2391- inspection & testing (basic)

7/27/2019 2391- Inspection & Testing (Basic)

1/118

1

www.ElectaCourse.com

Inspection Testingnspection Testing

Basic)

Basic)

ElectaCourse.com

2005 Last Updated August 2006


2/118

2


A problem with many

installations, particularlydomestic, is that

Every man and his dog has had a

hand in it


3/118

3


periodic inspection and testing to ensurecontinued safety is unlikely

additions/alterations possibly undertakenby unqualified persons

The domestic electrical installation

likely to have been originally installed

by competent electrical contractor


4/118

4


To what standards should anelectrical installation conform?

The Institution of ElectricalEngineers Wiring Regulations


5/118

5


First Edition of the Regulations

Issued in 1882 and entitled

Rules and Regulations for thePrevention of Fire Risks

Arising from Electric Lighting


6/118

6


What about risk of electric shock

and death by electrocution?


7/118

7


Jointly owned by the Institution of

Electrical Engineers and B.S.I.

Latest edition

1st January 2002

Came into effect

BS 7671:2001


8/118

8


Are these regulations statutory?

No, but they can be used as

evidence of compliance with

statutory regulations

limited value within the domestic

installation in terms of enforcement


9/118

9


Very few enforceable regulations

apply to domestic installations


10/118

10


The commercial or industrial electrical

installation usually under the controlof competent persons.

Statutory measures in place toensure a safe working environment.

This includes the electrical

installation and electrical equipment


11/118

11


Failure to comply with statutory regulations

within the workplace can lead to criminal

prosecution


12/118

12


Other Interested Parties


13/118

13


Two organisations concerned with the

quality and safety of all aspects of electrical

installation work in including domestic


14/118

14


The Electrical Contractors Association

E.C.A.

National Inspection Council for Electrical

Installation Contracting

N.I.C.E.I.C.


15/118

15


Organisations only concerned with the

competence and quality of work for

those electrical contractors whoare members of their organisation


16/118

16


What happens if an electrical contractor

carries out work in an unsatisfactorymanner?

If the contractors are members of the ECA

or NICEIC, then appropriate action can be

taken

If not, the trading standards office, or localauthority may be able to help


17/118

17


With many domestic installations there is

little or no maintenance undertaken toensure continued safety

In many cases, the integrity and safety ofthe installation is reduced by the D.I.Y.

person!


18/118

18


The need for Inspection and Test


19/118

19


Installations should be inspected and tested

before being put into service -

(initial verification)

at regular intervals thereafter -

(periodic)

on completion of any alterations or

additions


20/118

20


The Initial Verification


21/118

21


For an initial verification

BS 7671:2001states:

installed equipment to an appropriate

standard, i.e. BS, BS EN etc.

correctly selected and erected

not visibly damaged or defective as toimpair safety


22/118

22


The periodic installation inspection

BS 7671:2001states

Periodic inspection and testing of an

electrical installation shall be carried out todetermine,so far as is reasonably

practicable, whether the installation is in a

satisfactory condition for continued service


23/118

23


Generally, the main reason for undertaking

an inspection and test is to ensure that the

installation is safe to use


24/118

24


What are the likely reasons for an

installation failing to be safe?

Age

Wear and tear - may be considerable inrented accommodation

Botched work by incompetent persons, or

unscrupulous contractors


25/118

25


Periodic Inspection Report

Where is it required?

expiry of current certificate

change of ownership or use

as a result of damage - flood, fire, etc

mortgage/insurance purposes


26/118

26


Factors affecting the safety

some common factors will include:-


27/118

27


Damage to equipment or accessories

Poorly installed equipment/accessoriesLoose connections giving rise to shock/fire

Overloaded circuits

Inadequate protection of circuits againstovercurrent

Circuit cables inadequate to safely carry

load currentInadequate earthing arrangements


28/118

28


The visual InspectionThe visual Inspection


29/118

29


For reasons of safety the supply

should preferably be switched off

prior to conducting the inspection


30/118

30


Checking fixings of accessoriesChecking fixings of accessories

and cablingand cabling


31/118

31


Loose connections may result in

e l e c t r i c s h o c k e l e c t r i c s h o c k

f i r e f i r e


32/118

32


circuit connections may be dislodged by

movement of the socket outlet .

terminations should be checked before

socket is secured

remember, loose

connections may

give rise to fire

and shock


33/118

33



34/118

34



35/118

35


circuit connections may be dislodged by

movement of the joint-box .


36/118

36


Thats assuming they bothered to use

a joint box in the first place.


37/118

37


Blimey hes even left

the screwdriver bit

in the terminal block

potential fire/shock risk due to mechanical

damage or loose connections


38/118

38



39/118

39


Overheating due to loose connectionsOverheating due to loose connections


40/118

40



41/118

41


Correct connection of single-way switch

surface box

secure

earth wire

sleeved

terminations secure


42/118

42


Basic one-way lighting circuit

switch

Lamp

P

N


43/118

43


switch

lamp

P

N


44/118

44


Switch connections

for two-way lighting


45/118

45


P

N


46/118

46


P

N


47/118

47


P

N


48/118

48


P

N

El t C


49/118

49


P

N

El t C


50/118

50


When converting one-way

to two-way lighting the earth

wire used as live conductor

Very dangerous practiceVery dangerous practice

El t C


51/118

51


When installing socket outlets

www ElectaCourse com


52/118

52


accessory secure

correct amountof sheath

terminations

secure

appropriate

standard BS1363

correct cable size



53/118

53


Fuses and Circuit Breakers



54/118

54


The purpose of a fuse or circuit breaker

device is automatically to interrupt circuit

current in the event of fault or overload

conditions



55/118

55


Excessive current may flow as a result of:

overload (excessive connected load)

short circuit between live and neutral

earth fault (live or neutral to earth)



56/118

56


Overload

(excessive connected load)



57/118

57


Under normal circumstances

the fuse or circuit breaker

should operate before the

circuit cables reach adangerously high

temperature



58/118

58


If the fuse or circuit breaker is to high for

the circuit, the cables may reach a dangerously

high temperature resulting in fire



59/118

59



Sh t i it


60/118

60


Short circuit

Phase and neutral conductors touching

Phase to neutral short resulting from

loose connections at a socket outlet

Large fault current flows - fuse or circuit

breaker should operate



61/118

61

Result of electrician fitting circuit breakerto live board



62/118

62



63/118

63

Least sensitive of the two devices and protectscircuits feeding fixed equipment.

Combined main switch and r.c.d.


E th f lt


64/118

64

Earth faulta fault condition that exists between live

conductors and earth

Excess current should cause fuse or

circuit breaker to operate



65/118

65

rewirable fuse -

most widely abused



66/118

66

Incorrect size of element

Most likely reason fordevice failing to operate



67/118

67

fuse element too large



68/118

68

a fuse failing to operate under

fault conditions may well

result in fire



69/118

69

The Rewirable fuse is an antiquated

device. even with the correct

rating of fuse element it may not safelyinterrupt high levels of fault current



70/118

70

Cartridge fuses to BS 1361

scattering of hot metal particles

contained within cartridge thusreducing fire risk during

operation

operates much closer to itscurrent rating when compared to

the rewirable fuse



71/118

71

has the ability to interrupt high levels of fault

current less likelihood of premature failure due to

oxidisation when compared to the rewirable



72/118

72



73/118

73

Selection of fuses used in consumer units



74/118

74



75/118

75

Circuit-breakers to BS EN 60898

most widely used type ofovercurrent protective device,

particularly for domestic applications

Thermal-magnetic operation

thermal - overload

magnetic - short circuit conditions

Older miniature circuit breakers toBS 3871




76/118

76


rating (A) application

6 lighting circuits

20 13A socket radial

32 13A socket rings

32 13A socket radial

45 cooker/shower circuits

3 bell transformers

16 immersion heaters



77/118

77

The Residual Current Device (r.c.d.)

Provides protection against earth faults interms of:

electric shock, and

fire of an electric origin



78/118

78

Why bother with an r.c.d. when a fuse or circuit

breaker can provide protection against earth fault

conditions?



79/118

79

an r.c.d can operate in the region of milli-amps

in fact a r.c.d. rated at 30mA can provideprotection against electrocution



80/118

80

fuses and circuit breakers require relatively

high currents in order to operate

for example, for a 30A rewirable fuse requires

approximately 200A to operate within a safe

time period



81/118

81

Types of r.c.d.



82/118

82

Socket outlet incorporating r.c.d. protection

High level of personal

protection against shock,

particularly when using

portable electrical

equipment outdoors


D ti it ith t d


83/118

83

Domestic consumer unit with two r.c.d.s

Extensively used in conjunction with an earthelectrode earthing system



84/118

84

Second r.c.d. has greater sensitivity and isused to protect socket outlet circuits

Providing personal protection


Combined r.c.d. circuit breaker (RCBO)


85/118

85

single device providesprotection against both

overload, short circuit and

earth fault currents





86/118

86


An r.c.d. is a device which can provide protection

against:

fire resulting from earth faults

earth faults where circuit resistance is too high

for protection by conventional devices, i.e.

circuit breakers or fuses

where greater protection against electric shock,

for example socket outlet circuits likely tosupply portable equipment outdoors



87/118

87

fuses and circuit breakers are totally unable to

provide this level of shock protection



88/118

88



89/118

89

What rating of r.c.d. are generally available and

where would they be used?

as a guide



90/118

90

30mA for personal protectionsocket outlet circuits

100mA or above for protectionagainst fire



91/118

91

verification of polarity

most importantly, at socketoutlets



92/118

92

correct polarity

is essential


socket outlet correctly wired


93/118

93

the earth pin of the socket

connects directly to the

exposed metalwork of the

appliance

socket outlet correctly wired

P

N

E



94/118

94

What happens

when the phase

and earth

connections arereversed?

incorrect polarity can lead to death by

electrocution


The phase and c.p.c. reversed


95/118

95

the phase conductor is

directly connected to the

exposed metalwork of the

appliance

p

From

supply


Correct polarity


96/118

96

Edison-screw

Correct polarity

Correct polarity of Edison-type screwfittings essential if shock is to be avoided


97/118



98/118

98

neutral

phase



99/118

99

Phase

Neutral

Phase and neutral connections reversed



100/118

100

A person removing an Edison-screw lamp

could receive a serious electric shock if

they touched the lamp thread before it

had completely been removed from thefitting

Reversed polarity



101/118

101

Verification of polarity can be quite

a complex affair and generally only

undertaken by competent persons



102/118

102

However! If commonsense is applied

rudimentary testing may be undertaken

at socket outlets by using a socket tester


The socket tester


103/118

103useful but limited in its application

e soc e es e



104/118

104All lights green indicates correct polarity


105/118


106/118


Th k t t t ill INDICATE


107/118

107

The socket tester will INDICATE

THE PRESENCE OF SUPPLY

IDNETIFY THE CORRECT POLARITY OF THE

PHASE CONDUCTOR

THAT SOME FORM OF EARTH CONNECTION IS

PRESENT AT THE SOCKET OUTLET


The socket tester ill NOT INDICATE


108/118

108

The socket tester will NOT INDICATE

A HIGH RESISTANCE EARTH PATH

A REVERSED NEUTRAL

EARTH CONNECTION


AND ABOVE ALL


109/118

109

NEVER USE A SOCKET TESTER TO PROVE

THAT A CIRCUIT IS ISOLATED, (dead).

AND ABOVE ALL


Earthing


110/118

110

Earthing

In order to prevent electric shock the exposedmetalwork of electrical appliances, metal

conduit etc should be earthed.

In the majority of cases the earthing facility is

provided by the local electricity supplier.



111/118

111

Inadequate earthing arrangements may lead

to electric shock or death through electrocution



112/118

112

Earthing arrangements


Typical domestic intake


113/118

113main incoming earth

earth

terminal

consumer unitmeter

service cutout


Earth connection is obtained from suppliers


114/118

114

sheath (main incoming cable)

This method of earthing is still widely used

and is reliable


Modern earthing arrangement where the earth


115/118

115

g g

is connected to the incoming neutral at the

service head

Rapidly becoming the most widely used

supply arrangement


116/118



117/118

117

Earth rod and typical enclosure


Problems with earth electrodes


118/118

Problems with earth electrodes

generally does not provide a very good

earth return path

liable to corrosion and mechanical

damage

2391- inspection & testing (basic)

Documents