ELECTRICAL SAFETY AND

RISK ASSESSMENT

Presented By:-

Ar. MOHAMMED AZMATULLAH

&

Ar. KASHIF RAFI

Guided By:-Ar. Ali Ahmad Shah

M.Arch - Building Service, 2nd Year, FACULTY OF ARCHITECTURE & EKISTICS - JAMIA MILLIA ISLAMIA

New Delhi, INDIA

INTRODUCTION

• Hazard means any potential or actual threat to the wellbeing ofpeople, machinery or environment.

• Electrical hazard safety means taking precautions to identify andcontrol electrical hazards

Failing to take the necessary precautions can lead to:- injury or death- fire or property damage

Electric shock is the effect produced on the body and particularly on the nervous system by an electrical current passing through it. The effect depends on the current strength which itself depends on the voltage and body resistance

!!!...???

Common causes of electrocution are:

- Making contact with overhead wires

- Undertaking maintenance on live equipment

- Working with damaged electrical equipment - extension leads, plugs and sockets

- Using equipment affected by rain or water ingress

Electrical hazards exist in almost every workplace.

Voltage Rating

• There are four main types of electrical injuries:

• Electrocution (death due to electrical shock)

• Electrical Shock

• Burns

• Falls

Electric shock is the passing of electric currentthrough the body.Electrical contact can cause involuntary physicalmovements. The electrical current may

• prevent you from releasing your grip from a live conductor• throw you into contact with a higher voltage conductor• cause you to lose your balance and fall• cause severe internal and external burns• kill you.

A major cause of accidents involvingelectricity comes from the failure to identifythe hazards associated with live electricalequipment and wiring.

One is by electric shock and the other is by arc flash.

Electricity will take the path of least resistance.

Severity of the shock depends on: Path of current through the body Amount of current flowing

through the body Length of time the body is in the

circuit

Assessing electrical shock risk

The flash causes an explosive expansion of air and metal.The blast produces

• A DANGEROUS PRESSURE WAVE• A DANGEROUS SOUND WAVE• SHRAPNEL• EXTREME HEAT• EXTREME LIGHT.

These dangers can result in blast injuries, lung injuries, ruptured eardrums, shrapnel wounds, severe burns, and blindness. Arc flash injuries can also result in death.

ARC FLASH

An arc flash is a release of energy caused by an electric arc.

An arc flash happens when electric current flows through an air gap between conductors.

ARC BLAST• Arc-blasts occur from high- amperage currents arcing through the air.This can be caused by accidental contact with energized components or equipment failure.

ELECTRICITY

CONDUCTOR• Metals such as copper, silver, gold and aluminium.• Loose electrons in abundance so charge can be transferred easily

INSULATOR• Usually non-metallic such as wood, rubber, glass, etc• Contains few free electrons

ELECTRIC CURRENT

• Caused by the motion of electrons

• If channeled in a given direction, a flow of electronsoccurs.

DIRECT CURRENT

• - Always flows in one direction

• - Used to charge batteries, run some motors, operate magnetic

• lifting devices and welding equipment.

ALTERNATING CURRENT

• - More common in electrical work

• - Changes rapidly in both direction and value

• Are the most common shock-related nonfatalinjury

• Occur when you touch electrical wiring orequipment that is improperly used or maintained

EXPLOSIONExplosions occur when electricity provides a source of ignition for an explosive mixture in the atmosphere.

ELECTRICAL BURN

FIRE Electricity is one of the most common causes of fires both in the home and in the workplace. Defective or misused electrical equipment is a major cause.

********

ELECTRICAL ACCIDENTS - REASONS

1. Drilling and cutting through cables

2. Using defective tools, cables and equipment

3. Failure to de-energize circuits and follow Lockout/Tag out procedures

4. Failure to guard live parts from accidental worker contact

5. Unqualified employees working with electricity

6. Improper installation/use of temporary electrical systems and equipment

7. By-passing electrical protective devices.

8. Not using GFCI (ground fault circuit interrupters) devices

9. Missing ground prongs on extension cords

Nature and mechanism of electric shocks

• The nervous system of the human body controls all its movements, bothconscious and unconscious.

• The system carries electrical signals between the brain and the muscles,which are thus stimulated into action

• The signals are electro-chemical in nature, with LEVELS OF A FEWMILLIVOLTS, so when the human body becomes part of a much morepowerful external circuit, its normal operations are swamped by the outsidesignals.

• The current forced through the nervous system of the body by externalvoltage is electric shock.

• All the muscles affected receive much stronger signals than those theynormally get and operate very much more violently as a result.

• This causes uncontrolled movements and pain.

• Even a patient who is still conscious is usually quite unable to counter theeffects of the shock, because the signals from his brain, which try to offsetthe effects of the shock currents, are lost in the strength of the imposedsignals.

• Each disconnecting means legibly marked to indicate its purpose.• Switches and circuit breakers must be clearly labeled to indicate its circuit’s function

WORKING SPACE

• Sufficient access and working space around all electrical equipment, provided & maintained to provide ready and safe operation and maintenance.• Not used for storage

ELECTRICAL SAFETY MEASURES

DISCONNECTING MEANS AND CIRCUITS LABELLING

Circuit breaker forMotors 1,2,3, and 4

Disconnect switchFor motor number 3

Overloaded circuits can cause fires.

• Illumination provided for all working spaces

• The minimum headroom of working spaces aboutservice equipment, switchboards, panel- boards, ormotor control centers shall be 6 feet 3 inches

• Live parts of electric equipment guarded againstaccidental contact by approved cabinets or other

GUARDING LIVE PARTSforms of approved enclosures, or by any of the following means:(i) By location in a room, vault, accessible only to QUALIFIEDPERSONS(ii) By permanent, substantial partitions or screens(iii) By elevation of 8 feet or more above the floor or other workingsurface

ILLUMINATION AND HEADROOM

Entrances to rooms and other guarded locations containing exposed liveparts shall be marked with conspicuous warning signs forbiddingunqualified persons to enter

WIRING DESIGN AND PROTECTION• Proper colour codes prescribed for wiring should be used.

Sizing of Cable to make sure conductor temperature within permissiblelimit.Protection of Cable to protect from overload and short-circuit currentthrough it.Selective property of low smoke, zero halogen and fire-retardant

During any fire incidence, cable performance isalways a subject of doubt and comes underscrutiny by forensic department.

ADEQUATE WIRING SIZE• A hazard exists when a conductor is too small to safely carry the current.

• Using a portable tool with an extension cord that has a wire too small for the tool.

• Tool draws more current than cord can handle, can result in overheating, possiblefire without tripping the circuit breaker

• A cable design consists of conductor, insulation, sheath, armor etc and a few moreitems for special cables.

Defective or inadequate insulation is a hazard.

Insulation prevents conductors from contacting each other or you.

Never attempt to repair a damaged cord with tape.

W I R I N G

• Means shall be provided to disconnect allconductors in a building from the service-entrance conductors.

• The disconnecting means shall plainly indicatewhether it is in the open or closed position andshall be installed at a readily accessible locationnearest the point of entrance of the service-entrance conductors.

CIRCUIT BREAKERS

AVOID OVERLOADING• Too many devices plugged into circuit may result in wires heated to very high temperature & possible fire• Wire insulation melts may result in arcing & fire in area where overload exists

The circuit breaker is an absolutely essential device in the modern world, and one of the most important safety mechanisms.

• Circuit breakers shall clearly indicate whether they are in the open (off) or closed (on) position.

DISCONNECTING MEANS

Overloaded circuits can cause fires.

EARTHING/GROUNDING/BOUNDING• Very important for safety• Prevents conducting parts of equipment (ie. metal frames or lids),

which do not normally conduct electricity from becoming liveduring faults.

• No bonding• Person can receive an electric shock if equipment becomes faulty• All equipment bonded together• No potential (voltage) difference between live casing and handrail• If case becomes live fuse should blow

A Bonding system connects various pieces of conductive equipment together to keep them at the same potential. Static sparking cannot take place between objects that are the same potential.

Grounding is a special form of bonding in which conductive equipment is connected to an earthingelectrode or to the building grounding system in order to prevent sparking between conductive equipment and grounded structures.

Grounding is normally a secondary protective measure toprotect against electric shock.

EARTHING• In electricity supply systems, an earthing system or grounding system is circuitry which connects

parts of the electric circuit with the ground, thus defining the electric potentialof the conductors relative to the Earth's conductive surface. The choice of earthing system can affect the safety and electromagnetic compatibility of the power supply. In particular, it affects the magnitude and distribution of short circuit currents through the system, and the effects it creates on equipment and people in the proximity of the circuit. If a fault within an electrical device connects a live supply conductor to an exposed conductive surface, anyone touching it while electrically connected to the earth will complete a circuit back to the earthed supply conductor and receive an electric shock.

People use an earthing system mainly for these applications:

• To protect a structure from lightning strike, directing the lightning through the earthing system and into the ground rod rather than passing through the structure.

• Part of the safety system of mains electricity, preventing problems associated with floating ground and sky voltage.

• The most common ground plane for large monopole antenna and some other kinds of radio antenna.

• Other, less common applications of earthing systems include:• single-wire earth return.• part of a system that powers small devices from sky voltage.• one at each end of a ground dipole ELF antenna.

TYPES OF EARTHING SYSTEM

"T" — Direct connection of a point with earth (Latin: terra)"I" — No point is connected with earth (isolation), except perhaps via a high impedance.The second letter indicates the connection between earth and the electrical device being supplied:"T" — Direct connection of a point with earth"N" — Direct connection to neutral at the origin of installation, which is connected to the earthTN networksIn a TN earthing system, one of the points in thegenerator or transformer is connected with earth,usually the star point in a three-phase system.

The body of the electrical device is connected withearth via this earth connection at the transformer.The conductor that connects the exposed metallicparts of the consumer's electrical installation is calledprotective earth (PE; see also: Ground).

The conductor that connects to the star point in athree-phase system, or that carries the return current in a single-phase system, is called neutral (N). Three variants of TN systems are distinguished:

TYPES OF EARTHING SYSTEM

TN−SPE and N are separate conductors that are connected together only near the power

source. This arrangement is a current standard for most residential and industrial electric systems particularly in Europe.

TN−CA combined PEN conductor fulfils the functions of both a PE and an N conductor.

Rarely used.TN−C−SPart of the system uses a combined PEN conductor, which is at some point split up

into separate PE and N lines. The combined PEN conductor typically occurs between the substation and the entry point into the building, and separated in the service head. In the UK, this system is also known as protective multiple earthing (PME), because of the practice of connecting the combined neutral-and-earth conductor to real earth at many locations, to reduce the risk of electric shock in the event of a broken PEN conductor - with a similar system in Australia and New Zealand being designated as multiple earthed neutral (MEN).

TYPES OF EARTHING SYSTEM

TN-S: separate protectiveearth (PE) and neutral (N)conductors from transformerto consuming device, whichare not connected togetherat any point after thebuilding distribution point.

TN-C: combined PE and Nconductor all the way fromthe transformer to theconsuming device.

TN-C-S earthing system:combined PEN conductorfrom transformer to buildingdistribution point, butseparate PE and Nconductors in fixed indoorwiring and flexible powercords.

It is possible to have both TN-S and TN-C-S supplies taken from the same transformer. Forexample, the sheaths on some underground cables corrode and stop providing good earthconnections, and so homes where "bad earths" are found may be converted to TN-C-S.

COMPARISON

TT IT TN-S TN-C TN-C-S

Earth fault loop impedance

High Highest Low Low Low

RCD preferred? Yes N/A No No No

Need earth electrode at site?

Yes Yes No No No

PE conductor cost Low Low Highest Least High

Risk of broken neutral No No High Highest High

Safety Safe Less Safe Safest Least Safe Safe

Electromagnetic interference

Least Least Low High Low

Safety risksHigh loop impedance (step voltages)

Double fault, overvoltage

Broken neutral Broken neutral Broken neutral

Advantages Safe and reliableContinuity of operation, cost

Safest Cost Safety and cost

Earthing and bonding principles and prevalent practices. .

• Earthing and Bonding have often been confused as being the same thing when in fact the two are quite distinct from each other.

• A Bonding system connects various pieces of conductive equipment together to keep them at the same potential. Static sparking cannot take place between objects that are the same potential.

• Grounding is a special form of bonding in which conductive equipment is connected to an earthingelectrode or to the building grounding system in order to prevent sparking between conductive equipment and grounded structures.1

ENCLOSURE FOR DAMP OR WET LOCATION

• GFCIs are generally installed where electrical circuits may accidentally come into contact with water.

• They are most often found in kitchens, bath and laundry rooms, or even out-of-doors or in the garage where electric power tools might be used.

What is a GFCI???

• Cabinets, cutouts boxes, fittings, and panel boards shall be weatherproof.

• Switches, circuit breakers, and switchboards shall be in weather proof enclosures.

• A ground-fault circuit interrupter (GFCI) can help prevent electrocution.• If a person’s body starts to receive a shock, the GFCI senses this and cuts

off the power before he/she can get injured.

• Flexible cords and cables shall be protected from accidental damage.

• Sharp corners and projections shall be avoided.

• Where passing through doorways or other pinch points, flexible cords and cables shall beprovided with protection to avoid damage.

When conductor enters a box or cabinet, they must beprotected by some type of lock or rubber perforationfrom the sharp edges of cabinets, boxes, or fittings• All pull boxes, junction boxes and fittings must beprovided with approved covers• If covers are metal they must be grounded.

BOXES & CABINETS

TEMPORARY WIRING

• Safety signs, safety symbols, or accident prevention tags shallbe used where necessary to warn employees about electricalhazards

• Barricades shall be used in conjunction with safety signs

• If signs and barricades do not provide sufficient warning andprotection from electrical hazards, an attendant shall bestationed to warn and protect employees

The following alerting techniques shall be used to warn and protectliving being from hazards which could cause injury due to electricshock, burns, or failure of electric equipment parts:

FUSES AND RCD’sFUSES• Will cut off supply at a certain current level

• i.e. 13A, 5A, 3A mains supply fuse.

• Fuse has a ‘fusible’ wire element which heats

up when current flows.

• Excessive current = excessive heat & wire

• melts preventing current flow

RCD’s

• Residual current device

• Compares current in Live & Neutral,

• if different and above a certain value supply switched off

FUSEHRC FUSESMCBMCCBRCDELCBOIL CIRCUIT BREAKERGAS CIRCUIT BREAKERVACCUM CIRCUIT BREAKERRELAYS….

A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused byoverload or short circuit.

What is safety device of diesel generator?

• safety devices of generator depends on the type of prime moverused in generator.

• The main safety devices in a DG Set is to control the over speed, tolimit the fuel supply in case of emergency.

• It is regulated by the governor of the DG Sets. In external safety, overvoltage & over current tripping relay i.e. associated with DG Setscontrol panel.

• Some small control transformers have a built in primary fuse.• Larger transformers are primary fused externally and pole

transformers are primary fused externally with the fuse holdersmounted on cross arms near the transformer.

StandardsRating of Outlets:-To be adopted for design:1. Incandescent lamps in residential and non-residential buildings shall be rated at 60W and

100W respectively.2. Ceiling fans shall be rated at 60W. Exhaust fans , fluorescent tubes, compact fluorescent

tubes, HPMV lamps, HSPV lamps etc, shall be rated according to their capacity. Control gear loses shall be also considered as applicable.

3. 6A and 16A socket outlet points shall be rated at 100W and 1000W respectively, unless the actual values of load are specified.

Capacity of circuits:1. Lighting circuit shall feed light / fan. Call bell points. Each circuit shall not have more than

800W connected load or more than 10 points. 2. However, incase of CFL points where load per point may be less number of points may be

suitably increased.2. Power circuit in non residential building will have only one outlet per circuit.3. Each power circuit in residential building can feed following outlets :a)Not more than 2 nos. 16A outletb)Not more thane 3nos. 6Ac) Not more than 1 No. 16A and 2 Nos. 6A outlets.4. Load more than 1KW shall be controlled by suitably rated MCB and cable size shall be decided as per calculation

copper conductor cable only will be used for sub main/circuit/point, wiring.Minimum size of wiring light Wiring: 1.5 Sq.mm.Power Wiring: 4.0 Sq.mm.Power circuit rated more than 1KW , size as per calculation.Insulation:copper conductor cable shall be PVC insulated, Fire retardant , low smoke (FRLS) type conforming to BIS specification.Multi Stranded : Cables are permitted to be used.

Standards

Cables:

light Wiring: 1.5 Sq.mm. Unfortunately, there is no straightforward answer to this question. A cable's current-carrying capacity depends on various factors, including: the number of cores, its type of insulation, whether it's armoured or not, and the method of installation. Depending on these factors, the current-carrying capacity varies from around 14 A to around 21 A, but for specific information, you'll need to check out the appropriate Tables in BS7671:2008 Requirements for Electrical Installations.

How calculate current carrying capacity of 16 sq mm copper wire?

• AS PER THUMB RULE THE CURRENT CARRYING CAPACITY OF WIRE IS 4 TIMES OF ITS CROSSECTIONAL AREA OF WIRE i.e. 10 sq.mm wire carrying maximum current 40 amp , 16 sq.mm carrying maximum current 64 amp ,

• now amp convert in watt by multiplying by volt i.e. 240

• 16 sq.mm carrying max load 64x240= 15360 watt

Rules • Indian Electricity Rules, 2005 defines the basic fundamentals of Electricity Safety, and when

followed in totality there cannot be any incidence of electrocution or electric fire.

• General Safety requirements are given in Chapter IV under rules 29 to 46 which covers installation, protection, operation, maintenance cut-out, identification of earth, earthed terminal, danger notice etc.

• General Rule 29 covers installation shall be constructed, installed, protected, worked and maintained in accordance with BIS. It further stipulates that the material and equipment used shall conform to the relevant specifications of the BIS.

• The National Electrical Code issued by BIS states in Clause 3.1.3.6 that the current rating of a fuse shall not exceed the current rating of the smallest cable in the circuit protected by the fuse.

• Rule no 31 talks about protection of every line by a cut-out. A cut out is defined as any appliance for automatically interrupting the transmission of energy through any conductor when the current rises above the pre-determined amount and shall also include a fusible cutout.

• Rule 45 speaks that only authorized person shall be permitted to carry out electricity work who is licensed by the the Government.

• Rule No. 32 and 33 speaks about earthed terminal for the purpose that if the current leaks out, it should not harm the being but get discharged to earth immediately.

Do’s and Don’ts for Electrical Safety – Home and general public – 230V and HT supply

• 230V AC is house hold supply and can be dangerous.

• Ensure three pin plug socket, earth connection on appliance and wire continuity and its resistance.

• Earth pin is thick for its ability to carry high fault current and long for it to touch first before phase is connected.

• Ensure socket closure mechanism to prevent children entering their finger inside

• Earth leakage current if not flowing through earth wire will find path through damp wall and pipe line and may be fatal.

• Provide earth leakage detector(RCB) along with over current protection (MCB)

• Be watch full if duty cycle of any socket is very high. There is possibility of loose connection which may result overheating, smoke and even fire.

• Check LT over head line is protected by a guard wire

• Ensure HT supply in your area is properly fenced and impossible for children to find entry

Worker end• Use safety and testing tools – Rubber sole shoes, Helmet,

safety sling (working on HT line), Continuity tester,

• Switch off power supply, test personally and fix sticker ‘Menat Work’

• Take permit to work when working on HT line

• Never keep any inflammable item near electrical installation

• Protect HT switching station from rodent/lizards etc.

• Ensure provision of danger board

• Fence the HT area from unauthorized entry of even animals.

• Never assume and always test to be certain

Area required for generator in electrical substation

• A good example is the 'no-let-go' effect. Here, a person touches a conductor which sends shock currents through his hand. The muscles respond by closing the fingers on the conductor, so it is tightly grasped. The person wants to release the conductor, which is causing pain, but the electrical signals from his brain are swamped by the shock current and he is unable to let go of the offending conductor.

• The effects of an electric shock vary considerably depending on the current imposed on the nervous system, and the path taken through the body. The subject is very complex but it has become clear that the damage done to the human body depends on two factors:

• 1. - the value of shock current flowing, and2. - the time for which it flows.

References

• tlc-direct.co.uk/Book• NBC• IEEE• BIS• Electrical Safety Hand book• Electrical Hazard General

Thanks