Safety In Safety In ElectricityElectricity

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ElectricityElectricity

PREPARED BY:-AADARSH

CHANDRAPRAKASH

Primary HazardsPrimary Hazards

�Electric shock

�Electric fire & explosion

�Electric flash

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�Electric flash

�Electric burns

Electric ShockElectric Shock

� It is sudden & accidental stimulation of the

body’s nervous system by electric current. It

is the result of passage of electric current

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is the result of passage of electric current

through the human body

Severity of Shock Depends Severity of Shock Depends --

�Duration of flow

�Amount of current

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�Path of flow of current

�Type of energy

Body ResistanceBody Resistance

BODY PART RESISTANCE(ohms)

Dry skin 1,00,000-6,00,000

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Wet skin 1000

Hand to Foot 400-600

Ear to Ear 100(approx.)

• I = V / R

POWER

SOURCE

Person

in touch

with

live wire

P

N

6

• I = V / R

= 230 / 100000 A (Dry Condition)

= 0.0023 A

= 2.3 mA

• I = 230 / 5000 (Wet Condition)

= 0.046 A

= 46 mA

Effect of Electric Current on Human BodyEffect of Electric Current on Human Body

EFFECT ON HUMAN –50Hz

Shock, Let – go border line of painful shock, Muscles still under control

<= 10 mA >= 10 mA

Muscle control affected 15 mA

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Muscle control affected 15 mA

Breathing difficulties start 20 mA

Severe shock & possible death due to rapid, uncoordinated series of contraction of heart muscles causing irregular heart beat & possible death

50 mA > 3 sec.

How Shock OccursHow Shock Occurs�By simultaneously touching the phase and

neutral conductor thus completing the

circuit through his body

Y

ALTERNATOR

8

R

B

N

LOAD HAVING

METALLIC BODY

2. By touching the phase conductor and

standing on the ground

ELEC. EQPT.HAVING

ALTERNATOR

Y

B

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N

ELEC. EQPT.HAVING

METALLIC BODY

R

3. By touching a metallic part that has become

live by itself being in contact with an

energised wire

ELEC. EQPT.HAVING

ALTERNATOR

Y

B

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N

ELEC. EQPT.HAVING

METALLIC BODY

R

Shock Protection MethodsShock Protection Methods

� Isolation

�Current limitation

�Low voltage

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�Low voltage

�Double insulation

�Earthing

IsolationIsolation

��All electrical equipment should be isolated All electrical equipment should be isolated

from accidental contact & approach by from accidental contact & approach by

unauthorised men. Providing barrier unauthorised men. Providing barrier

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unauthorised men. Providing barrier unauthorised men. Providing barrier

��Panel boards, generators, large motors, Panel boards, generators, large motors,

batteries should be enclosedbatteries should be enclosed

��Low & medium voltage OH lines should be Low & medium voltage OH lines should be

kept 19’ above the groundkept 19’ above the ground

Isolation SwitchesIsolation Switches� The switches should be connected in phase only

� The switches should be easy and free to operate

� Body of the metallic switches should be earthed

� Every DB should be provided with a switch

� It is advisable to keep switch as near as possible to the

work-place

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P

N

POWER

SOURCE

� If switch is connected in neutral, the person, who repairs

the equipment, could get shock though the supply is cut

using the switch.

Isolation TransformerIsolation Transformer

� Power can be tapped from isolation transformer

� Avoids shock between earth and phase

SINGLE PHASE

TRANSFORMER

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Low VoltageLow Voltage

�24V hand lamps.

�By earthing the mid point of a single phase transformer, the

line to earth voltages are reduced to 115V while the full

supply(230) is available to the apparatus.

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CENTRE TAPPED

TRANSFORMER

230V

115V

Double InsulationDouble Insulation

•Another insulation added.

•Double insulated power tools have non-metallic

body

•Need not be earthed (two point plug is sufficient)

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•Need not be earthed (two point plug is sufficient)

InsulationInsulation

Functional Functional Protective Protective

Electrical SafetyElectrical Safety

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Electrical SafetyElectrical Safety

Site requirements

Check in General forCheck in General for

�Neutral earthing (In case of X-mer or DG)

�Protective shed

�Body earthing

�Earth pit for body earthing

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�Earth pit for body earthing

�Earth resistance

�Fuses

�Loose connection of cable

�Housekeeping

�Fire extinguisher and type

ELCB

Sub Distribution Board

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ELCB

63 A

30 mA

PLUG TOPS

• Plug tops should be used to avoid shock danger.

• Three point plug in case of metallic body handtools and two point plug in case of doubleinsulated hand tools.

20HAND TOOL

METALLIC BODY

EarthingEarthing

NEUTRAL EARTHINGNEUTRAL EARTHING EQUIPMENT EARTHINGEQUIPMENT EARTHING

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NEUTRAL EARTHINGNEUTRAL EARTHING EQUIPMENT EARTHINGEQUIPMENT EARTHING

Earthing Scheme for Construction Power Earthing Scheme for Construction Power

FacilitiesFacilities

MAIN DB

EARTH ELECTRODE

50 X 6 G.I. FLAT

CLIENTS

INTERCONNECTION WITH

EARTH ELECTRODEDRG NO. STD/GRD/021

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MAIN DB

SUB - DBPIPE EARTH PIPE EARTH

DRG NO. STD/CONP/002

FDBPIPE EARTH PIPE EARTH

EARTH CONTINUITY CONDUCTOR(SEPARATE OR AS THIRD / FOURTH CORE

25 X 3 G.I. FLAT

NO. 8 SWG G.I. WIRE

INTERCONNECTION WITHCLIENTS EARTH GRID

Details of Earthing Station With GI PipeDetails of Earthing Station With GI Pipe

STRIP

20

0

EARTH LEADEARTH LEAD

4” φGROUND LEVEL

BRICK IN LIME

OR CEMENT

FUNNEL229338229

305

RCC SLAB (WITH IDENTIFICATION

MARKING)

CHARCOAL OR COKE IN

DR

G N

O.

ST

D/G

RD

/02

4

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x x

SECTION ‘X’ - ‘X’

12 φ HOLE

CHARCOAL OR COKE IN

POWDER FORM MIXED

WITH SALT & CLAY38 NB

GI PIPE

2700mm LONG

2500 (MIN.)

150 150

NOTE: SUFFICIENT WATER TO BE

POURED INTO SUMP TO KEEP

SOIL SURROUNDING EARTH PIPE

PERMANENTALY MOIST

DR

G N

O.

ST

D/G

RD

/02

4

TRANSFORMER NEUTRAL EARTHING TRANSFORMER NEUTRAL EARTHING -- SIZE OF SIZE OF

EARTH LEADEARTH LEADTRANSFORMER RATING

ELECTROLYTIC BAREE COPPER CONDUCTOR OR STRIP

INSULATED (PVC) SINGLE CORE STRANDED ALUMINIUM

G. I. CONDUCTOR OR STRIP

50 KVA AND BELOW

8 SWG 16 SQMM 1” * 1/8” (25 mm * 3 mm)

75 KVA 8 SWG 25 SQMM 11/2” * ¼” (40 mm * 6 mm)

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mm * 6 mm)

100 KVA 4 SWG 35 SQMM “

150 KVA 2 SWG OR 1” * 1/16”

70 SQMM “

200 KVA 1” * 1/16” 95 SQMM “

250 KVA “ 150 SQMM “

300 KVA “ 225 SQMM “

500 KVA 1“ * ¼” 300 SQMM 2” * ¼” (50 mm * 6 mm)

750 KVA 11/2” * 1/4 2*225 SQMM OR 1*500 SQMM

ABOVE 500 KVA ONLY Cu OR Al TO BE USED

EQUIPMENT EARTHING EQUIPMENT EARTHING -- SIZE OF EARTH LEADSIZE OF EARTH LEAD

(Transformers, Motors, generators, Switch gears (Transformers, Motors, generators, Switch gears

etc.)etc.)

Size of Earthing Conductor Rating of 400 V 3 phase

50 cycles equipments in

KVA Bare copper Aluminium PVC

insulated

Galvanised

Iron

UPTO 5 (4 KW) 14 SWG 6 SQMM 7/22

6 TO 15 (4.8 TO 12 KW) 10 SWG 16 SQMM 8 SWG

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16 TO 50 (13 TO 40 KW) 10 SWG 16 SQMM 1” * 1/16”

51 TO 75 (41 TO 60 KW) 8 SWG 25 SQMM 1” * 1/16”

76 TO 100 (61 TO 80 KW) 6 SWG 35 SQMM 1” * 1/8”

101 TO 125 (81 TO 100 KW) 4 SWG 50 SQMM 1” * ¼”

126 TO 150 (80 TO 100 KW) 2 SWG OR 1” *

1/16”

70 SQMM 1” * ¼”

151 TO 200 (121 TO 160

KW)

1” * 1/16” 70 SQMM 11/2” * ¼”

201 & ABOVE (161 KW &

ABOVE)

1” * 1/8” 185 SQMM 2” * ¼”

Fuses Fuses

�Fuses are proven safety devices for overload conditions

�Check the fuses for their current ratings

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�Never replace fuse wire with ordinary copper or aluminium wire

�High rupturable cartridge (HRC) fuses are now a days easily available and has advantages over traditional fuses

T

EQUIPMENT

ELCB WORKING PRINCIPLEELCB WORKING PRINCIPLENo fault Condition I1 = I2

Fault Condition I1 > I2 (I1 = I2 + IP)

Tripping Condition IP > 30 mA

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N

L

CORE BALANCE

CURRENT

TRANSFORMER

I2

I1

Ip

ELCB (EARTH LEAKAGE CIRCUIT BREAKER)ELCB (EARTH LEAKAGE CIRCUIT BREAKER)

�� For portable power tools power supply is taken through For portable power tools power supply is taken through

ELCBELCB

�� Saves persons from electric shockSaves persons from electric shock

SWITCH POWER

Person in

touch with

faulty eqpt.

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�� It opens the circuit when it senses leakage current from It opens the circuit when it senses leakage current from

earth.earth.

ELCBSWITCH

BOX

POWER

SUPPLY

faulty eqpt.

Having

elec.

Charges on

it”s body

EARTH LEAKAGE CIRCUIT EARTH LEAKAGE CIRCUIT

BREAKERBREAKER

�� For portable power tools power supply should For portable power tools power supply should

be taken through ELCBbe taken through ELCB

�� ELCB’s OF 30 mA sensitivity , 63Amps, 3 ELCB’s OF 30 mA sensitivity , 63Amps, 3

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�� ELCB’s OF 30 mA sensitivity , 63Amps, 3 ELCB’s OF 30 mA sensitivity , 63Amps, 3

polespoles

�� Test the ELCB weekly and record it.Test the ELCB weekly and record it.

Causes of Electric fireCauses of Electric fire

� Selection of improper/substandard equipment and

materials.

� Electrical installation not in accordance with statutory

regulations.

� Overloading of equipment.

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� Overloading of equipment.

� Maintenance negligence.

� Failure of insulation level.

� Damage due to rodents, termites and pests.

� Lightning.

� Water seepage.

� Static electricity.

Failure of insulation levelFailure of insulation level

Insulation failure occur due to following various reasons:-

i) Reduction in voltage with standing capacity because of

excess temperature.

ii) Deterioration in mechanical properties due to excess

temperature where the insulation is mechanically

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temperature where the insulation is mechanically

vulnerable and the mechanical failure leading to electrical

failure of the insulation.

iii) Aging causes deterioration of the insulation.

iv) Sub-standard material are more prone to insulation

failure.

Electric BurnsElectric Burns

� Chief causes are pushing of fuses inside switches,

explosion due to short circuit inside switches,

1. BURNS FROM ELECTRIC FLASH & 1. BURNS FROM ELECTRIC FLASH &

2. BURNS FROM ELECTRIC HEAT2. BURNS FROM ELECTRIC HEAT

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pressing of cables of portable machines & damage

to hand lamp cables

� Devices have been provided to protect injuries due

to above causes. High rupturable capacity fuses

are enclosed type. Covers are sealed and

mechanically interlocked

Electric FlashElectric Flash

� It is the result of the breaking of circuit of electric current

� Higher the current, slower the rate of separation of parts,

the greater is the flash

� It is the result of arcing

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It is the result of arcing

� Being a known hazard sufficient preventive measures are

taken to guard against it like magnetic blow out coil & arc

chutes

� Electric flash generally affect the eyes, if a person sees it

with his naked eyes. Personal protective equipment has to

be used

Cable RoutingCable Routing

��All electrical cables should be run either All electrical cables should be run either

overhead (7 feet) or undergroundoverhead (7 feet) or underground

��Cable routing layout map to be prepared so Cable routing layout map to be prepared so

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��Cable routing layout map to be prepared so Cable routing layout map to be prepared so

that it does not cause tripping hazardsthat it does not cause tripping hazards

��Welding and power cables not to be Welding and power cables not to be

overlappedoverlapped

Cables Cables

�Single phase supply

�Phase - red

�Neutral - black

�Earth - green

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Earth - green

�Three phase supply

�Phases

�Red

�Yellow

�Blue

�Neutral - black

PROTECTING CABLES FROM

DAMAGES

• Protection against mechanical damages

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• Protection against heat

• Cables should be laid away from welding

cables

Cable JointsCable Joints� Staggered joints

CABLE 1

3/4” 3/4” 3/4” 3/4”

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�Joints are not to be overlapped

�One primary insulation and an overall

secondary insulation is to be done

�Proper insulation tape are to be used

� Jointing kit

CABLE 2

Hand LampsHand Lamps

�Only 24V hand lamps are to be used

�Hand lamps are to be enclosed by glass

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�Hand lamps are to be enclosed by glass

surrounded by metal wire mesh

�Hand lamps used for confined space work

should be of all insulated type with no joints

Manpower Manpower

�Employ qualified electrician, preferably ‘B’

license holders

Identification of the electrician - red helmet

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� Identification of the electrician - red helmet

Registers & ProceduresRegisters & Procedures

�Weekly ELCB check register

�Lockout / Tagout

�Permit system

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�Permit system

ELCB Test Register Elec Chk List Elec Saf Report

Electrical SafetyElectrical Safety

�Employ qualified electrician, preferably ‘B’

license holders

�Display electrical equipment & cable

routing layout

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routing layout

�All electrical installation to be tested &

commissioned as per BIS codes and IER

�All DB’s should be covered

�Earthing of all electrical installations

�Regular maintenance

�Records to be maintained, ELCB

�Display caution boards

�Provide ELCB for portable

equipment

�24 V hand lamp

ELECTRICAL SAFETYELECTRICAL SAFETY

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�24 V hand lamp

�Follow rules and regulations

�Follow safety measures

�Adopt protective system

� Insulation

�Regular inspection

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WELDING RETURN CURRENT OF HIGH

VALUE THROUGH THE EARTH CABLE

Results in :

Considerable heating of the cable,

Melting of the Insulation.

Short Circuit / flash / fire.

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Path of return welding current passing

through the earth cable of the machine

I>200 amps

D.B.

A PRAGMATIC APPROACH

1> TAKE NO CHANCE - Ensure that- All covers on installations, DBs, Panels etc. are in place.

- All cable entry/ exit boxes are maintained.

- Cable glands are used and maintained.

- Cable joints are done using standard joint-kits.

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- Cable joints are done using standard joint-kits.

- Proper routing / laying of cable is done.

- Enclosure of transformers, FDBs, substations are maintained to

prevent trespassing.

- Practices like neutral earthing, center tapping of transformer are

in place and all hand lamps are connected with 24v supply.

- Earth leads of machines, switch gears, transformers are ok.

- Electricians with relevant certificate / work experience are only

deployed.

- No unauthorized entry to Electrical rooms / booths and only

authorized persons (qualified electricians) are allowed to work.

- Electricians and other personnel are trained in Electrical Safety

from time to time.

2> PEOPLE AT WORK

3> SYSTEMS

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- Work permit systems for Work on Systems, overhead transmission

lines etc.

- Work on or in the vicinity of Electrical Installations / cables will be

allowed only after taking Shut down using relevant work permit

forms.

- Lock out / Tag out systems will be adopted during electrical works.

- Neutral earthing & center tapping of transformers is done.

3> SYSTEMS

- All equipment, machines, switch-gears are periodically taken for

maintenance and a record is kept.

- Insulation resistance are tested for cables, motor windings etc with

the help of megger.

- Earth resistance is checked. Earth pits are maintained properly.

(Use charcoal & salt to the earth pits to keep the resistance low.)

- Oil cooled transformers & motors are checked for di-electric

4> TESTING & MAINTAINANCE

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- Oil cooled transformers & motors are checked for di-electric

strength of the oil.

- Check regularly sensitivityof ELCBs (30mA), and maintain

record.

- Electricians are given all regular safety gadgets like Helmet, Safety

Shoe, Safety Belt (for height work), Hand gloves .

- Gum boots are used during monsoon.

- Rubber hand gloves with suitable voltage rating used for work in

H-T lines.

- Rubber mats are placed in front of Panels. DBs.

5> PPE & SAFETY DEVICES

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- Rubber mats are placed in front of Panels. DBs.

- All portable hand tools, machines, extn. Boards are supplied

through RCCBs.

- Circuit breakers, Earth leakage relays are used as means of active

protection.

- Whereever fuses are used, correct rating and type is ensured.

Construction work is Tough, and the Construction work is Tough, and the

people who work in construction people who work in construction

need to be tough, but there is No need to be tough, but there is No

reason for them to be careless. reason for them to be careless.

Accidents can kill or permanently Accidents can kill or permanently

injure the tough as easily as any one injure the tough as easily as any one

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injure the tough as easily as any one injure the tough as easily as any one

else.else.

—H.R.H.Prince Philip

Duke of Edinburg

London

Any Questions ?Any Questions ?

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