applications of RCDs are -

47. personal protection;

48. fire protection; and

49. to reduce the risk of equipment damage in the event of a fault.

The use of fixed setting RCDs with a rated operating residual current not exceeding

______ mA, is recognized as providing additional protection in areas where excessive

earth leakage current could present a significant risk of electric shock.

RCDs do not provide protection against faults that occur between live conductors;

that is, no protection is provided for an electric shock that occurs as result of

phase to phase contact or contact between phase and neutral. RCDs operate in the

event of a fault to earth, where a person comes in contact with a live conductor and

earth.

The RCD operates by monitoring the current in all live conductors of the protected

circuit and any out of balance current due to an earth fault. The RCD amplifies any out

of balance condition and trips the circuit breaker when needed.

For protection of single-phase circuits, the active and neutral conductors pass through

a toroid as shown in figure 7.

Figure 7

Load

Trip

relay

L

N

RCD


Page 18 of 181



Load

Trip

relay

L

N

RCD

The current carrying conductors produce magnetic fields which will cancel each other if

there is no earth leakage. If there is no resultant magnetic field, the voltage produced

by the toroid will be zero and the RCD remains in the closed or on position.

As shown in figure 8, when an earth fault occurs, the active and neutral currents are

unequal due to multiple current paths, therefore the magnetic fields produced will also

be unequal. The toroid detects the difference in the magnetic fields and develops a

voltage which is proportional to the leakage current through the earth. If the leakage

current is excessive the tripping mechanism will be operated.

Figure 8

Figure 9 below shows three commonly encountered RCD units.

2-pole, 40A RCD 4-pole, 25A RCD 2-pole, 25A MCB/RCD

Figure 9

RCD’s provide protection against indirect contact by automatically disconnecting the

supply from the affected circuit or circuits. As the current required to trip a RCD is

very _______, it is not dependent on a very low ‘fault loop impedance’ value which is

necessary to operate protective devices such as circuit breakers and fuses.


Page 19 of 181



Refer to clause 1.5.6 – Additional protection by the use of RCDs

Read clauses 1.5.6.1 to 1.5.6.3 and answer the following: 50. RCDs are _______________ as a sole means of basic protection

51. RCDs are recognized as a means of providing ____________________ of

supply (fault protection)

52. RCDs shall be installed for additional protection of the following:

(a) _________________________________

_________________________________

_________________________________

_________________________________ as specified in Clause 2.6

(b) Wiring systems as specified in Clause _____________

(c) Electric heating cables as specified in Clause 4.10.5.

(d) Electrical equipment, including socket-outlets, installed in _______ ______________as specified in Section 6.

(e) Specific electrical installations as specified in AS/NZS 3001, AS/NZS 3002, AS/NZS 3003, AS/NZS 3004, AS/NZS 3012 and AS/NZS 4249.

53. DAMP SITUATIONS – ADDITIONAL SAFETY REQUIREMENTS

A common part of any electrical installation where a person is exposed to the risk of

electric shock is areas that are damp or wet in normal use. Areas such as bathrooms,

swimming pools and spa areas are common areas for people to be in bare feet with

damp or wet skin. These conditions make people more susceptible to electric shock as

a result of reduced body resistance and increased conductivity of building materials

such as concrete floors etc.

Increased conductivity of the body increases the risks of ventricular fibrillation and

respiratory arrest. To reduce the risk, the installation of electrical equipment is

restricted to specialized equipment, defined areas (zones), or prohibited altogether.

Additional protection measures are required in damp situations for equipment that is

permitted to be installed.

Once a clearer understanding is gained on the parameters of damp situations, the

addition protection measures for increased safety will be reviewed.

As protection methods for damp situations will be extensively covered in further units

of stud, the following is provided as a broad overview only.


Page 20 of 181



Refer to clause 1.4.40 – Damp Situation

A damp situation is defined as a situation in which:

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

Refer to Section 6 – Damp Situations and clause 6.1.2 – Selection and Installation

In addition to the requirements of AS3000 sections 1 - 5, electrical equipment used in

damp situations shall be selected and installed to perform the following functions

associated with the proper design, correct construction and safe operation of the

electrical installation:

(a) Provide ___________ ___________ against electric shock in locations where the

presence of _________ or high ____________ present an increased risk.

(b) Provide ___________ protection against damage that might reasonably be

expected from the presence of water or high humidity.

AS3000 defines specific additional requirements for equipment installed in the following

damp situations:

__________________________

__________________________

__________________________

__________________________

__________________________

__________________________

Each of the areas listed above have specifically designated zones that extend in and

around the damp situation. This enables electricians to determine what equipment can

or cannot be installed in damp areas, and what additional requirements will be

required, if any, for that particular area.

In some instances, additional protection will be required by the installation of IP rated

equipment or enclosures. IP is the ‘International Protection’ system of equipment

classification and can be found in appendix G of AS 3000.


Page 21 of 181



17. INTERNATIONAL PROTECTION RATINGS

Refer to AS/NZS 3000 Appendix G – G1 Introduction.

The ‘IP’ rating is usually written as ‘IP’ followed by two numbers and, sometimes, an

additional letter.

The first number, from1 to 6 designates a degree of protection against

___________________________

The second number, from 1 to 8, designates a degree of protection against

___________________________

If a specific degree of protection is not designated, an ‘X’ is used instead of either one

or both numbers. See AS/NZS 3000 figures G1a to G1d below.

IP First number (numeral) – AS/NZS 3000 Table G1a.


Page 22 of 181



IP Second number (numeral) – AS/NZS 3000 Table G1b.

In some cases, an additional letter, from A to D, may be used which designates a

degree of ‘protection of persons against access to hazardous parts’.

On infrequent occasions, a supplementary letter, H, M, S or W, is used to designate

special classes of electrical equipment.

Examples are shown on the following page.


Page 23 of 181



IP rated equipment and enclosures

Figure 10


Page 24 of 181



Examples of IP ratings:

IP44:

(1st numeral is 4) - Does not allow a solid of 1mm diameter to penetrate; and

(2nd numeral is 4) – Provides protection against splashing water from all directions

This socket outlet is rated IP66

(1st numeral is 6)

_________________________________________________

_________________________________________________

(2nd numeral is 6)

_________________________________________________

_________________________________________________

This light fitting is rated IP44

(1st numeral is 4)

___________________________________________________

___________________________________________________

(2nd numeral is 4)

___________________________________________________

___________________________________________________

This IP switch has rubber boots & gaskets & is rated IP56

(1st numeral is 5)

___________________________________________________

___________________________________________________

(2nd numeral is 6)

____________________________________________________

____________________________________________________

This socket outlet has the following specifications:

- It permits a limited ingress of dust with no harmful deposits;

- It permits a limited ingress of water when sprayed from above

at an angle of not more than 60o from the vertical.

Rating is: IP _________

http://www.google.com.au/imgres?q=clipsal+ip66&start=537&um=1&hl=en&sa=N&tbo=d&biw=1440&bih=699&tbm=isch&tbnid=oKBibXqu5hJfcM:&imgrefurl=http://www.electriciansupplies.com.au/shop/index.php?main_page=index&cPath=324_130&docid=LUu8mTIzNpKUcM&imgurl=http://www.electriciansupplies.com.au/shop/images/SO432.jpg&w=383&h=336&ei=Cf4aUYSxHuXomAWTsIDABw&zoom=1&iact=hc&vpx=2&vpy=324&dur=7406&hovh=210&hovw=240&tx=115&ty=126&sig=115287053890372960146&page=12&tbnh=144&tbnw=151&ndsp=55&ved=1t:429,r:46,s:500,i:142

http://www.google.com.au/imgres?q=ip44&start=284&um=1&hl=en&tbo=d&sig=115287053890372960146&biw=1440&bih=699&tbm=isch&tbnid=Ail7hApuLnZctM:&imgrefurl=http://www.toplightco.com/acatalog/Delsin_LED_Outdoor_Light_IP44.html&docid=afV-_PUcZ-GE9M&imgurl=http://www.toplightco.com/acatalog/230824_01.jpg&w=320&h=320&ei=hgIbUZLoDcX4mAXLioHYAg&zoom=1&iact=hc&vpx=894&vpy=145&dur=2453&hovh=225&hovw=225&tx=133&ty=123&page=8&tbnh=142&tbnw=137&ndsp=45&ved=1t:429,r:90,s:200,i:274


Page 25 of 181



Manufacturers of luminaires must abide by the following standard:

AS/NZS 60598.1:2003 Luminaires - General requirements and tests.

The IP requirements for the ingress of water in this standard are set out below. These

strict classifications put on the manufacture of luminaires ensure the effectiveness and

reliability of the IP rating given to luminaires.

It should be noted that luminaires need to be installed in strict accordance to the

manufactures installation instructions to ensure the IP rating remains intact.

Figure 15

An extract from AS/NZS 60598.1:2003 - Symbols


Page 26 of 181



18. CLASSIFICATION OF ZONES FOR DAMP SITUATIONS

The wiring rules sets out areas where equipment is influenced by water or damp

environments. These areas are referred to as zones and it is important to able to

determine which zone you intend to install equipment into, so as any additional

protection requirements can be met.

Barriers, such as screens, doors, curtains and fixed partitions that provide effective

protection against spraying water may be used to limit the extent of a classified zone.

AS/NZS 3000 has a set of comprehensive diagrams in section 6 highlighting each of

these zones for affected damp areas.

When classifying zones, each new zone extends from the boundary of the previous

zone. Zone 0 is the zone directly and most influenced by the damp situation.

For example, zone 0 of a bath or a pool, would be the zone that is actually in the water

container itself; that is, in the bath or pool. Zone 1 would begin at the outer edge of

zone zero and would be the plane extending laterally and vertically around the bath or

pool. The next zone would be around that, and so on.

A simplified diagram is shown in figure 16.

It must be understood that zones are 3 dimensional, and can extend laterally as

well as vertically.

Figure 16


Page 27 of 181



Refer to AS/NZS3000 Table 6.1 and figures 6.1 to 6.11 and answer the following:

Baths, showers & other fixed water containers

a) What is the minimum horizontal distance (↔) that a non I.P.

rated socket outlet may be installed next to a bath?

b) What is the minimum horizontal distance (↔) that a non I.P.

rated light switch may be installed next to a bath?

c) To what horizontal distances (↔) does zone 2 of a bath without a

fixed barrier extend?

d) What is the minimum horizontal distance (↔) that a non I.P. rated

socket outlet may be installed next to a shower screen?

e) To what vertical distances () does zone 2 of a shower base

without a fixed barrier extend?

f) What is the minimum horizontal distance (↔) that a non I.P.

rated socket outlet may be installed next to a hand basin <45L?

g) What is the minimum vertical distance () than a non I.P. rated

socket outlet may be installed above a bathroom floor?

h) What is the minimum horizontal distance (↔) that a non I.P.

rated socket outlet may be installed next to a kitchen sink <45L?

i) What is the minimum horizontal distance (↔) that a non I.P.

rated socket outlet may be installed next to a laundry tub >45L?

Refer to AS/NZS3000 Table 6.2 and figures 6.12 to 6.16 and answer the following:

Pools, paddling pools & spa pools or tubs

a) What area is described as zone 0 of an in-ground swimming

pool?

b) To what horizontal distances (↔) does zone 1 of an in-ground

swimming pool extend from the water’s edge?

c) Is it permissible to install an I.P. 53 rated 10A socket outlet at a

horizontal distance (↔) of 1.5m from the internal rim of the pool

to supply the pool pump? (without further enclosure)

d) Is it permissible to install a 230V light fitting at a horizontal

distance (↔) of 2.1m from the internal rim of the pool?

e) Is a water container with a capacity of 4000L classed as a pool or

a spa?

f) What are the requirements for pool lights installed in zone 0 of a

pool or spa zone?


Page 28 of 181



19. EQUIPOTENTIAL BONDING IN DAMP SITUATIONS

Refer to clause 5.6.2.5 – Showers and bathrooms

Any conductive reinforcing within a concrete floor or wall of a room containing a

shower or bath shall be bonded to the earthing system of the electrical installation.

An equipotential bonding conductor, in accordance with Clause 5.6.3, shall be

connected between the reinforcing material and any part of the earthing system.

The minimum CSA of the equipotential bonding conductor shall be _______mm2

Refer to clause 5.6.2.6 – Swimming and spa pools

The following items shall be equipotentially bonded:

(a) The exposed conductive part of any electrical equipment in the classified pool

zones.

(b) Any ______________________________ of electrical equipment that are not

separated from live parts by double insulation and that are in contact with the pool

water, including water in the circulation or filtering system.

Where any of the items described in Item (a) or Item (b) exist, the bonding

shall be extended to the following additional items:

(i) Any fixed _______________ conductive parts of the pool structure, including the

________________________ of the pool shell and deck.

(ii) Any conductive fittings within or attached to the pool structure, such as pool ladders

and diving boards.

(iii) Any fixed conductive material within arm’s reach of the pool edge, such as

conductive fences, lamp standards and pipe work.

An equipotential bonding conductor, in accordance with Clause 5.6.3, shall be

connected between the bonded parts and the earthing conductor associated with each

circuit supplying the pool or spa, or the earthing bar at the switchboard at which the

circuit originates.

The minimum CSA of the equipotential bonding conductor shall be _______mm2


Page 29 of 181



54. PROTECTION REQUIREMENTS FOR DAMP SITUATIONS

As previously discussed, the risk of electric shock is increased when using equipment

installed in damp situations.

Based on the previous work covered in this section and from the information contained

within section 6 of AS/NZS3000, the additional protection measures that are required

to be used for designated damp areas and zones can be determined.

Refer to section 6 and complete the following table.

Designated Damp Situation as per

AS/NZS3000

Additional Protection method(s) required for the

area (method will be dependent on zone)

Baths, showers and other fixed water

containers

Swimming pools, paddling pools and

spa pools or tubs.

Fountains and water features.

Saunas

Refrigeration rooms.

Sanitization and general hosing-down

operations

*********************************


Page 30 of 181



*****************NOTES*****************

NAME: Practical 3

Page 31 of 181



PROTECTION AGAINST

INDIRECT CONTACT


– REMEMBER –



Practical 3 - Prot. Indirect Contact

Page 32 of 181



************* NOTES *************

.

Section 4

Page 1 of 181Last Updated 02/02/2016

Version 1 UEENEEG063A Section 4 – Earthing

PROTECTION AGAINST

INDIRECT CONTACT

1. The International Protection Rating (IP) indicates the degree of protection ofelectrical equipment enclosures against penetration by:

(a) hazardous gases

(b) solid objects and water

(c) unauthorized persons

(d) flammable liquids and gases

2. The minimum IP rating required for a socket outlet installed in a bathroomwithin the area designated as zone 0:

(a) IPX4

(b) IPX7

(c) IP56

(d) socket outlets are not permitted in Zone 0

3. Underwater pool lighting may be supplied with:

(a) A PELV or SELV supply of 12 V a.c. or less

(b) An SELV system not exceeding 30 V d.c.

(c) An earthing conductor connected to the light

(d) Only a PELV system where the supply is installed close to the light

4. When protection against indirect contact is provided by automaticdisconnection of the supply, what is the maximum disconnection time for –

e) a power circuit with a rating of less than 63A

f) equipment that has only single insulation

g) an electric range

h) a submain.

(a)___________________(b)___________________(c)_____________________

(d)_______________________________ AS/NZS 3000 reference ____________

Section 4 - Earthing

Page 2 of 181 Last Updated 02/02/2016


5. If a “touch voltage” exceeds certain values a protective device must disconnect thesupply. What are the limits of “touch voltage”?

_____________________________________ AS/NZS 3000 reference

____________

6. What are the four acceptable methods for protection against indirect contactspecified in AS/NZS 3000:2007?

____________________________________________________________________

_____________________________________ AS/NZS 3000 reference

____________

7. Protection against indirect contact by automatic disconnection of the supply isachieved by two factors. What are the two factors?

____________________________________________________________________

_____________________________________ AS/NZS 3000 reference

____________

8. Where may socket outlets be installed in a pool zone for the connection of poolequipment?

____________________________________________________________________

_

_____________________________________ AS/NZS 3000 reference ____________

9. Describe one method of supply for luminaires immersed in pool water.

____________________________________________________________________

____________________________________________________________________

___________________________________ AS/NZS 3000 reference _____________

10. State two alternative supply requirements for a circuit that supplies a pool filterpump.

____________________________________________________________________

____________________________________________________________________

___________________________________ AS/NZS 3000 reference ____________


Page 3 of 181



11. Is it permissible to install unenclosed socket outlets within zones 1 or 2 of a bathroom?

___________________________________ AS/NZS 3000 reference ____________

12. Complete the following table. Indicate the minimum IP rating of accessories

permitted in the following locations.

Location IP rating

Within 2 metres of the water of a pool (Zone 1).

External to any building and exposed to the weather.

Appliances in the pool zone but not in contact with the circulating water.

Appliances immersed in the pool water.

A switch installed within 500 mm of a 500 litre spa installed in a bathroom.

13. Complete the following table by determining the minimum horizontal clearance

between a normal socket outlet and the following water containers.

Water Container Distance Reference

Bath.

Washtubs less than 45 litres.

Washtubs over 45 litres.

Spa of 6500 litre capacity.

Spa of 620 litre capacity.




Unenclosed shower rose.

**********NOTES*********


Page 5 of 181



EARTHING

PURPOSE:

In this topic you will analyse safety principles to which electrical systems in

building and premises shall comply.



Define the terms –

o earthed

o earthed situation

o earth electrode

o equipotential bonding

o multiple earthed neutral (MEN) system

o main earthing conductor

o protective earth-neutral (PEN) conductor

o functional earth

o MEN link.

Select minimum size earthing conductors for a range of given activeconductors.

State the operating principle and parts of a multiple earthed neutral system(MEN).

Draw and label the typical arrangement of a MEN system.

Apply AS/NZS 3000 requirements for the selection and arrangement of

protective earthing conductors.

List examples of extraneous conductive parts

Select equipotential bonding conductors for a range of situations

Install a MEN earthing system to suit a single phase domestic installationREFERENCES:

Electrical Wiring Practice. 6th Edition. Petherbridge K & Neeson IVolume 2 - pages 2-16.

Hampson, Jeffery, Electrotechnology Practice, Section 4 and 6, Pearson

Education Australia. French’s Forest NSW 2086

AS/NZS 3000:2007




INTRODUCTION

Although the earthing system does not affect the actual operation of appliances or

equipment, it is the most important part of the installation in its protective role against

the risk of –

______________________________________ and

______________________________________

In an effective earthing system, exposed conductive parts are electrically connected to

the general mass of earth; that is, to the earthing system network in a distribution area.

Refer to AS/NZS 3000 Section 1, clause 1.4 - Definitions.

clause Exposed conductive part:

An exposed conductive part is a part of electrical equipment which –

____________________________________________________________________

____________________________________________________________________

clause - Extraneous conductive part:

An extraneous conductive part is a conductive part that -

__________________________________________________________________

__________________________________________________________________

2 examples of extraneous conductive parts are:

__________________________________________________________________

__________________________________________________________________

An effective earthing system usually ensures that, should a fault occur in an appliance,

sufficient current flows to earth to operate a circuit breaker or fuse and disconnect the

appliance from the supply.

Sometimes a leakage current to earth is insufficient to operate the fuse or circuit

breaker, in which case a residual current device (RCD), if installed, will detect the

leakage current and disconnect the circuit should the leakage be high enough.

To understand how an earthing system operates, you should have knowledge of the

basic principles of the earthing systems and be familiar with the requirements of

Section 5 of the Wiring Rules. Low-voltage installations in Australia and New Zealand

incorporate a MEN earthing system to fulfil these requirements.

when a breakdown of insulation occurs


Page 7 of 181



REASONS FOR EARTHING

A fundamental safety principle of electrical installations is the protection of -

___________________________ and __________________________ against the

danger that may arise from contact with exposed conductive parts which may become

live under fault conditions - known as _______________________ contact.

Earthing also provides _______________________________ and in doing so ensures

the supply actives and neutral are maintained at a fixed potential with respect to earth.

EARTHING TERMS

Refer to definitions: clause - Accessible, readily:

An object is deemed to be readily accessible if it is capable of being reached quickly

and easily and is less than _____________ metres above the ground, floor or platform.

Refer to definitions: clause - Earthed:

Any equipment or conductor which is connected to the_________________________

is deemed to be earthed.

Refer to definitions: clause - Earthed situation:

An earthed situation is anywhere a person may be able to touch exposed conductive

parts and, at the same time, come into contact with earth or any other material that

may provide a path to earth.

Examples of earthed situations include -

all parts of - ____________________, ____________________,

____________________, ____________________.

any outdoor equipment mounted within _________________ metres of the ground

within ____________ metres of the ground, floor or platform in rooms containing

socket outlets, where a person may be able to make simultaneous contact with

exposed conductive parts of equipment and exposed conductive parts of appliances

plugged into socket outlets

within ___________ metres in any direction from a conductive floor, permanently

damp surface, metallic conduit or building materials on which a person may stand.

List three examples of a conductive floor - ____________________________

____________________________

____________________________




MAIN EARTHIG CONDUCTOR

Refer to definitions: clause - Main earthing conductor:

The main earthing conductor is connected between _________________________

__________________________________________________________________

Figure 1

Clause 3.8.1 - Identification - General:

The insulation colour of the main earthing conductor shall be __________________

Refer to Section 5: clause - Minimum size: (of the main earthing conductor)

The minimum allowable size for a copper main earthing conductor is ____________

Refer to Section 5: clause - Resistance of main earthing conductor:

The maximum allowable resistance of a main earthing conductor is _____________

Refer to Section 5: clause - Connection to earth electrode:

When a main earthing conductor is connected to an earth electrode, four

requirements must be satisfied, these are -

_______________________________________________________________

_______________________________________________________________

_______________________________________________________________

_______________________________________________________________

_______________________________________________________________


Page 9 of 181



EARTH ELECTRODE

Refer to Section 5: clause - General:

The connection of the electrical installation earthing system to the general mass of

earth shall be achieved by means of an _______________________________.

Refer to Section 5: clause - Types:

The following types of earth electrode may be used -

______________________________________________________________

______________________________________________________________

______________________________________________________________

Figures 2 and 3 show the requirements in relation to rod and strip earth electrodes.

Strip electrodes must be buried to a minimum depth of ______________________

Refer to Section 5: clause - Location:

In general, earth electrodes shall be located in a position –

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

What is the recommended separation between an earth electrode and other

services such as water, gas, flammable liquid and telecommunications?

__________________________________________________________________

Why is this separation recommended? ___________________________________

__________________________________________________________________




MEN SYSTEM

The abbreviation MEN stands for ________________________________________

Refer to definitions: clause - Multiple earthed neutral system:

The MEN system is created when equipment required to be earthed is connected to

the general mass of earth (via an earth electrode) and is also connected within the

electrical installation to the ______________________________ of the supply

system.

Refer to Section 5: clause - MEN link - General:

The MEN link is a connection at the main switchboard from the main earthing

terminal/connection or bar to the –

__________________________________________________________________

Figure 4

Refer to Section 5: clause - Size:

The MEN link must have a cross-sectional area not less than that of the –

__________________________________________________________________

Where consumers’ mains are not protected on the supply side by short circuit

protective devices the MEN link shall have a cross-sectional area not less than that

of the _____________________________________________________________

Refer to Section 5: clause - Identification:

If the MEN link is insulated, the insulation shall be coloured ___________________


Page 11 of 181



PROTECTIVE EARTHING CONDUCTORS "the earth in the twin & earth"

Refer to definitions: clause - Protective earthing conductor:

A protective earthing conductor is a conductor used to connect any portion of the

earthing system to the portion of the electrical installation required to be earthed.

Figure 5

Refer to Section 5: clause - Protective earthing conductor - General:

Any ______________________________________ shall be connected to the

earthing system via a protective earthing conductor.

Protective earthing conductors shall be connected to -

an earthing terminal/connection or bar at the ___________________________

any point on the _________________________________________________

an earth terminal or bar at a ________________________________________

any point on a ___________________________ earthing conductor.

Refer to AS/NZS 3000 Figure 5.3 for examples of earthing connections.

Refer to Section 5: clause - Conductor material and type - General:

When copper earthing conductors are used they shall be of high conductivity copper

and can be in the form of -

________________________ conductors; or

________________________ conductors; or

________________________ conductors having a CSA of not less than 10mm2

and a thickness of not less than 1.5mm2 .



Version 1 UEENEEG063A Section 4 – Earthing .

Refer to Section 5: clause - Size - General:

The cross-sectional area of a protective earthing conductor shall ensure -

adequate ________________________________ for prospective fault currents

for a time at least equal to the operating time of the associated protective device

NOTE: Prospective fault current means the highest possible fault current that could flow at the

point of a fault or the maximum fault current that would flow in the worse possible instance. ie:

when the impedance at the fault is at its lowest possible value.

appropriate ______________________________________________________

adequate ___________________ strength and resistance to external influences

allowance for deterioration in ________________ that may be reasonably be

expected.

Refer to Section 5: clause - Selection of CSA of protective

earthing conductor:

The CSA of protective earthing conductors shall be determined -

by calculation using clause __________________

and

shall be not less than the appropriate value shown in table _________.

Example: 1

Select the minimum size protective earthing conductors for the conditions shown

below.


Page 13 of 181


UEENEEG063A Section 4 – Earthing Version 1 Disclaimer: Printed copies of this document are regarded as uncontrolled.

Refer to Section 5: clause - Types - General:

List 5 types of protective earthing conductor that may be used to earth exposed

conductive parts –

earthing conductors that are ________________________________________

earthing conductors in a ___________________________________________

earthing conductors in _____________________________________________

__________________

_______________________________________________________________

and similar wiring enclosures.

Can sprinkler pipes, gas pipes, water pipes or other metallic non-electrical service

enclosures be used as earthing conductors?

__________________________________________________________________

Example: 2

Complete table 2 by determining the type of earthing method that may be used in

conjunction with each of the listed installation methods.




Refer to Section 5: clause - Special conditions:

List two requirements that apply when metallic conduit or trunking is used as a

protective earthing conductor.

_______________________________________________________________

_______________________________________________________________

_______________________________________________________________

_______________________________________________________________

Fixed and hinged components of metallic framework such as cubicle doors are

deemed to be earthed provided that –

_______________________________________________________________

_______________________________________________________________

and

_______________________________________________________________

_______________________________________________________________

Refer to Section 5: clause - Continuity - General:

Protective earthing conductors shall be suitably protected against –

__________________________________________________________________

__________________________________________________________________

Metallic wiring enclosures, metallic sheaths, armours and screens of cables that are

required to be earthed or used as an earthing medium must be -

_________________________ and _________________________ continuous.

Refer to Section 8: clause - Continuity of earthing system:

The resistance of protective earthing conductors shall be low enough to permit the

passage of current necessary to operate the circuit ________________________.

NOTE: Protective devices must safely operate within required times as set out in clause 5.7.2


Page 15 of 181



The maximum resistance of the protective earthing conductor associated with any

particular circuit depends on -

___________________________________________ of the protective device

and the

_________________________ of the live conductors that comprise the circuit.

FUNCTIONAL EARTH CONDUCTOR

Refer to definitions: clause - Functional earthing:

Functional earth conductors are used to ensure the correct operation of electrical

equipment. Functional earth conductors are commonly found in -

________________________________________ equipment;

________________________________________ equipment;

________________________________________.

NOTE: Clause 5.7.2 states that functional earth conductors should NOT be green or green/yellow so as not to confuse them with protective earth conductors. Functional earth conductors are typically white, but can vary.

Example: 3

Identify the type earthing conductors shown in figure 6.




EARTHING OF ELECTRICAL EQUIPMENT – PROTECTIVE EARTHING

Refer to Section 5: clause - Earthing of equipment - General:

Refer to Section 5: clause - Exposed conductive parts

Except where exempted, exposed conductive parts of electrical equipment shall be

earthed where the electrical equipment is -

a) __________________________________________________________________

b) __________________________________________________________________

__________________________________________________________________

__________________________________________________________________

Exceptions:

Electrical equipment need not be earthed where it complies with any of the following

provisions:

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

Refer to Section 5: clause - Particular electrical equipment -

Wiring systems:

The exposed conductive parts of wiring enclosures or conductive sheaths, armours or

screens required to be earthed, shall be earthed at the -

__________________________________________________________________

A metallic screen or braid incorporated in a cable need not be earthed where -

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

Additionally, metallic cable sheathing, armouring, screening or braiding need not be

earthed if the requirements of clause _______________ are met.


Page 17 of 181



Refer to Section 5: clause - Earthing of equipment supplied by

flexible cord or cable:

The exposed conductive parts of electrical equipment supplied by flexible cords or

cables shall be earthed by connection to a protective earthing conductor:

_____________________________________________________________________

Refer to Section 5: clause - Socket-outlets:

The earthing contact of every socket-outlet shall be earthed except:

_________________________________________________________________

_________________________________________________________________

_________________________________________________________________

_________________________________________________________________

Refer to Section 5: clause - Lighting points:

A protective earthing conductor, connected to a terminal or suitably insulated and

enclosed, shall be provided -

_____________________________________________________________________

_____________________________________________________________________

A protective earthing conductor shall not be provided for -

_____________________________________________________________________

_____________________________________________________________________

List four types of lighting points that need not be earthed:

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________




Refer to Section 5: clause - Unprotected consumers mains:

NOTE: The definition of unprotected consumers’ mains may vary between electricity

distributors. Local service rules should be checked with the relevant distributor.

Any metallic equipment associated with unprotected consumers mains shall be

earthed by connection to the:

__________________________________________________________________

or

__________________________________________________________________

Provide four examples of metallic equipment that may required to be earthed when

associated with unprotected consumer’s mains.

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

Refer to Section 5: clause - Conductive supports for aerial

conductors:

Supports for low voltage aerial conductors such as metallic poles, posts, struts,

brackets and stay wires shall be earthed when within __________________________

Refer to Section 5: clause - Structural metalwork including

conductive building materials:

Parts of structural metalwork, including conductive building materials, shall be earthed

where -

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

The breaking of a conductor at a termination shall not result in contact between

unearthed conductive building material and -

__________________________________________________________________

__________________________________________________________________


Page 19 of 181



Refer to Section 5: clause – Domestic electrical installations

__________________________________________________________________

Clause 5.4.6.3 - Connection to protective earthing conductors, further states that

the earthing of structural metalwork and building materials may be affected by the

connection of a protective earthing conductor (of appropriate size) at one point of the

metalwork provided that the:

__________________________________________________________________

__________________________________________________________________

EQUIPOTENTIAL BONDING

Refer to definitions: clause -Equipotential bonding:

Equipotential bonding conductors are used to minimise the risk of potential differences

occurring between exposed conductive parts and extraneous conductive parts of an

installation. Equipotential bonding conductors are not intended to carry current in

____________________________________.

Refer to Section 5: clause - Arrangement:

Bonding shall be arranged by the connection of the extraneous conductive parts to the

earthing system of the installation by equipotential bonding conductors in accordance

with clauses ____________________________________.

Refer to Section 5: clause - Insulation and identification:

Equipotential bonding conductors shall be coloured ___________________________.

Refer to Section 5: clause - Conductive water piping:

Under what two conditions shall metallic water piping be equipotentially bonded?

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

When conductive water piping is bonded -

To which conductor must the equipotential bond connect? ___________________

Where is the connection of the bond to be made? __________________________

__________________________________________________________________




Figure 2

Refer to Section 5: clause - Other Conductive piping systems:

Provide four examples of metallic piping that must be bonded if in contact with the

exposed metallic parts of wiring enclosures or electrical equipment.

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

Refer to Section 5: clause - Conductive cable sheaths and

conductive wiring enclosures:

Where metal sheaths, armours or wiring enclosures are in contact with pipes

containing ______________________________________________they shall be

bonded to prevent voltage differences at points of contact.

Refer to Section 5: clause - Showers and Bathrooms:

Any ________________________________ within a concrete floor or wall forming

part of a shower or bathroom shall be bonded to the earthing system of the electrical

installation.


Page 21 of 181



Refer to Section 5: clause - Swimming and spa pools:

List the items to be equipotentially bonded around swimming and spa pools.

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

If any of the above items exist, the bonding must be extended to:

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

Refer to Section 5: clause - Telephone and telecommunications

earthing systems:

Telecommunications earthing systems may be connected in common with the

electrical installation earthing system in order to:

__________________________________________________________________

__________________________________________________________________

If the telecommunications earthing system is bonded to the installation earthing

system it shall be connected:

_________________________________________________________________

_________________________________________________________________

_________________________________________________________________

_________________________________________________________________




If an enclosed terminal is used to provide the point of connection, the following

conditions shall apply:

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

Refer to Section 5: clause - Size (minimum cross-sectional area):

Provide the minimum size (CSA) of equipotential bonding conductors for the following

situations:

Metallic water piping: ..................................................................................._____ mm2

Metallic fire sprinkler, gas or flammable liquid pipes: ................................. _____ mm2

Metallic cable sheaths and wiring enclosures in contact with pipes containing

flammable liquids or gases: ........................................................................ _____ mm2

Metallic parts of swimming and spa pools: ................................................. _____ mm2

Telecommunications earthing systems: ....................................................... _____ mm2

Metallic enclosures and supports associated with unprotected consumers mains:

_____________________________________________________________________

_____________________________________________________________________

MEN SYSTEM – TYPICAL ARRANGEMENT OF CONDUCTORS

Refer to clause - Earthing in outbuildings:

Outbuildings such as work sheds, detached garages, granny flats, etc. can be earthed

in one of two ways, the outbuilding may be:

connected via a protective earthing conductor to the main building or

regarded as a separate installation and have its own MEN connection and earth

electrode.


Page 23 of 181



Read and summarise the requirements that must be followed when installing a

separate MEN point.

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

__________________________________________________________________

Example: 3

If a detached granny flat is supplied from the main house with a metallic water pipe, list

the methods available to earth the distribution board in the granny flat.

_____________________________________________________________________

_____________________________________________________________________

____________________________________________________________________

Example: 4

If a group of 8 villas is supplied with a non-metallic water service, list the methods

available to earth the distribution boards in each villa.

_____________________________________________________________________

_____________________________________________________________________




Example: 5

In the electrical installation represented in figure 3, outbuilding 2 is to be supplied from

outbuilding 1 and both outbuildings are to have a separate MEN installed. Show an

acceptable arrangement of supply and earthing by drawing in the supply and

protective earthing conductors.

Figure 3


Page 25 of 181



Example: 6

On the arrangement shown in figure 4, draw a wiring diagram for a MEN earthing

system. On the diagram -

(a) identify the items labelled (a), (b) and (c)

(b) identify the type and size of each conductor given the consumers mains are

16mm2 and deemed as unprotected.

Figure 4




Example: 7

Using the arrangement shown in figure 5, draw a wiring diagram for a MEN earthing

system.

On the diagram identify the size of each conductor given the consumers mains are

35mm2 and deemed as unprotected.

Figure 5


Page 27 of 181



Example: 8

On the figure 6 below: a) Identify each of the 13 parts indicated using the correct terminology

b) With the assistance of your teacher, draw the fault current path (earth fault loop) using

a highlighter or coloured pen assuming an active to earth fault on the single power

point.

Note: Earth fault loop and fault current values will be discussed in further sections.

Figure 6




*************** NOTES ***************

NAME: Practical 4

Page 29 of 181



EARTHING

PURPOSE:

This practical assignment is designed to examine a MEN system and enable students

to select and installed the correct system parts required to meet the requirements of

the AS/NZS 3000 standards. In addition, the method of measuring earth fault loop

impedance is examined for final sub-circuits not protected by a RCD.

At the end of this practical assignment the student will be able to:

Select correct earthing conductor types and sizes to complete a domestic

MEN system for an installation supplied by 16mm2 S.D.I consumers mains.

Draw and label a MEN system

Install a MEN system by the means of a main earthing terminal/bar.

Terminate earthing conductors as required.

Test a MEN system for satisfactory connections, continuity and resistance.

Test the earth fault loop impedance of a final sub-circuit and verify it meets

the requirements of AS/NZS 3000.

EQUIPMENT:

1mm2 and 2.5mm2 T&E TPS cables

4mm2 , 6mm2 and 16mm2 green/yellow earth wire

16mm2 Black building wire

16/6 earth lug and crimp tool

Earth clips for electrode and water pipe bond

Masking Tape

Digital Ohmmeter

Insulation tester


Page 30 of 181



1. CABLE SIZE and WIRING DIAGRAM

On the diagram below, draw the connections for a MEN system using a main earth

terminal/bar connection. Label the size AND type of earthing conductor for the following:

(a) The consumer mains active and neutral conductors (16mm2 SDI - unprotected)

(b) The Main Neutral for the Customer Neutral link

(c) The MEN link

(d) The Main earth conductor

(e) The water pipe equipotential bond

(f) Sub-circuit earth conductors

(g) Sub-circuit neutral conductors (assume circuits are protected by RCD combo’s,

therefore terminate neutrals in the customer neutral link)

Metallic meterbox

enclosure

Conductive

water piping

Earth Electrode

Section 4 – Earthing

Page 31 of 181



2. MEN SYSTEM INSTALLATION

(a) Connect a ______ mm2 green yellow protective earth conductor between themetal box and one end of the earth link. Use a lug at the box end.

(b) Install a ______ mm2 main earth and a ______ mm2 water pipe bond and connect to the earth electrode and water pipe.

(c) Install final subcircuit tails and connect the neutrals to the neutral link. (Leave the active conductors the same length as the corresponding neutral conductors but leave them un-terminated to one side)

(d) Connect subcircuit earth tails of _____ mm2, _____ mm2 & _____ mm2 to the main earth link.

(e) State the method as set out in AS/NZS 3000 for the testing of a final sub-

circuit not protected by an RCD. (Check section 8 – testing)

_______________________________________________________________

_______________________________________________________________

_______________________________________________________________

_______________________________________________

_______________________ AS/NZS 3000 reference: _______________

(f) With guidance from your teacher, label the appropriate parts of the switchboard

as required for a MEN system.

Note: Use masking tape on your switchboard. DO NOT label the panel directly

(g) Have the teacher inspect the work. ____________

3. MEN SYSTEM AND LOOP IMPEDANCE TESTING

MEN SYSTEM TEST RESULTS RESULT / COMMENT

Connection integrity of lugs, clips, bars etc.

Continuity of earth conductors

Resistance measurement of main earth and bond

Loop impedance of the Hot Water circuit

Labelling of necessary parts


Page 32 of 181



Section 4 – Earthing

Page 33 of 181



*************** NOTES **************.


Page 34 of 181



*************** NOTES **************

Section 5

Page 1 of 181


UEENEEG063A Section 5 – OL & SC Protection Version 1 Disclaimer: Printed copies of this document are regarded as uncontrolled.

EARTHING

A situation where there is a chance of a person touching an exposed conductive part

and at the same time coming in contact with earth is referred to as an ____________

situation.

AS/NZS Clause no. ___________________

Copper earthing conductors of 1mm2 and 1.5mm2 shall only be used in what

form?_______________________________________________________________

AS/NZS Clause no. ___________________

Why is it necessary to maintain a separation of at least 0.5 metres between an earth

electrode and buried metallic services? ____________________________________

AS/NZS Clause no. ____________________

Where consumers mains are not protected on the supply side by short circuit protective

devices, the MEN link shall have a CSA of ________________________

___________________________________________________________________

AS/NZS Clause no. ____________________

The resistance of the main earthing conductor shall not exceed? ________________

AS/NZS Clause no. ____________________

At what point should steel conduit be earthed when enclosing a single insulated circuit?

_____________________________________________________________

AS/NZS Clause no. ____________________

A metal control panel (electrical equipment) is located outside an earthed situation but is

supplied with a metallic conduit which passes through an earthed situation. Is it

necessary to earth the control box? _______________________________________

AS/NZS Clause no. ____________________

Section 5 – OL & SC Protection

Page 2 of 181


Version 1 UEENEEG063A Section 5 – OL & SC Protection .

Which of the following metallic parts shall not be used as a protective earthing conductor?

a) Metallic sheaths, armours and screening

b) Metallic conduits, tubes or trunking

c) Sprinkler pipes or pipes conveying gas or water

d) Metallic framework for mounting electrical equipment

AS/NZS Clause no. ____________________

Is it necessary to mark the terminals for the connection of the MEN connection and the

main neutral conductor on the main neutral link? _________________________

AS/NZS Clause no. ____________________

What identification is required at the connection between the main earth and the earth

stake? _________________________________________________________

___________________________________________________________________

AS/NZS Clause no. ____________________

What is the minimum CSA of any equipotential bonding conductor that may be required

in an installation? _________________________

AS/NZS Clause no. ____________________

In general, is a protective earth cable required to be installed at a batten holder or light

point if the light point is non conductive? _______________________________

AS/NZS Clause no. ____________________

**********************************


Page 3 of 181



PROTECTION AGAINST OVERLOAD AND SHORT CIRCUIT CURRENT

PURPOSE:

This section examines the causes of overload and fault currents within an electrical

installation. The meaning of and the determination of fault currents is also covered.

Additionally, the requirements of AS/NZS 3000:2007 in relation to the selection of

protective devices will be examined.



a) explain how overload current or fault currents may occur in an electrical

installation

b) determine the level of fault current possible at a given point in an installation

from cable impedances and data from the electricity supplier

c) determine which methods and devices comply with AS/NZS 3000 for

providing protection against the damaging effects of overload and fault

current

d) select protection devices for protection against overload currents

e) select protection devices for protection against fault currents.

REFERENCES:

f) Electrical Wiring Practice. 6th Edition. Petherbridge K & Neeson I

Volume 2 pages 20-42.

g) Electrotechnology Practice. 1st Edition. Hampson J

Pages 20 and 199-203


Page 4 of 181



H) INTRODUCTION

Electrical wiring and equipment is vulnerable to many service conditions that could

affect its efficient operation. Some of these conditions are associated with the

working environment of the equipment, others relate to the effects of electric current

within a circuit.

All conductors and items of electrical equipment have certain limiting factors, one of

these factors is the maximum safe working current or as it is commonly called the -

i) ____________________________________; or

j) ____________________________________.

The current carrying capacity of a conductor or piece of equipment is the maximum

current that can be carried on a continuous basis without any detrimental effects to

the conductor or equipment.

If the specified current limits are exceeded and there is no protection, or if the

protection is either inadequate or ineffective, the resulting abnormal conditions could

produce -

k) _____________________________ of conductors; and

l) subsequent insulation ____________________________.

Insulation failure is caused by excessive power loss occurring within the conductors.

As previously discussed, heating effect is proportional to the square of the current, so

a 100% overload (double the normal circuit current) will result in a heat loss four

times higher than that for a normal load over the same time period –

H = I2.R.t Joules

To ensure that wiring operates within its current-carrying capacity, devices are

employed for the protection of a circuit against current overcurrent. The most

commonly used overcurrent protective devices are the -

m)________________________________; and

n) ________________________________.


Page 5 of 181



If the overload is large, as would occur with a short circuit, the protection must be

capable of interrupting the fault current before it can rise to a dangerous value. The

protection must also be able to disconnect the supply to the fault without damage to

itself. To achieve this, the protection must have adequate _____________________

capacity. Known as -

o) ____________________ capacity for circuit breakers

and

p) ____________________ capacity for fuses.

Q) CURRENTS

Refer to Clauses 1.4.37, 1.4.38, 1.4.39 and 1.4.70

The Wiring Rules defines four types of current -

r) overcurrent

s) overload current

t) fault current

u) short-circuit current.

Diagrammatically, these currents may be represented as shown in figure 1.

Figure 1

Overcurrent A current exceeding

the rated value

Overload current An overcurrent in an

Electrically sound circuit

Fault current Results from an insulation failure

or the bridging of insulation

Short circuit current A fault current flowing

between live conductors


Page 6 of 181



V) OVERCURRENT

Refer to clause 1.4.70 - Overcurrent:

The Wiring Rules defines an overcurrent as a current ________________________.

Based on the Wiring Rules, what is the rated value for conductors?

The rated value is the _________________________________________________.

Refer to clause 1.5.9 - Protection against overcurrent:

Protection against overcurrent may be provided by either of two methods -

w) ________________________________________________________________

x) ________________________________________________________________

Refer to Clause 2.5.1 - General:

__________________ conductors shall be protected by one or more devices that

automatically disconnect the supply in the event of overcurrent, before the

overcurrent attains a magnitude or duration that could cause –

y) __________________________________________________________ or

z) __________________________________________________________ or

aa) __________________________________________________________.

Protection against overcurrent shall consist of protection against -

bb) ______________________________ and

cc) ______________________________.

Refer to Clause 2.5.1.2 – Submains and final subcircuits

An overcurrent protective device or devices ensuring protection against overload

current and short circuit current shall be placed at the

dd) ____________________ of every circuit and at each point where a

ee) _________________________ occurs in the current carrying capacity of

conductors.

See figure 2 on the following page.


Page 7 of 181



AS/NZS 3000:2007

An overcurrent protective device or

devices ensuring protection against

overload current and short-circuit

current shall be placed at the origin

of every circuit and at each point

where a reduction occurs in the

current carrying capacity of the

conductors

Figure 2

Refer to Clause 2.5.2 – Devices for protection against both overload and short circuit

currents.

Protective devices providing protection against both overload and short circuit current

shall be capable of breaking any overcurrent up to and including the _____________

___________________________________ at the point where the device is installed.

FF) OVERLOAD CURRENT

Refer to Clause 1.4.38 – Current, overload

An overload current is an overcurrent occurring in a circuit that is _______________

__________________.

Refer to Clause B3.1 - General

Overload protective devices usually have an ______________________________

characteristic.

The protection of conductors by

protective devices is shown

graphically in figure 3.

Figure 3


Page 8 of 181



The conductor is deemed to be

protected if its damage curve is to

the ________________ of the

time/current characteristic curve of

the protective device.

Figure 3 a

Refer to Clause 2.5.3.1 – Coordination between conductors and protective devices

The operating characteristics of a device protecting a conductor against overload

shall satisfy the following two conditions –

Circuit Breaker HRC Fuse

Coordination

Overload protection


Page 9 of 181



Example 1:

A circuit with a maximum demand of 15A is to be protected by a miniature circuit

breaker. Determine each of the following values -

a) maximum demand of the circuit, IB = __________

b) minimum acceptable current rating for the circuit breaker, IN = __________

c) minimum acceptable current carrying capacity for the circuit cable, IZ = __________

d) minimum current required to make circuit breaker trip, I2 = ________________

Does the circuit arrangement provide correct coordination of the load, protective device and cable?

______________________________________________________________________

______________________________________________________________________

Does the circuit arrangement provide adequate overload protection?

______________________________________________________________________

______________________________________________________________________

Example 2:

A circuit with a maximum demand of 15A is to be protected by a fuse. Determine each

of the following values -

a) maximum demand of the circuit, IB = __________

b) minimum acceptable current rating for the fuse, IN = __________

c) minimum acceptable current carrying capacity for the circuit cable, IZ = __________

d) minimum current required to make the fuse operate, I2 = ________________


______________________________________________________________________

______________________________________________________________________

Does the circuit arrangement provide adequate overload protection?

_____________________________________________________________________

_____________________________________________________________________


Page 10 of 181



Example 3:

A 2.5mm2, copper, 2-core and earth, insulated and sheathed flat cable supplies a

4.8kW, 240V hot water system. The circuit is protected by a circuit breaker.The cable

is installed in non-metallic conduit in air and has a current carrying capacity of 22A.

Note: The current carrying capacity is determined using AS/NZS 3008.

Determine the following -

(a) Maximum demand current (IB) ______________________________________

(b) Nominal current of circuit protective device (IN) _________________________

(c) Current carrying capacity of cable (IZ) ________________________________

(d) Current ensuring operation of protective device (I2) ______________________


_____________________________________________________________________

Does the circuit arrangement provide adequate overload protection? ______________

GG) SHORT-CIRCUIT CURRENT

Refer to Clause 1.4.39 - Current, short-circuit

A fault resulting from a fault of ________________ impedance between ____________

conductors having a difference in potential under normal operating conditions. The fault

path may include the path from active via earth to neutral.

This current is also referred to as __________________________________________.

Short circuits may occur between –

hh) __________________________________________

ii) __________________________________________

jj) __________________________________________

Refer to Clause 2.5.4.1 – Determination of prospective fault current

The prospective short-circuit current at every relevant point of the electrical

installation shall be determined either by _____________________ or measurement.

Devices used for protection against short circuit currents may be –

_________________________________________________________________; or

_________________________________________________________________.


Page 11 of 181



The NSW Service and Installation Rules, figure 4, provide nominal prospective short-circuit currents at the point of supply. The details are as follows.

Refer to Clause 2.5.4.5 – Characteristics of short-circuit protective devices

The breaking capacity shall be not less than the ______________________________ at the point where the devices are installed.

However, a lower capacity protective device is permitted provided another protective device (having the required breaking capacity) is installed on the _________________ ________________________.

These devices are known as ________________________________________.

Figure 4


Page 12 of 181



All currents caused by a short-circuit occurring at any point of a circuit shall be interrupted before the temperature of the conductors reaches the permissible limit.

For short-circuits of duration up to 5 s, the time in which a given short-circuit current will raise the conductors from the highest permissible temperature in normal duty to the limit temperature may, as an approximation, be calculated from the following equation:

where: t = duration in seconds K = factor dependent on the material of the conductor, the insulation

and the initial and the final temperatures S = cross-sectional area of the conductor in mm2

I = effective short-circuit current in amps (r.m.s)

Example 4 :

For 16 mm2 consumers mains (V75 copper conductors at 40ºC ambient temperature)

installed in a domestic installation, the time taken for the cable to reach the maximum

allowable temperature under short-circuit conditions is:

K = 111 (copper conductor with PVC insulation)

S = 16mm2

I = 10kA

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

Example 5:

A single-phase final subcircuit supplying 10A socket outlets consists of 2.5 mm2

copper active conductors and a 2.5 mm2 copper earthing conductor. The circuit is

protected by a 20A type C circuit breaker. If a short-circuit of 450A occurred at the

terminals between active and neutral of a socket outlet, determine whether the circuit

breaker protecting the circuit will operate in the required time. Assume K factor is 111,

ambient temperature is 40°C and insulation is PVC.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________


Page 13 of 181



KK) EARTH FAULT LOOP

Refer to AS/NZS 3000 Section 1 definitions for ‘Earth Fault Loop Impedance’.

Earth fault loop impedance is the impedance of the ___________________________

____________________________________________________________________

Figure 4A below has been extracted from AS/NZS 3000 appendix B and shows a

simplified Earth-Fault loop path. When current flows through the secondary of the

transformer windings, it travels the length of the closed circuit through all the

associated cables, components and final sub-circuits before returning to the

transformer via the neutral conductor (conventional current flow).

Figure 4A

Figure 5 on the following page also displays the Earth-Fault loop but in a manner

referred to as the ‘Equivalent Circuit’ for Earth-Fault loop. It highlights a simple series

circuit showing the resistive values of all the components that make up the fault path

for ease of understanding.


Page 14 of 181



LL) CALCULATION OF PROSPECTIVE FAULT CURRENTS

In order to calculate the prospective fault current at various points in an installation two

parameters need to be known, the -

voltage at the source

and

impedance of the path.

Figure 5 shows the ‘equivalent circuit’ of an earth-fault loop diagram of a distribution

transformer supplying a single phase electrical installation. For simplicity the cable and

transformer impedances have each been assumed to be equal to 0.1.

Figure 5

For the arrangement shown in figure 5 determine the –

(a) load current under normal operating conditions

_________________________________________________________________

(b) prospective fault current if a short-circuit occurs between points e and f

_________________________________________________________________

(c) prospective fault current if a short-circuit occurs between points d and g

_________________________________________________________________

(d) prospective fault current if a short-circuit occurs between points c and h

_________________________________________________________________

(e) prospective fault current if a short-circuit occurs between points b and i

_________________________________________________________________

(f) prospective fault current if a short-circuit occurs between points a and j

_________________________________________________________________

12

Distribution Consumer

mains Sub

main Final

subcircuit

a b c d e

f g h i j 0.1

0.1

0.1 0.1 0.1

0.1 0.1 0.1 0.1

Load Transformer

230V


Page 15 of 181



Based on the results from the circuit of figure 8, what can be said about the size of

the fault current the closer you are to the supply source?

_____________________________________________________________________

Figure 6 shows a simplified layout of an electrical installation and its respective fault levels.

Figure 6

For the arrangement shown in figure 6, list the fault levels in order, commencing with

the highest and finishing with the lowest.

mm) ______________________________

nn) ______________________________

oo) ______________________________

pp) ______________________________

If a 240V, single pole, 20A type C circuit breaker was to be installed on each

switchboard shown in figure 6, what would be the likely differences between the three

circuit breakers?

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

Details of the voltage source (supply transformer) are usually stated in terms of:

qq) source impedance as a percentage of the primary-rated voltage

(400V/230V, 500kVA, impedance = 5%) or

rr) fault level in volt-amperes, usually in MVA

(400V/230V, 500 kVA, fault level = 10MVA) or

ss) prospective fault current in amperes/phase, usually in kA

(400V/230V, 500 kVA, fault current 14.4 kA)

Main switchboard

Distribution Board 1

Distribution Board 2

Final subcircuit Consumer

mains

Fault level 1

Fault level 2 Fault

level 3

Fault level 4


Page 16 of 181



Based on the work covered in previous units -

Three phase transformer rating, measured in VA, is given by -

Transformer rated current, measured in amperes -

Transformer impedance, measured in ohms –

Fault level at the transformer secondary terminals, measured in VA

Fault current, measured in amperes -


Page 17 of 181



Example 6:

Given a 400/230V, 600kVA transformer has an impedance of 4%, determine the -

a) rated current

b) fault level at the transformer secondary terminals

c) fault current at the transformer secondary terminals

d) transformer impedance in ohms.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

____________________________________________________________________

Example 7:

A 400/230V, 500kVA transformer has a nominated fault level of 10MVA, determine

the -

a) prospective fault current at the transformer

b) transformer impedance in ohms.

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

Example 8:

A 400/230V, 500kVA transformer has a prospective fault current of 14.4kA, what is

the impedance per phase of the transformer?

_____________________________________________________________________

_____________________________________________________________________

____________________________________________________________________


Page 18 of 181



Example 9:

For the arrangement shown in figure 7 determine the -

a) fault level at the supply source

b) prospective fault current at the source

c) ohmic impedance of the source

d) prospective fault current at the switchboard

e) prospective fault current at the load.

Figure 7

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

Voltage source Switchboard Load

400/230V 500kVA %Z = 5%

0.0441 0.4066


Page 19 of 181



Supply transformer

Main switchboard

Distribution board

400/230V 500kVA Z = 0.016

Consumer mains

Z = 0.004

Submain

Z = 0.03

Example 10:

For the supply system shown in figure 8, determine -

a) rated secondary current of the transformer

b) fault current at the transformer secondary terminals

c) fault current at the main switchboard

d) fault current at the distribution board.

Figure 8

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________

_____________________________________________________________________


Page 20 of 181



TT) PROTECTION OF WIRING

Based on the material covered thus far, the requirements for the protection of wiring

may be summarised as follows:

uu) the fuse or circuit breaker should be capable of carrying its rated current

continuously without overheating or deterioration.

vv) small overloads of short duration should not cause the protection to operate.

ww) the protection must operate, even on a small overload, if the overload persists

long enough to cause overheating of the circuit conductors.

xx) the protection must open the circuit before damage caused by fault currents

can occur.

yy) the protective device must have sufficient short circuit capacity to break and

clear the fault without being damaged.

zz) protection must be 'discriminative' in that only the faulty circuit is isolated and

other circuits remain operative and unaffected

********************************


Page 21 of 181



*************** NOTES ***************

NAME: Practical 5

Page 22 of 181





– REMEMBER –



T6 – OL & SC Protection

Page 23 of 181



********** NOTES **********

.

Section 7

Page 1 of 181


UEENEEG063A Section 7 – Over & Under Voltage Version 1 Disclaimer: Printed copies of this document are regarded as uncontrolled.


The term ‘over-current’ is defined as_______________________________________

___________________________________________________________________

AS/NZS Clause no. ____________________

What is the meaning of ‘overload current?__________________________________

___________________________________________________________________

AS/NZS Clause no. ____________________

What is a short circuit current?___________________________________________

___________________________________________________________________

___________________________________________________________________

AS/NZS Clause no. ____________________

All currents caused by a short circuit shall, shall be interrupted before the temperature of

the conductors reach what limit? _____________________________

AS/NZS Clause no. ____________________

What are the four ways of providing protection against both overload currents and short

circuit current?

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

AS/NZS Clause no. ____________________

Section 7 – Over & Under Voltage

Page 2 of 181 Version 1 UEENEEG063A Section 7 – Over & Under Voltage


10

Distribution Consumer

mains Sub

main Final

subcircuit

a b c d e

i 0.005 h 0.04 g 0.1 f

j

0.015

0.004

0.04 0.1 0.005 0.004

Load Transformer

230V

To adequately protect a cable from the heating effects of an electric current, a fuse must

operate within conventional time with a prescribed value of current. What is the value of

current that ensures effective operation of a 20 Amp fuse?

______________________________________________________________________

AS/NZS Clause no. ____________________

Electrical equipment which is double insulated is defined as being class ___________?

AS/NZS Clause no. ____________________

If a cable rated at 20A is overloaded to 40A, the extra value of the heating effect is

_____________ times greater than the original value.

AS/NZS Clause no. ____________________

Refer to figure 9 below and determine the following:

(a) load current under normal operating conditions ____________________________

__________________________________________________________________

(b) prospective fault current if a short-circuit occurs across the load.

_________________________________________________________________

(c) prospective fault current if a short-circuit occurs between points b and i

__________________________________________________________________

(d) An appropriately rated circuit breaker (minimum current AND kA rating). Explain.

_________________________________________________________________

_

_________________________________________________________________

_


Page 3 of 181



Figure 9


Page 4 of 181


Version 1 UEENEEG063A Section 7 – Over & Under Voltage .

The figure below represents the current-time characteristics of three circuit protection

devices identified as A, B and C. The heating characteristic of the cable is also shown.

Use this information to answer the following questions.

(a) Which of the circuit protection devices (A, B or C) is the most suitable to protect the

cable if the fault current was 30A? ______________________________________

(b) Which of the circuit protection devices (A, B or C) will disconnect the circuit before a

current of 200A would damage the cable?________________________________

(c) The three characteristic curves (A, B and C) represent three different types of current protection devices. Write in the space below the identifying letter for each characteristic curve that matches the appropriate type of device.

Protection device Letter

Fuse

Magnetic trip circuit breaker

Thermal trip circuit breaker

Combined thermal/magnetic trip circuit breaker

Residual current device

************* NOTES *************


Page 5 of 181



PROTECTION AGAINST OVER VOLTAGE AND UNDER VOLTAGE

PURPOSE:

In this topic you will analyse safety principles to which electrical systems in

building and premises shall comply.



explain the causes of overvoltage and how this may affect the electrical

system

describe methods of protection against overvoltage

draw the connections for surge diverters used for low voltage electrical

installations

test surge diverters used on low voltage electrical installations

explain the causes of undervoltage and how this may affect the electrical

system

describe methods of protection against undervoltage.

REFERENCES:

Electrical Wiring Practice. 6th Edition. Petherbridge K & Neeson I

Volume 2 pages 42-47.

Electrotechnology Practice. 1st Edition. Hampson J. Pages 207-214


Page 6 of 181



INTRODUCTION

Protection against excessive variations in supply voltage is essential to protect

electrical equipment and personnel. These variations in supply may be caused by

external factors such as -

high voltage switching transients

lightning

switching inductive loads

supply faults.

Equipment within an electrical installation may also cause disturbances to the supply.

VOLTAGE LEVELS

Refer to clause 1.4.98 - Voltage:

Differences of potential normally exist between conductors and between conductors

and earth as follows -

extra low voltage - not exceeding ____________ or ____________ ripple free dc

low voltage - exceeding extra low voltage, but not exceeding ________ or ________

high voltage - exceeding low voltage.

SUPPLY CHARACTERISTICS

Refer to clause 1.6.2 - Supply characteristics:

The nominal voltage and tolerances for low voltage supply systems and electrical

installations in Australia are -

_________________________________________ (in accordance with AS 60038).

Example 1:

Calculate the range of voltages available at the point of supply for a single phase

installation given the above voltages and tolerances.

___________________________________________________________________

___________________________________________________________________

Within a distribution system –

installations closer to the distribution transformer will have _________________

voltages at the point of supply

installations further from the distribution transformer will have ______________

voltages at the point of supply.


Page 7 of 181



EXCESSIVE FLUCTIONS AND/OR DISTORTIONS OF THE SUPPLY

Refer to clause 1.10.2 of the Service and Installation Rules – Limits on the

connection and operation of equipment.

The electrical distributor may refuse to permit the connection of equipment if it

considers the supply to other customers is adversely affected.


Page 8 of 181



Example: 2

Using the NSW Service and Installation Rules, provide two examples of equipment

that would cause fluctuations in the voltage and distortion of the supply wave shape:

Voltage Fluctuation: _______________________________________

_______________________________________

Wave Shape Distortion: _______________________________________

_______________________________________

UNDERVOLTAGE

Under-voltage could be considered a: complete loss of one or more phases of the supply

or brief interruption to the supply voltage.

Refer to clause 2.1.2 – Selection and installation

Switchgear and control gear shall be selected and installed to perform the following

functions or have the following features associated with the proper design, correct

construction and safe operation of the electrical installation:

Provide protection of the electrical installation against failure from

_________________________ or _______________________ conditions.

Refer to clause 2.8 – Protection against under voltage.

Suitable protective measures shall be taken where the ___________ and subsequent

_____________________ of voltage; or a _____________ in voltage; could cause

______________ to persons or property.

Example 3:

Provide an example of where restoration of voltage after a loss of supply could cause danger.

_____________________________________________________________________

_____________________________________________________________________


Page 9 of 181



KM1

4

L1

L2

L3

F2

F3

F4

TOL KM1

KM4

Start Stop

M

3

F5

F1

Refer to clause 2.8.2 – Selection of protective device

Where the re-closure of a protective device is likely to create a dangerous situation,

the re-closure shall not be _______________________________.

Example 4:

Provide two examples of under voltage protection devices:

_________________________________________

_________________________________________

Example 5:

Explain how the DOL motor starter shown in figure 1 prevents automatic re-closure of

the supply to the motor, following the loss of supply.

Figure 1

___________________________________________________________________

___________________________________________________________________

Figure 2 shows an example of a third under voltage protective device,

known as a phase failure relay. The relay operation is as follows.

Phase Failure:

When the monitored 3 phase supply voltage is valid, the output relay is

ON. Should any of the 3 phases fail, the output relay switches OFF

immediately.

Phase Sequence:

When the phase sequence is correct (R, W, B in clockwise direction).

The output relay is ON, should the phases not be in the above sequence,

the output relay will be switched OFF immediately.

Figure 2


Page 10 of 181



Figure 3 shows the motor starter circuit of figure 1 modified to include a phase failure relay.

Figure 3

______________________________________________________________________

______________________________________________________________________

______________________________________________________________________

Example 6:

For each of the items of equipment listed in table 1, identify if they would be suitable

or unsuitable for automatic re-closure of the supply.

Table 1

Equipment Automatic Re-closure

Suitable Unsuitable

Lathe in a fabrication shop

Conveyor in a mail handling centre

Air conditioning system

Refrigeration plant for a cool room

Power hacksaw

Sump pump

Fire hydrant booster pump

Lifts in a multi-storey building

KM1 4

L1

L2

L3

F1

F2

F3

F4

TOLKM1

KM4

Start Stop

M

3

PFR

1

PFR

F5


Page 11 of 181



OVERVOLTAGE

Refer to clause 2.7 – Protection against overvoltage

Where an electrical installation is protected against over voltages which may cause

danger to persons or property the requirements of clauses 2.7.2 and 2.7.3 shall

apply.

The causes of overvoltage in an electrical installation include -

________________________________________________________________

________________________________________________________________

________________________________________________________________

________________________________________________________________

________________________________________________________________

Refer to clause 2.7.2 – Protection by insulation or separation:

Measures to prevent danger due to faults between live parts of the electrical

installation and circuits supplied at higher voltages shall consist of -

conductors - the provision of adequate _______________, ________________

or _______________ of circuits in accordance with clause 3.9.8.3

transformers - the provision of adequate _______________, _______________

or _________________ of windings.

Refer to clause 2.7.3 – Protection by protective devices:

Protective devices may be used to protect against the effects of overvoltage arising

from such causes as lightning and switching operations.

Where installed such devices shall –

limit the (transient) voltage to a value below the ______________________

level of the electrical installation or the part thereof that the device protects; and

operate at voltages __________________ than or ______________ to the

highest voltage likely to occur in normal operation; and

cause no ________________ to persons or livestock during operation.

Example 7:

Is it mandatory to provide electrical installations with: overvoltage protection?

_____________________________________________________________ surge protection devices (SPDs)?

_____________________________________________________________


Page 12 of 181



Example 8:

From the items of equipment listed in table 2, identify those items that are likely to produce an overvoltage.

Table 2

Equipment

Produce Overvoltage

Yes No

Electric welder

Incandescent lamp

Electric motor started DOL

Radiant heater

Induction furnace

Hot water element

X-ray machine

SURGE PROTECTIVE DEVICES

Sudden increases (surges) in voltage can be caused by - Electricity Distributor switching operations

close lighting strikes

changes in demand caused by large energy consumers such as factories,

shopping centres and hospitals.

These high voltages are variously known as - voltage surges

overvoltage

voltage transients

voltage spikes.

Switching of electrical equipment inside the installation such as lights and motors can also cause voltage surges.

If adequate protection is not installed, voltage surges may damage sensitive electronic equipment such as – appliances – televisions, stoves, dishwashers, refrigerators, washing

machines and videos

computers

fax machines

photocopiers

printing equipment

telephone systems.


Page 13 of 181



Two forms of protection may be utilised –

lightning arrestors

surge diverters.

The lightning arrestor has two important functions – it must discharge the high

voltage surge to earth, and it must prevent leakage to earth at normal working

voltage. There are two basic types of lightning arrestor –

valve type; and

expulsion type.

Both are used extensively throughout high voltage transmission and distribution

systems, with the valve type commonly used on distributors’ and consumers’ low

voltage systems. Figure 4 shows an example of a value type arrestor and figure 5 an

expulsion type.

Figure 4 Figure 5

The operation of the valve type arrestor is as follows. When a lightning strike occurs

on the line, the high-voltage surge flashes over the series connected spark gaps and

discharges through the VDR to earth. This is the equivalent of a short circuit to earth

for the duration of the discharge. Once the surge energy has dissipated to earth, the

VDR reverts to its normal high resistance state.

The expulsion type arrestor has an adjustable spark gap. In this type, the de-

ionisation of the discharge path is achieved by the production of internal gases and

an explosive blast that expels them through the open end of the device. The use of

the expulsion arrestor is limited to rural areas.

Live conductor

Earth connection

Spark gaps

Valve element – Non-linear resistor or voltage dependent resistor (VDR)

Live conductor

Earth clamp

Mounting bracket

Expulsion tube

Fibre


Page 14 of 181



Primary Protection

Secondary Protection

Surge diverter fitted at the switchboard

Surge diverter fitted to socket outlet or plug in

power board

Surge diverters generally incorporate a Metal Oxide Varistor (MOV - which are fast

acting voltage dependent resistors), to pass voltage surges to earth via the neutral.

Surge diverters can be broken into two levels of protection basic and fine -

basic or primary protection:

against voltage surges can be provided by switchboard mounted surge diverters,

which limit peak voltages to around 2.5kV. The resistance of the MOV (metal oxide

varistor) is around 430kΩ at 430 volts RMS. However, the resistance drops to only

2.3Ω at 700 volts peak.

fine or secondary protection:

is provided by socket outlet type surge diverters that limit peak voltages to approx.

800V. Some manufacturers supply switchboard mounted secondary protection.

Figure 6 illustrates the concept of primary and secondary protection.

Figure 6

Figure 7 shows test wave forms that are used to emulate real life transients from which

surge protection devices are designed. The larger wave shows a transient a spark gap

product must endure during a lightning strike. The smaller wave shows the transient a

varistor must endure during a switching transient or an indirect lighting strike.

Figure 7


Page 15 of 181



Surge diverters are labelled using the following system –

75kA (10/350S)

75kA is the impulse current.

10/350S. The first vale (10) is the rise time of the wave (from 10% to 90% of

the peak). The second value (350) is the duration for the wave to decrease to

half its peak value.

20kA (8/20S)

20kA is the impulse current.

8 is the rise time of the wave (from 10% to 90% of the peak)

20 is the duration for the wave to decrease to half its peak value.

The internal construction of one type of surge diverter is shown in figure 8.

Figure 8

INSTALLATION OF SURGE PROTECTIVE DEVICES

Refer to clause F1.2 – Selection and installation of SPDs

Primary SPDs should be installed near the _____________ of the electrical

installation or in the ____________________________________________.

Where premises contain sensitive electronic equipment, secondary protection in the

form of plug-in surge filters or distribution board protection may be warranted. Any

such additional SPDs should be coordinated with the SPDs installed upstream, in

accordance with manufacturer’s instructions.


Page 16 of 181



Refer to clause F1.2.2 – Installation

SPDs should be -

(a) installed ____________ the main switch but prior to any RCD devices; and

NOTE: Where the main switch is an RCD refer to Paragraph F1.2.4

(b) connected at the main switchboard between ____________ and ____________.

See figure 9.

Figure 9

SPDs shall be legibly and permanently _________________________ as to their

function, in accordance with Clause 2.9.5.1.

Refer to clause F1.2.3 – Selection of SPDs

For most domestic single-phase supplies in urban environments, a surge rating of - Imax = __________ kA per phase for an __________ μs impulse and a

minimum working voltage of __________ V a.c. is suitable.

In the case of installations in exposed locations, e.g. high lightning areas, long overhead service lines, industrial and commercial premises, it may be prudent to install SPDs with a higher surge rating, typically – __________ kA per phase for an __________ μs impulse.

Consumer neutral link Earth link

SPD

Earth electrode


Page 17 of 181



Refer to clause F1.2.4 – Overcurrent protective devices

The short-circuit withstand of the SPD, together with the overcurrent protective device,

shall be not less than the ____________________________________________ at

the point of installation.

A 40 kA SPD may be protected by a _____________ HRC fuse or circuit-breaker

having a breaking capacity not less than the prospective short-circuit current at the

point of installation or by other means recommended by the manufacturer.

If an SPD is installed on the load side of an RCD, the RCD shall have a breaking

capacity of not less than _____________.

Refer to clause F1.2.5 – Connecting conductors

Conductors used to connect an SPD to both the line via the overcurrent protective

device, and to the main earthing or neutral conductor, should be not less

than____________ and as “short and direct” as possible, with “no loops”.

The total conductor length between the two points of connection, including both

active and earth/neutral, must be less than one metre, ideally ___________ to

____________, overall.

A connection to the neutral link should be as close as practicable to the MEN

connection.

Figure 10 illustrates a range of commonly available surge diverters.

Figure 10

Figure 10

Overvoltage arrester

Lightning current arrester

Lightning current arrester

High capacity 4 pole lightning current arrester & overvoltage arrester Surge protected plug

adapter and socket outlet


Page 18 of 181



SPD CONNECTION

Depending upon the requirements of the installation surge protection may be

provided by a three stage cascaded approach. The installation protection

requirements are determined on the basis of the level of risk from lightning strikes

and switching transients. The three stages are –

Stage 1 – lightning current arresters.

Incorporate spark gap arresters that work on a similar principle to a spark plug, that

is, when the energy is large enough the spark will jump the gap. These devices can

handle high currents; however they leave a relatively high residual voltage of

approximately 4kV. Not suitable for equipment protection, but reduces energy to a

manageable level. Figure 11 shows a sectioned view of a single spark gap.

Figure 11

Stage 2 – overvoltage arresters.

Used in locations that are exposed to indirect lightning strikes and switching

transients. The most common form of protection against voltage surges. These

devices provide voltage protection to less than 1 to 1.5kV.

Stage 3 – overvoltage mains filters.

Provide additional overvoltage protection to protect sensitive electronic equipment.

Used in conjunction with overvoltage arresters to provide additional filtering to slow

down the rate of rise of voltage and reduces the let through voltage to less than

800V.

In low risk areas, as shown in figure 12, voltage surges are caused by indirect lightning strikes and switching transients.

Figure 12


Page 19 of 181



Figure 13 illustrates the most basic form of protection for low risk areas. A single

overvoltage arrestor is used to provide protection for all circuits that require such

protection. In accordance with AS/NZS 3000:2007 a 32A circuit breaker is to be

used for overcurrent protection of the SPD portion of the switchboard.

Figure 13

RCD

A N L1

10A

P2

20A

Range

25A

P1

20A

L2

10A

HWS

20A 80A

M Sw

Main earth

Main neutral

Controlled load active

General supply active

RCD

A N

Earth bar Consumers neutral link

A N E

L1 L2

A N E

P1

A N E

P2

A N E

Range

A N E

HWS

A N E Outgoing final subcircuits

OVA OVA

32A


Page 20 of 181



In high risk areas, as shown in figure 14, voltage surges could be caused by direct

lightning strikes and switching transients.

Figure 14

In this type of situation a cascaded approach is utilised. Protection is provided in two

stages at the switchboard using a lightning current arrester and an overvoltage arrester.

See figure 15.

Figure 15

***********************************

Range

25A

HWS

20A 80A

M Sw

Main earth

Main neutral

Controlled load active

General supply active

Earth bar Consumers neutral link

A N E

L1 L2

A N E

P1

A N E

P2

A N E

Range

A N E

HWS

A N E Outgoing final subcircuits

P2

A N

P1

A N

L2

A N

L1

A N

OVA LCA DEC OVA

32A

NAME: Practical 7

Page 21 of 181





– REMEMBER –



Practical 7 - Over & Under Voltage

Page 22 of 181



*************NOTES*************

.

Tutorial 1 NAME:

Page 23 of 181




Please write the answer to the following questions in your own words and quote the relevant AS/NZS 3000:2007 clause number.

1. In past versions of Standards, and in trade practice devices for protection against

overvoltage have been called 'surge diverters'. What is the internationally recognised

term, and the name given to these devices in AS/NZS 3000:2007?

_____________________________________ AS/NZS 3000 reference ____________

2. For the purposes of primary protection (formerly called 'coarse or basic protection'), at

which point should a SPD be fitted in an installation?

_____________________________________ AS/NZS 3000 reference ____________

3. Is it necessary to protect a SPD against the effects of overcurrent, where the device is

fitted at a main switchboard?

_____________________________________ AS/NZS 3000 reference ____________

4. In addition to AS/NZS 3000.2007, which AS/NZS Standard provides guidance on the

installation of SPDs in MEN systems?

_____________________________________ AS/NZS 3000 reference ____________

5. Where SPDs are fitted to a switchboard, is labelling required? If so what would be a

suitable label?

_____________________________________________________________________

_____________________________________ AS/NZS 3000 reference ____________

6. Where a fuse is used to provide overcurrent protection for a 40kA SPD, what type of fuse

is required, and what current rating is recommended?

_____________________________________ AS/NZS 3000 reference ____________

7. Where a residual current device is used as a main switch, and a SPD is fitted, what is the

recommended minimum fault current interrupting capacity of the RCD?

_____________________________________ AS/NZS 3000 reference ____________

8. What is the minimum recommended size for cabling used to connect a SPD in a

switchboard?

_____________________________________ AS/NZS 3000 reference ____________

Tutorial 1 - Basic Safety, hazards & risks

Page 24 of 181



9. Where a circuit breaker is used to provide overcurrent protection for a SPD, what rating is

required for a 40kA SPD?

_____________________________________ AS/NZS 3000 reference ____________

10. What minimum working voltage is recommended for SPDs fitted to a domestic

switchboard?

_____________________________________ AS/NZS 3000 reference ____________

11. What is the maximum recommended length for cabling used to connect a SPD in a

switchboard?

_____________________________________ AS/NZS 3000 reference ____________

12. In which part of Section 8 of AS/NZS 3000:2007 does it recommend the disconnection of

SPD units when insulation resistance testing?

_____________________________________ AS/NZS 3000 reference ____________

13. Where it is impractical to disconnect a SPD during insulation testing, what is the

minimum permitted test voltage and insulation resistance?

_____________________________________ AS/NZS 3000 reference ____________

14. Under which conditions is it mandatory to provide under voltage protection?

_____________________________________________________________________

_____________________________________ AS/NZS 3000 reference ____________

15. Is under voltage protection required for machines such as guillotines, lathes, gates etc,

where an unexpected reconnection of supply would cause danger to persons or property?

_____________________________________ AS/NZS 3000 reference ____________

16. Name two devices that are identified in AS/NZS 3000:2007 as being considered suitable

for protection against under voltage.

_____________________________________________________________________

_____________________________________ AS/NZS 3000 reference ____________

17. Would it be acceptable to have automatic restarting of a refrigerator motor, when supplyreturned to normal after an under voltage problem had caused stopping of the motor?

__________________________________________________ reference not required

18. Would it be acceptable to have automatic restarting of a large fan motor, wholly enclosed

within a ventilation duct that is large enough to allow person access, when supply

returned to normal after an under voltage problem had caused stopping of the motor?

__________________________________________________ reference not required

Tutorial 1 - Basic Safety, hazards & risks

Page 25 of 181



************* NOTES *************

electrical safety principles hazards & risks

Documents