11. CHAPTER - 11 Electrical Safety

8/19/2019 11. CHAPTER - 11 Electrical Safety

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CHAPTER - 11

Electrical Safety

1 Electricity, its Usefulness andHazards :

1.1 Usefulness1.2 Accidents & Hazards

2 Statutory Provisions :2.1 Factories Act and Rules2.2 Electricity Act and Rules

!ndian Standards.1 "ist of standards.2 #ational Electric $ode

. %A$ Reulations for ElectricalSyste'.

( Safe "i'its of Para'eters :(.1 P)ysioloy of Electric S)oc*s(.2 "i'its of A'+eraes(. "i'its of oltaes(.( Safe -istance fro' "ines(. S*in Resistance(./ Resistance of 0aterials

t)er Precautions for Electric or* .1 3eneral 0easures.2 0ain 'easures

/ verload and t)er Protections :/.1 Po4er $uttin -evices

/.2 %y+es of Protections :

/.2.1 $a+acity and Protectionof $onductors, 5ointsand $onnectors

/.2.2 verload and S)ort$ircuit Protection

/.2. Eart) Fault Protection/.2.( #o "oad Protection/.2. Eart), !nsulation and

$ontinuity %ests/.2./ Eart)in Standards/.2.6 Protection aainst

Sures and oltaeFluctuation

/.2.7 Hazards of 8orro4ed#eutrals

/. "i)tenin Arrester 6 Porta9le Electrical A++aratus7 Electric or* in Hazardous

At'os+)ere :7.1 $lassication of Hazardous

Areas7.2 Fla'e+roof Electrical

E;ui+'ent 7. 0easures 4it) "o4 & Hi) ris*

areas< Static Electricity :


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agricultural use pump+sets demand forwater etc. %n 199,+9- total 80 and in199-+9/ total 9., thousand million unitskwh electricity was produced. )uring199/+2002 in the 9th 3lan an increase of ,//./ 4W was recommended. 2,pri"ate power pro#ects of 11000 4W

capacity were sanctioned.

1.# Acci$e!ts % Ha&ar$s "

&ccident tables T ,./ ,.8 ,.20 and,.22 gi"en in 5hapter+, re"eal that in%ndia and 6u#arat electrical fatalaccidents are 7 2 to / of the totalaccidents. 4ode of fatal accidents due to

electricity is increasing. With the constantincrease of per capita consumption of electricity the chances of electricalaccidents may also increase. %t is alsoimportant to note that the accidents onlow "oltage 20 working are morethan that on high "oltage working anduntrained people are more in"ol"ed thanthe trained people.

&t U+)ar cinema hall in )elhi ,9 diedin *re due to electricity in 199/. Therefore10/ cinema halls restaurants and

ban'uet halls were gi"en notices on 2+/+9/ by the )elhi idyut (oard for "ariousde"iations from the 16 electrical safety conditions. &s per )elhi !ire :er"ice;sreport /0 of more than 2000 *resduring that period had occurred due tos)ort circuits


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than 2 and section / re'uireseDecti"e enclosure to sources of ignition.

Bule 8- of the Farnataka !actoriesBules 19-9 pro"ides as under@

GElectricity + 1 nder these rules the

consumer is responsible to maintain hiselectrical installation fully safe andcerti*ed. &n inspection by Electrical%nspector is also re'uired. !or details see3art 2./ I 2.8 of 5hapter+28.

+ INDIAN STANDARDS

+.1List *f Sta!$ar$s.

4any %: are a"ailable on electrical

safety such as @ 5urrent passing throughhuman body eDects 8/ )rillingmachines Cameproof for use in mines9192 fuses 208- 188 10-transformers :afety 11- lifts+dimensions , lighting *ttings +Cameproof 220- 3art 1 to safetyre'uirements for luminaries 191waterproof ,28 water tight ,, powerconnectors ,,-1 shock+e'uipment forprotection against 909 strength test for

solid insulating material 2,8 electricalaccessories ,1 apparatus and circuits

intrinsically safe ,/80 control de"icesoperating electrical apparatus /118Cameproof enclosures 218 for use ine?plosi"e gas atmosphere /-9 sparktest apparatus for 91-- testing -9appliances+household safety re'uirement02 connections for lighting *ttings

screwless -,8, for e?plosi"e atmosphere829 820 821 -91 /89 of machine tool 1,- installation +classi*cation of ha$ardous areas ,,/1,,/2 sand *lled protection of electricale'uipment //2 safe magnet telephonesfor use in ha$ardous atmosphere -,9safety for recti*er e'uipment --19insulating materials 8/-, 29 -/92en"ironmental tests 8999 9000 layout inresidential buildings -8 measuringinstruments for e?plosi"e gas atmosphere89, relays 82 ,8 21resistance+material test -, powerstations + *re safety 0 wiring /21-, 8/ 2--9 dust+proof electriclighting *ttings 012 dust+tight electriclighting *ttings 01 dust+tight ignitionproof enclosures 1100, Cash backCame arrester 1100- lightning arrester8,0 withdrawn building protectionagainst lighting 209 static electricityguide for control /-89 electro heat

installation safety re'uirement 9080guide for safety procedures and practicesin electrical work ,21- danger noticeplates 2,,1 earthing code of practice0 indicating instruments 128 10/919 induction motors 900 starters,12 switches push button /9 hea"yduty 0/ electrical e'uipment for use inmedical practice 8-0/ 3art 1 to 8warning symbols for dangerous "oltages892 safety re'uirement for measuringinstruments 929 safety re'uirements

for refrigerators food free$ers 10,2building for installation of electricapparatus for gas atmosphere rubbermats ,2 rubber glo"es //0 safety foraudio ampli*ers 101 electric wiring inhospitals // wiring "oltage e?ceeding-,0 "olts 22/ not e?ceeding -,0 "olts/2 o"erhead power andtelecommunication lines concrete poles/21 and portable methanometerelectrical type 99/.

!S:21/ + 6uide for :afety 3roceduresand 3ractices in Electric Work + 3art 1 @

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6eneral and 3art 2 @ Jife :a"ing Techni'ues must be followed strictly. &form of permit+to+work and specialinstructions while working with suchpermit are gi"en in 3art 1. >se of %: forha$ardous area classi*cation e'uipmentto be used in such area and earthing

practice are also recommended.:3 0 #ational Electric $ode

compiling many %: on electrotechnologyand :3 1 on treatment for electric shockare most useful for safety purpose. =therspecial publication :3 9 on low+"oltagesystems :3 8 on electric irons :3 9 onelectric water heaters :3 ,0 on electricradiators and :3 ,1 on electric sto"es arealso useful.

+.# Nati*!al Electric C*$eNEC "

This 5ode was adopted by the %ndian:tandards %nstitution on 1,+-+8 and was*rst published in &ugust 198,. %ts numberis :3@0+198.

The ob#ect as stated in the 5ode is tocomplement the %ndian Electricity Bules19,- by way of elaborating as well asrecommending practices to comply withtheir re'uirements. This 5ode is to

pro"ide information in a consolidated formto electrical engineers and contractors inthe country who are concerned with thedesign and operation of electricalinstallations. The sub#ect matter isdi"ided into the following se"en parts @

1. 6eneral and 5ommon &spects.2. Electrical %nstallation in :tandby

6enerating :tations and :ubstations.. Electrical %nstallations in

on the sub#ect.

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+.+ TAC Relati*!s f*rElectrical Syste/"

&bo"e regulations published by the TariD &d"isory 5ommittee 6eneral%nsurance (ombay has been framed toensure ma?imum safety to the insured

property from the risk of *re e?plosiondue to the use of electricity. To thate?tent these rules are diDerent from theElectricity Bules 19,- and other statutoryre'uirements. %t includes re'uisiteinformation from some %ndian :tandardsand gi"es in its &ppendi? E a list of someuseful %:.

These regulations apply to the entireelectrical system from the point of supplyto its use and co"ers all power

e'uipment switchboard powerdistribution and motor control geartransformer substation earthconnections wiring lighting *ttings andaccessories electrical e'uipment andapparatus and re'uirements of speci*coccupancies like godowns strong roomslifts petrol stations ha$ardous locationsmachine rooms high rise buildings etc.and testing.

The rules are comprehensi"e and incase of doubt it is suggested to refer the

T&5 (ombay.

0 SAFE LIITS (FPARAETERS

0.1 P2ysi*l*y *f ElectricS2*c3s"

!irst ma#or ha$ard due to electricity iss)oc* to a person. %t is the current not

"oltage that causes physiologicaldamage. (ut the current % "oltage Eand resistance B are inter+related by)'?s "a4, EK%B and therefore all thesethree factors are important to controleach other. 3ower W is WKE% andelectrical energy is the product of powerand time i.e. E%T and is gi"en by a Loule 1

LouleK1 ampere at 1 "olt for 1 second 1 Loule:ec is 1 watt and the practical unitfor energy is the kilowatt+hour and 1 FWAis e'ual to 1. A3 the Aorse 3ower an

another unit of electrical energy.

The blood is good conductor of electricity but the skin is highly resisti"e.>nless the skin is punctured no morecurrent will Cow through the body. (odyresistance of each person is "ariabletherefore eDect on them is also "ariable.>pto 10 m& current can be barred with

pain but at 0 m& chest muscles do notwork breathing stops and death mayoccur. 2,0 m& causes complete death.

Thus a leakage of 0.2, ampere isdangerous for human life. :ometimesafter+eDects are more se"ere than theactual shock or burn.

Electric S2*c3 is an eDect of acurrent Cowing through ner"es musclesheart or organs of a body. Electric shock issudden and accidental stimulation of thebody;s ner"ous system by electric currentwhich Cows due to "oltage diDerence.

The current may be )5 )irect5urrent or &5 &lternating 5urrent. )5may maintain in"oluntary grip on the li"econductor which prolongs the current Cow.

Therefore the "ictim needs to beseparated by a non+metallic rod orde"ice. 4ore )5 is re'uired than &5 tocause the same eDect. &5 produces*brillation e"ery cycle whereas )5produces only once.

Jow current disturbs body rhythmsometimes stops heart if time durationprolongs but high current causes electric4r!s and sometimes death.

:hock may happen due to@

1. 5ontact with bare li"e conductor.2. Bemo"al of insulation of a conductor

and its contact.. :hort circuit due to sudden failure and

the short circuit current not going toearth.

. :tatic charge on e'uipment dischargesthrough human body.

,. Jightening.

The se"erity of shock depends oncurrent "alue and the time of its passingthrough the body. 10 m& current can Cow, seconds through the body withoutdanger while 100 m& Cowing e"en for 1second could be fatal. %t also depends ontype of current &5 or )5 fre'uency

path of the current through body i.e.

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passing nearby the heart or other ner"ecentre.

3ersonal sensiti"ity to electric shock"aries from person to person. %t dependson age se? heart and wetting of skinwhich "aries the resistance of body. (utas the supply "oltage and fre'uency are

same throughout the country e.g. 20 ,0 cs and normal body resistance of a,0 kg or -0 kg man is also same for thee'ual condition the current "alues aredetermined by e?periments to *nd theireDects on body. These are stated intables in 3art .2

& woman;s body is more susceptibleto electric currents and the same eDectsmay be produced with 7 -0 the currentre'uired in a man. &t 0000 to 100000 csfre'uency the danger is less. )irectcurrent of 0., & and abo"e and a surge of oscillatory energy from 10 to 0 watt+seconds may pro"e dangerous. !or ,0 cs&5 current dangerous limit of "oltage are2 for children and -0 for adults. %nwet situation it is decreased :tatutorylimit is 2 .

The magnitude of the current Cowingthrough the body depends on the applied"oltage current is directly proportional to"oltage for the same resistance the

resistance of the path through bodycurrent is in"ersely proportional toresistance for the same "oltage and theresistance in turn depends upon the areaof the skin in contact with electrically li"eob#ect the moisture content of the skinmoist skin has low resistance allowshigh current and is more dangerous thandry skin and again the "oltage. Theresistance of body falls as the "oltage orcurrent is increased. :ee Table 11..

Te/5eratre % 2/i$ity increase

perspiration which makes the body wet. This decreases resistance allows highercurrent and is more serious condition.

(6ye! a!$ Car4*! Di*6i$e in airalso aDect. When o?ygen is less or5arbon )io?ide is high in the air bodyresistance reduces and the condition islike wet skin i.e. dangerous. The electricalha$ards for welders increase for thisreason.

Ty5e *f 7**ri! insulated

uninsulated dry or wet has direct eDect.

%nsulated and dry Coor is safer than theuninsulated conducti"e or wet Coor.

P*siti*! *f 4*$y 5arts in theelectric circuit through body is alsoimportant. %f both the hands or both thelegs touch li"e conductor the eDect ishigher. The most dangerous condition is

that of passing the current through heart.E8ect *! 2eart are serious. 20 to ,0

m& current passing through heart stopsthe heart so long as the current Cows.%mpurity of blood increases as the heart isnot working. %f this condition lasts for ,minutes or more irre"ersible damage iscaused to the brain as o?ygen is notreached there with the fresh blood whichmay pro"e fatal. %f the current isinterrupted before that and the arti*cialrespiration is promptly gi"en to the heartthe patient will mostly reco"er.

%f the current is increased to 80 to,00 m& the heart beat will stop ande"ery *bre of it will contract hapha$ardlycausing 94rillati*!. This will stop theentire blood circulation. E"en a "ery shortperiod of 0.1 second can cause thiscondition and if the current is stoppedafter 0.1 second the heart will ne"erreco"er and death results after a fewminutes. (ut it is possible to de*brillate

the heart by using a de"ice known as$e94rillat*r. (y this de"ice a countershock is gi"en to the heart which re"ertsthe heart muscles to their normal shape.Aowe"er such de"ice is a"ailable in thehospitals and the time factor is importantto reach there.

Electric 4r!s are caused due tohigh current Cowing through body. Aighercurrents cause electric burns #oule burninternal or Cash o"er or thermal burne?ternal and damage the ner"ous

system. Electric burns internally heat thebody not "isible from outside and arecurable by medical treatment. )ue tohigh "oltage and hea"y current sparkingtakes place and cloths also burn. Thiscauses thermal burns and if they aree?tensi"e the "ictim may die within fewdays.

&ccording to Loule;s law the heatgenerated is proportional to %2BT where %B and T are current resistance and time

respecti"ely. (urning takes place due toheat generated.

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When human body acting as earthedconductor comes nearer to a high"oltage conductor the air insulationbetween them break down and a spark isde"eloped between the two. Then currentpasses through the body to the earthcausing Cash burn.

%n addition to Cashing distance Cashburns can also be caused by hea"y shortcircuiting or opening of an isolatorcarrying hea"y load current.

!or degree and percentage of electricburns see 3art M 9 of 5hapter M -.

0.# Li/its *f A/5eraes"

!ollowing %: are most rele"ant@

%:@8/ 6uide on eDects of currentpassing through the humanbody @

3art + 1 6eneral aspects3art + 2 :pecial aspects

EDects of electric current on humanbody are summarised in Tables 11.1 to11..

Ta4le 11.1 " Crre!t ra!e a!$ e8ect *! a :; 3 /a!Crre!

t:<H&

P2ysi*l*icalP2e!*/e!*!

Feeli! *r Let2al i!ci$e!ce

1 m&


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800 100

O800 O100 >sually fatal

O1-00 O200 :e"ere burns se"ere *brillation and death

Ta4le 11.+ " E8ect *f electric crre!t *! /e! a!$ >*/e!Crre!t i! /A

DC :< H& AC 1


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Threshold of pain 1, Threshold of se"erepain

20

Threshold of hold+on 20 to 2, Threshold of death 0 to ,0 Bange of *brillation -0 to 2000

0.0 Safe Dista!ce fr*/ Li!es"

%t is ob"ious that o"erhead electriclines should not be allowed in a placewhere the public or public "ehicles ha"eto pass through for most of the time andnot at such a low or unsafe distanceclearance abo"e ground so that chancesof touching the lines may increase.

Therefore some minimum safe distance

from lines are necessary.Bules // to 80 of the %ndian Electricity

Bules 19,- pro"ide safety distances asgi"en in Table 11.,.

Ta4le 11.= " :afety distances of o"erhead lines

P*siti*! *f Li!es i!i//Dista!ce

Ft t Across t)e street :

4edium "oltage lines Aigh oltage lines

1920

,.8-.1

Alon t)e street :Jow I 4edium "oltage linesAigh oltage lines

18

19

,.,

,.8

Else4)ere :>p to 11 F lines bare>p to 11 F linesinsulated&bo"e 11 F lines&bo"e F lines

1,1

1/1/R1

fore"ery For partthereof

.-.0

,.2,.2R0.

fore"ery For partthereof

A9ove @ lines 9ut across or alon t)estreet

20 -.0

$rossin t)e tra'4ay or trolley 4ires :

)istances abo"ethe trolley wire

Jow I medium "oltage

lines 1.2

%f the wire is insulated>p to 11 F lines&bo"e 11 F linesE?tra high "oltagelines

2-8

0.-21.82.,

Passin a9ove,adacent or

ter'inatin on9uildins :

a Jow I medium"oltage lines+

10 .0

erticalclearance

8 2.,

Aori$ontalclearance

1.2

!or lessclearance thewire should beinsulated

b Aigh I e?tra high"oltage lines +

erticalclearance@

>p to F lines 12 ./

&bo"e Flines

12R1 ./R0.

for e"ery F orpart thereof

Aori$ontalclearance@

>p to 11 F lines 1.2

&bo"e 11 F Iup to F lines

- 2.0

&bo"e Flines

-R1 2.0R0.

for e"ery F orpart thereof

N*te @ %n abo"e table meaning of "oltagerange ur 2a" is as under @

Jow "oltage >p to 2,0

4edium "oltage >p to -,0 Aigh "oltage >p to FE?tra high"oltage

&bo"e F

Where an o"erhead line crosses or isin pro?imity to another o"erhead lineminimum clearances between them areprescribed ur 8/ and gi"en in Table+11.-

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Ta4le 11.: " Cleara!ces i! /etres4et>ee! li!es cr*ssi!eac2 *t2erSyste/)*ltae

11-::)

11<-1+#)

##<)

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and from low "oltage 2 to mains"oltage 20 .

%t is safe to assume a "alue of ,00ohms for dry work places and 200 ohmsor less for persons working in wetplaces. (ody resistance is practically $eroat high "oltages.

!or females and children the "alue of body resistance should be taken as half of that gi"en in Table+11.8 and for )5 the"alues of resistance should be considered times that of &5 for the same "oltages.

0.: Resista!ce *f aterials "

Besistance "alues for e'ual areas 10cm2 of "arious materials are as under @

aterial Resista!ce,*2/s

Bubber glo"es or soles 4ore than 204

)ry concrete abo"egrade

1+, 4

)ry concrete on grade 0.2+1 4Jeather sole dryincluding foot

0.1+0., 4

Jeather sole dampincluding foot

, F+20 F

Wet concrete on grade 1 F+, F

#ote : F K Filo ohms 4 K 4egaohms.

= (THER PRECAUTI(NSF(R ELECTRIC ?(R

:tatutory measures are alreadymentioned in foregoing 3art+2 which mustalways be followed with the help of %:mentioned in 3art+ abo"e.

:ome general and main safetymeasures are stated below@

1.1e!eral easres " They include +

1. 3roper earthing and double earthing.6eneral earthing for big power stationupto 0., ohm big substation 1 ohmsmall substation 2 ohm and tower andother places upto 8 ohms. )ue tominimum earthing resistance leakagecurrent passes through it and notthrough a person. The earthing should

be inspected tested and maintained

properly. There should be a regularpractice to check earthing. 4inimum"oltage between ground and theearthwire should be 0 .

2. >se of appro"ed insulated tools rubbermats shockproof glo"es and bootstester fuse puller or tong ).=. rod

discharge rod safety belt hand lampwooden or insulated ladder and notwearing metal ring chain etc.

. :witches on the li"e line. !usedswitches and air+current breaks shouldbe used.

. &"oid temporary wiring. &"oid hurryand chance taking. &"oid left handtouching.

,. Employ 'uali*ed and trainedelectrician.

-. Jow "oltage 2 &5 or 110 )5 inha$ardous area.

/. 6ood insulated and tested wiring.8. %solation of machinee'uipment before

use.9. Work permit system as gi"en in

%:@,21-+19-9. !ollow this %: forelectrical work.

10. :afety tags and safety warningnotices.

11. >se of machinee'uipment withintheir limits i.e. no o"erloading.

12. 3lacement of oil type transformeroutdoor.

1. &u?iliary room battery room andcontrol room to be separated.

1. Two e?its in each electric room.1,. :witch gear of the supply company

should be separated from that of theconsumer by a *reproof wall.

1-. 3recautions against thermal andmechanical stress moisture dust ando"er"oltage. &utomatic "oltageregulators and o"er"oltage relays

protect from o"er"oltages.1/. 6uard on transmission lines to

pre"ent fault due to birds.18. erminproof enclosure for indoor

switchgear.19. >se of electric shock guard EJ5(

and +pin plug and socket to ha"eproper earth connection.

20. >se of reactors or current limitingimpendences or underground neutralsto reduce fault le"els.

21. >se protecti"e relays circuit breakersand rated fuses to control the current

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and to isolate the faulty e'uipmentspeedily and automatically. 5heckbefore closing an =5( for high "oltagelines.

22. >se of grounding mat of low ohmic"alue and all non current+carryingparts to be connected to the grounding

grid by duplicate earth and segregatednon current carrying metallic parts tobe electrically bonded.

2. Becord of ground resistance "aluesand the physical condition of thegrounding mat.

2. Temperature sensiti"e alarm andprotecti"e relays to make alert anddisconnect e'uipment beforeo"erheating.

2,. %nterlocks to put into and out of ser"ice e'uipment correctly.

2-. Testing for high "oltage timingpolarity and insulation resistance.

2/. 5leaning and application of silicongrease to insulators to reduce pollutiondeposits.

28. :afe cable trenches and preferablyarmoured cables.

29. Transformers with oil safety ).=.fuse J.T. fuse 45( 455( andautomatic *re protection system.

0. 6enerators and motors with *re proof

doors automatically actuated by *redetectors.

1. Beady 5=2 type and other *ree?tinguishers.

2. )ouble communication systems withcritical areas.

. 5lear approach a"ailable for *re*ghting s'uad.

. !lame and shock detectors andcentral *re annunciation system for*re safety.

,. )iesel pump set for re'uired *re

water pressure.-. 6ood housekeeping including well

maintenance of all electricalinstallations.

/. &de'uate working space and meansof access around each apparatus.

8. !irst+aid bo?es and respiratorye'uipment ready. Training for arti*cialrespiration to sa"e life from shock.

9. 3re"ent higher humidity andtemperature near electric installations.

Work with full protection in raining.

0. >se of Cameproofe?plosion proof e'uipment in Cammablee?plosi"eareas.

1. Earthing and bonding of sol"entcarrying pipelines and e'uipment.

1.#ai! Safety /easres "

They include + 1. Is*lati*! @ Ji"e electric wiresparts

should be kept out of reach from thenormal working. :afety distancesmentioned in 3art . are one way of isolation. 5able trench is meant forisolation. %nstead of pro"idingtransformers on ground le"el Bt)iscondition in industrial estates and onroads any4)ere is 'ost danerousCthey must be placed at a safe height

with wire fencing. 3ro"ide segregationor a locked room if isolation is notpossible. 5ircuit breakers and powerisolation switches must be pro"ided atappropriate places.

2. I!slati*! @ Where isolation is notpossible and electrical e'uipment orwiring are on the working le"el cableconductors and leads should beinsulated with standard material.-ou9le insulation means pro"idingsecond layer of protecti"e insulation.

Then earthing is not re'uired. 3ortablee'uipment like electric sha"ers hairdryers hand tools are of this type.3ersonal insulation means to protectthe self by dry clothing rubber shoesrubber mat etc.

. Crre!t li/itati*! @ =nly limitedcurrent should pass through thee'uipment. E?cessi"e current shouldbe stopped. This is done by pro"idingfuses circuit breaker or isolators. Thesi$e of the fuse is important. %t shouldblow out when any short+circuit orearth current passes. & , amp fusedoes not mean that it will blow at ,amp. %t only means that it is capable of carrying current of , amp continuouslywithout getting hot. 6enerally fusesupto 10 amp rating are designed toblow at three times its rated "alue andthose abo"e 10 amp at twice therated "alue. Therefore it is unsafepractice to tie a thick or more wires in

a fuse. Then it may allow higher

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current e"en more than the ratedcapacity of the e'uipment anddamage it. :witches may burn andbecome black. Jow fuse "alue to limitcurrent is the simpler and cheapersafety de"ice.

. Eart2i! @ 3roper earthing is e'ually

important as fuses. %f an e'uipment isproperly earthed the higher earthfault or short circuit current will passthrough the fuse or circuit breaker tothe earth. This will open the circuit toprotect the e'uipment. Earthconductor should be checkedfre'uently for continuity and tightenedif found loose. 4a?imum permissibleearth resistance for diDerent fuse si$esare as under @

Fse A/5 Eart2 resista!ce i! *2//a6

, 1,.10 /.-20 ,./0 .8-0 1.9100 1.1200 0.,9

Thus earth resistance should be regularly

checked and maintained as perre'uirement.

=. L*c3*t a!$ Ta *t"Jockout and Tag out are generally

industrial practices indicating Qwarning;that the e'uipment or machine so lockedor marked shall not be used till that lockor notice is remo"ed.

Jockout means making thee'uipment machine inoperati"e orpower M isolated so that it cannot be

started or used. Jock label or notice of QJock+out; indicates that this e'uipmentor machine is faulty under repair ormaintenance and is locked for thepurpose of not using it till this lock ornotice e?ists.

Tag+out means to tie a tag on thee'uipment or machine to indicate that itis under repair or maintenance and not tobe touched or used. Tag out is mostessential when lockout is not possible. %t

can be used in addition to lockout forfurther precaution.

Jockout and Tag out procedure is alsore'uired to pre"ent accident fromune?pected starting or operation of anyswitch starter motor e'uipment etc.When some repair or maintenance work isto be started on electric line or some"essel pipe line etc source of supply of

power energy Cow etc needs to beisolated and for this purpose such switchle"er "al"e control knob etc should bekept in Qlocked oD; position by positi"elocking and tagging indicating instructionnot to open the lock or operate thatswitch "al"e etc.

When more than one departmentwants lockout of the same switch "al"ee'uipment etc each of them shouldapply their own lock and tagging. %n suchmultiple locking each key should bediDerent and no master keying should bea"ailable. %n case of diPculty lock maybe broken down but no duplicate keyshould be a"ailable.

3rocedure of lock out should beestablished. %t should include M1. (efore locking or tagging inform the

concerned operators and users thatline switch "al"e or e'uipment will beisolated or de+energi$ed and gi"e themtime to complete or stop their work.

2. 3lan the shut down and make thesystem oD.

. %nsert lock and attach tagging.. Test that the isolation is positi"e and

as per e?pectation.,. When repair maintenance work is

o"er open the locking and tagging.-. &gain inform the concerned people

that locking tagging is remo"ed andthat can work as usual.

:. (t2er Precati*!s @ These include

suPcient working space means of access proper lighting use of 33E!!E a"oidance of loose broken oropen wiring contact of metal partsand trained and competent personnel.While working on li"e conductor ore'uipment full slee"es are more usefulas dry cloth gi"es some protectionagainst shock. )on;t wear or keep anymetallic ornament or part with you.

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14/30

: ()ERL(AD AND (THERPR(TECTI(NS

%n industrial buildings appropriateprotection at switchboards anddistribution boards for all circuits and sub+circuits against o"er current and earthfaults is necessary. The protecti"eapparatus should be capable of interrupting any short+circuit current thatmay occur without danger. The ratingsand settings of fuses and the protecti"ede"ices shall be co+ordinated so as toaDord selecti"ity in operation wherenecessary. :etting of AB5 fuses should beproper. :upply of electric lighting andemergency ser"ices should be throughseparate main ser"ice and distribution

boards from the power circuits.4a#ority of electrical accidents can be

a"oided if 1 Ji"e parts are insulated ineDecti"e and durable manner andpositioned safely 2 5onducti"e parts of the e'uipment or machines should beearthed or double insulated and &llcomponents must be so dimensioned asto withstand design stresses

:.1 P*>er Ctti! Deices

ea!s *f Ctti! *f P*>er"

These are switches switch withfuses isolating links or circuit breakers.Where rapid operation is re'uired switchfuses and isolating links are not suitable.:eparate switches should be pro"ided totransformers motors and apparatus atcon"enient places. !or motors switchesshould be close to the starters. Jockingarrangement on switch or starterpre"ents accidental starting. %f locking is

not possible fuses should be taken outwhile working on that line. Earthing of conductors particularly of high "oltage oro"erhead lines is necessary. 4echanicalde"ices are clutches and belt strikinggears.

Restricti*! *! se *f S>itc2 *!Netral Eart2e$ C*!$ct*r "

& single pole switch should not be

placed in the neutral conductor of asystem which is connected to earth

e?cept for special purposes in generatingstations.

%f this conductor is bare e"en doublepole switch should not be placed in thisconductor e?cept for the purpose of breaking connection with generators andtransformers supplying the power. (ut the

connection with earth should not therebybe broken.

I/5*rta!t Safety ReGire/e!ts i!Desi! a!$ Use *f S>itc2es, S>itc2-Fses, Circit-@rea3ers a!$ Is*lati!Li!3s.

1. :uPcient capacity for making andbreaking contacts.

2. 5o"er for switch.. Aandle spindle should be a close *t in

the hole in order to pre"ent in#ury fromarcs inside. Aandle should beinsulated.

. G=nH and G=DH position in switches andcircuit breakers should be clearlymarked.

,. &mple space between opposite polesof double and multi+pole air breakswitches and circuit+breakers.

-. :hould make and maintain goodcontact on being operated without any

special skill or manipulation./. :witches and circuit+breakers should

be of such construction that theycannot be left in partial contact thatthere is speedy breaking of contactwhen operated to oD position. Thereshould also be other e?tra means of controlling the arc where necessary.

8. Aandle should be of suPcient si$econsistent with the eDort re'uired tooperate. %t should be insulated andearthed.

9. %solating links and switches withoutinsulated handles should be operatedby safe means such as by insulatedpoles.

:.# Ty5es *f Pr*tecti*!s "

:.#.1 Ca5acity a!$ Pr*tecti*! *fC*!$ct*rs, *i!ts

a!$ C*!!ect*rs "

14


15/30

&ll apparatus and conductors shouldbe of suPcient si$e and strength. Theyshould be co"ered with insulatingmaterial and placed or enclosed as topre"ent danger "i$. a 5onductors inconduit b 5onductors in Ce?ible metallictubing c 5onductors in metal trunking

d 5onductors with metal sheeting e%nsulated cables like .%.B. and 5.:.T.5ables f cables in trench.

="erhead trolley wires of cranesshould be 1 either protected by screenguards with suitable opening for tappingor 2 insulated cable self+winding drumsshould be used.

:crew cap lamp holders in which thescrew position of the holder and the lampcap are conducti"e should be *tted withsuitable shrouds or skirts or protected inany other suitable way.

Electrical #oints and connectionsshould be of proper construction asregards conducti"ity insulationmechanical strength and protection.

:.#.# (erl*a$ a!$ S2*rt CircitPr*tecti*! "

)anger from e?cess current due too"erload or short+circuit should be

pre"ented by pro"iding 1 !uses 25ircuit+breakers or Thermal protection.

3rotecti"e apparatus should be set ata low current "alue. Where time relays foro"er current protection are introduced asin the case of motors etc. possiblee?cessi"e temperature rise in e'uipmentand conductors should be considered. Thenumber of items collecti"ely protectedshould be limited to a"oid o"erfusing towithstand hea"y switching currents andto ensure subdi"isions so thatincon"enience from operation of protecti"e gear is not caused.

!uses relays and circuit+breakersshould be of suPcient breaking capacityto operate safely at short circuit currents.&rcing or scattering of hot metal of fusesmay be pre"ented by the use of impro"edfuses of cartridge or other type ha"ingspecial arrangements for e?tinction of arcat reduced current "alues.

Safety i! Re!e>al *f Fses *r Fsi!ele/e!ts

• =peration Without :witching =D @ Aere

switch+fuses are used. !or hea"ycurrent circuits switches should bepro"ided and operated before

operating the fuses.• =peration &fter :witching =D @ This is

the safest and should be the generalpractice. Be'uirements are @ a%nterlocking with switch b%ndependent switches to be accessiblec 5ombined switch and fuse bo?esshould ha"e li"e parts shrouded orprotected.

5ircuit+breakers where short circuit

current e?ceeds 10000 amperes or 1,04& should not be direct hand+operated.T2er/al Pr*tecti*! @ Thermal fuses

and relays operating on temperature riseare suitable for use with circuit orappliances where the fault current doesnot e?ceed the load current or wheresmall o"erloads can cause burn out.

E?amples are @ 1 5hoke coils of Cuorescent tubes 2 !ractionalhorsepower motors Badio sets.

E'uipment such as motors which

re'uire hea"y starting currents can beeDecti"ely protected by thermal relays.

:.#.+ Eart2 Falt Pr*tecti*! "

Pr*tectie Eart2i! "

&ll non+current carrying metal parts of electrical e'uipment should be earthed.:uch parts are @ 1 4etal conduits busbar steel trunking and cable sheets 2


16/30

6ood earthing can be achie"ed byconnecting earth continuity conductor to @

1. :heath and armour of GsupplyH cablewhene"er a"ailable.

2. %n the case of supply from owntransformer to a hea"y section copper

wire running to the neutral point of thetransformers and

.


17/30

current depending on winding resistance.With the same resistance if the "oltage isreduced it will reduce the current. %n suchcondition the use of fuses as a trippingde"ice is generally preferred.

%n low "oltage system if the circuit isdirect current type or hea"ily loaded the

slow operation of fuses low current oftenresults in arcing or Casho"er followed byburning of the contacts and this isdangerous for ser"ice personnel.

Therefore they should be protected byfollowing measures.

1. Employ trained electricians and gi"ethem full information regardingpossibility of arcing from fuses.

2. Aandles of the switch or fuse+bo?should be insulated. Jeather hand+glo"es up to elbow should be gi"ento workers.

.


18/30

system. This system has the widespreaduse in the world.

Earth resistance should be kept low tokeep the earth temperature low.

Therefore earth resistance should beperiodically checked and maintained.

%nsulation and continuity tests are

necessary to ensure that insulation"alues are within safe limits and thecircuit is continuous unbroken andwithout e?cessi"e leaks. %nstruments area"ailable for such tests.

:.#.: Eart2i! Sta!$ar$s "

%:@0 5ode of 3ractice for Earthing and:3 0


19/30

5opper -., mm2

&luminium 10 mm2

:teel or 6% 1- mm2

The bed plate should be securelyfastened by a bolt.

1 Earthing of portable appliance andtools should be continuous i.e. notwisted or taped #oints should be usedin earth wires. & single pole switchshould not be connected in earthconductor. !i?ed wiring at applianceinlet terminals must be done correctlyand as per %:. &ppliance ha"ing doubleor reinforced insulation need not beearthed.

!ollowing rules of the %ndianElectricity Bules 19,- are rele"ant onearthing standards @

Rle S4ect2 %denti*cation of earth

conductors. Earthed terminal on consumer;s

premises.,1 3ro"isions for power

installations.

-1 5onnections with earth.-1 & Earth leakage protecti"e de"ice.-2 :ystem at medium "oltage.-/ 5onnection with earth.-9 3ole type substations.

88 2 6uarding.90 Earthing.

:.#. Pr*tecti*! aai!st Sresa!$ )*ltae Flctati*! "

When e'uipment is switched onmomentarily initial e?cessi"e currents areknown as crre!t sres *r tra!sie!tcrre!t.

:urges may be more in starting coldcircuits than the hot circuit i.e. restartingof the pre"iously li"e circuit which wasclosed for a short while. !or e?amplewhen large banks of *lament lamps areswitched on current surge arisesbecause they ha"e much lower resistancewhen cold than when hot. %f a li"e lamp

circuit is made oD and soon reenergised

it will face fewer surges. Therefore fuse orcircuit breaker rating should consider thissurge phenomenon or its eDect gi"en as%2t where % K current t K time and S%2tknown as pre+arcing of a fuse or letthrough of a fuse or circuit breaker orwithstand of a component e.g. diode.

5urrent surges are also producedwhen large banks of condensers areswitched on. !or e?ample if thecondensers ha"e retained a charge of there"erse polarity and its circuit isenergised at the moment of ma?imum"oltage a "ery large charging current willCow. When condensers are switched forpower factor correction or tuning on highfre'uency furnace installations highsurge current Cows. To pre"ent damagelarge AB5 fuses are sometimes placedbetween sections.

:witching large power transformers orstarting up motors dri"ing high inertialoads also cause large current surges if closure occurs near ma?imum "oltage. %tis therefore important to ensure that themotor and starter are both suited to theduty. !ailure to do this may cause themotor to burn out or the starter toe?plode.

)uring surge current S%2t denotes a

measure of the damage or the s+ecicenery of the operation and can bede*ned as the energy dissipated as heatduring a speci*ed operation per ohm of resistance. Therefore for protectionagainst surges "alues of the protectingde"ice should withstand S%2t "alue. Thiscan be dealt with in the light of e?perience by increasing settings andfuse si$es. %t does howe"er militateagainst close protection.

)*ltae 7ctati*! from the

electricity supply lines has become acommon phenomenon at many places.:upply "oltage goes down resulting inreducing speeds of fans motorsmachines etc. and reducing lamp lighting.&gain it comes and stabilises thecondition. :uch "oltage Cuctuation if onhigher side may blow fuses or protectionand if on lower side reduces theproducti"ity or eDect of e'uipment.

&utomatic "oltage regulator or

"oltage stabiliser either built+in with thee'uipment mostly with household

19


20/30

appliances like free$e T etc. or e?ternalare readily a"ailable.

oltage Cuctuation on either side isharmful. %t accelerates or deceleratesspeed of machine or production. %tdamages furnaces by o"er or underheating. %t increases or decreases

lighting "entilation "oice etc. and manypower dependent parameters. 5hange intemperature aDects reaction rate inchemical processes. %t aDects radio Tcomputer hand tools and many homeappliances. ="er "oltage causes o"ercurrent which may increase the intensityof shock and Casho"er. Electric motorsfuses starters switches wiringinsulation may burn due to o"er "oltageand o"erheating. Therefore o"er "oltageor under "oltage must be pre"ented byappropriate automatic "oltage regulatorsor by power cutting de"ices. :ee part -for o"erload and other protections.

Tra"elling "oltage surges may beattenuated by surge absorbers which aredesigned to dissipate energy by eddycurrents andor hysteresis loss or by asuPcient length of cable. ="er+"oltagescan be relie"ed by spark gaps or by"arious de"ices which are insulators atnormal "oltages but breakdown at a

prescribed o"er+"oltage. They may or maynot be Qself healing;.

oltage spikes caused by currentchopping may be a"oided by a properchoice of cartridge fuses and otherssuppressed by shunt connected silicon orother semi+conductors for power circuitsand $ener diodes for light current circuits.

The possibility of Cash o"er in high"oltage trifurcating bo?es on transformerswitchgear or motors is pre"ented bybetter insulation *lling techni'ues andor

phase separation.)isconnected o"erhead line in the

pro?imity of other o"erhead lines shouldalso be kept earthed otherwise it maycause shock due to "oltage induced in it.

:.#.; Ha&ar$s *f @*rr*>e$Netrals "


21/30

for both the phase and the neutral toa"oid the ha$ard.

:.+Li2t!i! Arrest*rs "

Pe!$i!

P(RTA@LE ELECTRICALAPPARATUS

3ortable electrical apparatus do causemany accidents. 4etal+cased apparatus

are often held *rmly in the hand bypersons whose foot usually make goodcontact with Coor or metal work. TheCe?ible cables are sub#ect to muchbending rubbing and hard use. Theappliances or tools are sub#ected to"ibration and rough treatment in use. %nthose circumstances special precautionsare re'uired in installation maintenanceand use of portable apparatus.

Ca4le a!$ C*!!ecti*!s @ 3ortable

apparatus to the system should ha"eePcient permanent #oints connections orconnectors.

The cable should be reinforced at theplace where it enters the plug with stoutrubber tubing or metallic spiral. The cablegrip should be such that outer co"ering orsheathing is securely held and no strain isplaced on conductors. Aand shield disc orother types of guard between grip orhandle part and the portion containingcable and contact pins should be

pro"ided. pin protecti"e plug and socketshould be used.

Eart2i! I!slati*! @ &ll non+currentcarrying metal parts of portableapparatus and pendant lamps should beearthed unless suitably co"ered withinsulating material. The Ce?ible metalco"ering of conductors should also beearthedN but it should not be the meansof earthing the portable apparatus as theresistance of such metallic co"ers arehigh.

Jamp holders of portable lampsshould not be in metallic contact with theguard or other metal work. They shouldbe insulated and the other metal partsearthed. !or use near li"e conductorshand lamps ha"ing completely insulatede?terior and guards should be used.

!or use in dangerous situations suchas inside of boilers or tanks or damp ande?posed positions low "oltage lamps ortools should be used. & pressure of 2"olts with 12 "olts to earth isrecommended.

Earthing resistance should bechecked fre'uently and where"er it isdiPcult to obtain a low resistance othermethods of earth fault protectiondescribed earlier e.g. EJ5( should beused in addition. :ystems ha"ingmonitoring current which will trip thesupply if there is break in the earthconnection or if the resistance is highpro"ide ade'uate protection.

:ee 3art -.2.- for earthing I portableappliances para+1.

P*rta4le Tra!sf*r/ers @ The mainha$ard with metal cased portabletransformers is that if the earth wirebecomes detached in the mains+plug andtouches li"e wire the secondary neutral

and the metal case will be raised tophase "oltage of the mains. Theapparatus will thereby be charged tophase potential. The remedies are @ 15onstant inspection 2 3ro"ision of GstationsH with two separate earthedsockets one for mains supply from thetransformer Transformer withinsulated casing.

3ortable apparatus operating at low"oltage e.g. 110 are more safe thanthose operating at higher "oltage.

; ELECTRIC ?(R INHAZARD(US

AT(SPHERE

;.1 Classi9cati*! *f Ha&ar$*s Areas "

%n chemical petrochemical re*nery andfertiliser factories and also in coal mines

combustiblee?plosi"e dust "apour and

21


22/30

gases may e"ol"e during normal orabnormal operating conditions.

These gases coming into contact withair make an e?plosi"e air+gas mi?turewhich is ha$ardous to the installation of electrical apparatus as well as to theworkers.

%:@,,/2 di"ides the ha$ardous areacontaining Cammable gas or "apourcapable to be ignited into following three$ones for the purpose of appropriateelectrical installation @

Z*!e < Areas @ Aere ha$ardousatmosphere e?ists continuously "i$. the"apour space of closed process "esselsstorage tanks or closed containers. &nyspark will certainly lead to *re ore?plosion. Therefore any electricalapparatus in this $one must aDord anabsolute protection. %t is recommendedthat the use of electrical apparatusshould be a"oided in this $one but whenit is not practicable %:@,,/1 6uide forselection of electrical e'uipment forha$ardous areas should be followed.

Z*!e 1 Areas @ Aere ha$ardousatmosphere is likely to e?ist at any time.

Therefore the fullest practicablemeasures should be applied to pre"ent aha$ardous electrical condition at any time

and in any circumstances. Becommendedtypes of electrical apparatus and wiringfor use in Vone 1 areas are gi"en in%:@,,/1.

Z*!e # Areas @ Aere ha$ardousatmosphere is likely to occur only underabnormal operating conditions. Thisclassi*cation is applicable only where a*re or e?plosion ha$ard is unlikely andmay be caused only by the simultaneousand improbable occurrence of an arc orspark resulting from an electrical failure

and a ha$ardous atmosphere arisingthrough failure of the conditions of control. %t presupposes that anyha$ardous atmosphere resulting from anabnormal occurrence is rapidly dispersedso that possible contact with theelectrical apparatus is of minimumduration. &ny situation which allows aha$ardous atmosphere to collect such aspit or trench although it may be in theopen air shall in itself be classi*ed as

Vone 1 area e"en though the surroundingarea is classi*ed as Vone 2. Where doubts

e?ist in any speci*c case a Vone 1classi*cation should be adopted.

:ee 3art 2.1, Electric installationBule 102 to 11, also of 5hapter+28 forha$ardous area classi*cation andselection of electric apparatus wiring etc.

;.# Fla/e5r**f ElectricalEGi5/e!t "

The types of protection generallyapplicable to electric motors for use inha$ardous areas are@

1. !lameproof or E?plosion proof Type+d2. %ncreased :afety Type+e. %ntrinsic :afety Type+i.


23/30

of internale'uipment

toweatherproof.5arefulmaintenance

%ncreased

:afety

e 2 5heaper

:uitable for allgases.Jonglife.

Be'uirescareful

installation

-81


24/30

(esides *re *ghting e'uipmentfollowing *re safety re'uirements are alsorecommended @

1 &rea upto /,0 m2

+ &utomatic *re alarmsystem

2 &reaabo"e/,0 m2

+ &s abo"e or automaticsprinkler

Befer 3art . for T&5 regulations.

J STATIC ELECTRICITY

J.1 Electr*static c2ares %$isc2ares"

%mportance of static electricity isincreasing with the increasing use of insulating plastic rubber chemicalspetrochemicals *lms and Cammablegases "apours and dusts.

The generation of static electricity isa surface phenomenon associated withthe contact and separation of dissimilarsurfaces. !riction is not necessary togenerate electrostatic charge howe"er itincreases the release of electrons and

production of ionised particles. 5onditionsnecessary for generation of staticelectricity are @

1. & means of electrostatic chargegeneration.

2. & means of accumulating the separatecharges and maintaining a potentialdiDerence.

. There must be discharge of theaccumulated charge to gi"e sensationor eDect of the static electricity. %f the

discharge i.e. separation is of ade'uate energy it will gi"e a sparkwhich can ignite a Cammablemi?ture.

Thus static charge is *rst generatedthen accumulated and lastly discharged.=ut of these three stages only last one is"isible.

:tatic charging may occur due to @

1. C*!tact c2ari! by two dissimilarmaterials in contact. 3lastic *lmspassing o"er metal rollers whichshould be earthed powders Cowingthrough duct or people walking o"ercarpets may become highly charged.

2. LiGi$ 7*> through pipes generates

charge due to adsorption of impurityions. This may readily occur when*lters are used with petroleumproducts.

. S5ray Electri9cati*!. !ragmentationof a li'uid surface produces chargeddroplets. :plash+*lling of a tank mayform a charged mist. %n a tankerincendi"e sparks may come fromcharged clouds generated by watersprays for cleaning. :team+leak alsoproduces charge on isolated metalwork "i$. nearby pipeline. 5=2discharge from a *re+e?tinguisher mayalso generate charge.

. C*r*!a c2ari!. erographiccopying and electrostatic paint orpowder spraying creates charge by airions.

,. I!$cti*! c2ari!.


25/30

J.# (5erati*!s a!$ac2i!es e!erati! staticc2are ":ome e?amples are as under M

A (5erati*!s K1. Walking on dry Coors.2. Touching and rubbing hand on

plastic hand rails.. !low through long pipe lines of

small diameter. %ncrease indiameter reduces static chargeas friction reduces of the sameCow.

. !low through *lters "al"es etc.,. :tirring of li'uid at bottom.-. :plash *lling of li'uids or high

"elocity Cow. !low of li'uid intotank.

/. Two phase li'uid I solid li'uid Igas or air gas and solid Cows.

8. Joose Coating ob#ects.9. !low of air steam wet or gas

through opening of hose or pipe.10. )irecting air Cow on or near

electronic e'uipment e.g.compressed air cleaning of dust.

11. 3utting or mo"ing syntheticmaterial on or near electronice'uipment.

12. 3utting on and oD with #erksynthetic shirt from the humanbody.

1. Joose Coating ob#ects.1. 3rocess of mi?ing or agitation.1,. Bapid Cow of powder palettes

tablets etc. through chutes orpipe.

@ ac2i!es1. Bollers or roller contact of

dissimilar surfaces or mo"ingbelt or con"eyor on it e.g. rubber

mill paper mill calendarmachine dryer rolls etc.

2. Bunning of non conducti"e Catbelts on pulleys or rolls.

. 3ul"eri$ing machine wherepul"eri$ed materials passes onsurfaces.

. Jong con"eyor belts mo"ing onsupport rollers.

,. !eed hoppers and silos wherematerial slides on surfaces.

J.+ Ha&ar$s a!$ C*!tr*ls "

:tatic electricity is fre'uentlygenerated but mostly it is not ha$ardousbecause it is too weak or leaks oD as fastas it is generated. !or its fast leaking orbypassing good conductor antistaticde"ice is re'uired to connect the

charged surfaces with the earth.

J.+.1 Ha&ar$s *f Static Electricity "

&s rubber is bad conductor goodinsulator of electricity it accumulatesstatic electricity to a high degree. !ires inrubber industry are mostly due todischarge of such hea"y static charges.

%f e'uipment is not grounded staticcharge will continue to accumulate on ittill it will discharge as a spark. Thereforegrounding by a steel plate copper wire orbron$e brush is necessary.

Jightening form the sky is nothing buta discharge to the earth of enormousstatic charges generated andaccumulated between the layers of airand clouds in the atmosphere.

:ome speci*c ha$ards are as under M1. :hock if spark is not generated

and the charged surface not

grounded is touched by humanbody.

2. !ire or e?plosion if spark isgenerated due to discharge of static charge into Cammableatmosphere.

. Beadings are distorted orchanged in sensiti"e instruments.

. )ust deposition on chargedsurfaces.

,. 5logging or obstruction to freeCow of powders in chutes silos or

hoppers.

J.+.# C*!tr*l *f Static Electricity "

:e'uence to combat static electricityincludes following steps M1. 3re"ent charge generation.2. %f this is not possible pre"ent its

accumulation.. %f this is also not possible pre"ent

discharge from being ha$ardous

and

25


26/30

. 3re"ent formation of Cammableatmosphere near possibility of static electricity.

4ostly step+1 is not possible but step+2 can be implemented eDecti"ely byensuring earthing and bonding. !or step+ diameter of pipehole is increased Cow

rate is decreased etc.When two unlike materials separate

'uickly static charge is generated at thepoint of separation. 6round wire shouldbe attached where static charge is likelyto occur. !or proper ground connectionspring type or screw type clamp is used.6round clamps are made of materials likestainless steel or beryllium copper alloybecause they are good conductors of electricity and also non+sparking. 5lampsshould ha"e sharp points and enoughpressure to hold it *rmly.

5oating of paint rust corrosiongrease oil resin etc should be remo"edat a point where ground connection is tobe made. Thus grounding surfaces shouldbe made clean if they are not.

Joose connection broken clampbroken wires and unclean metal surfacesshould be checked before starting thework. 6round wire must be attached lastafter making sure that all connections are

made properly.%t is important to note that it is more

ad"isable and simpler to a"oid ha"ing aCammable atmosphere than to try forcharge a"oidance. !or this purpose inertgas *lling is *rst re'uired. :ome speci*ccontrol measures are as under@

1. Earthing grounding and bonding of e'uipment pipe #oints Canges andparts.

2. %ncreasing the conductance of Coors

footwear wheels and tyres forpersonnel and mo"ing e'uipment.

. %ncreasing the conducti"ity of non+conductors by conducti"e additi"essurface layers *lms and humidi*cationof the atmosphere.

. %ncreasing the conducti"ity of theatmosphere by ionisation.

,. >sing antistatic and conducti"ematerials and static eliminators.

-. Earthing of mo"ing machinery.

/. >se of antistatic belts or antistaticdressing to non+conducti"e belts atregular inter"als.

8. &ll tanks "essels pipelines containingsol"ents or Cammable li'uids or gasesshould be separately earthed. (ondingof pipe lines at Cange #oints necessary

unless metallic contact continuity isin between the Canges. Thus bondingis not re'uired for wholly metallicconnections not ha"ing resistance toearth more than 10 ohm. Aowe"erbonding is necessary if non metallice.g. plastic rubber asbestoscomponents are there in between the

#oint.9. Tank wagons and road tankers should

be earthed while loading or unloadingwith Cammable li'uid or gas. Bail+trackshould be earthed and #umpers to bepro"ided to connect rail to rail.

10. While pumping Cammable li'uids intanks the inlet pipe should e?tend anddischarge at the bottom of the tank. &long feed inlet pipe or inner limpetfor this purpose is desirable. &t thistime it is ad"isable to maintain aninert gas blanketing. !low "elocityshould be restricted.

11. The pipe and no$$le of steam or

water should be bonded while tankcleaning or steaming.

12. Ji'uid spillage and dust depositsshould be remo"ed as early aspossible.

1. 6ood "entilation and goodhousekeeping are necessary topre"ent Cammable concentration.

1.


27/30

transferring a product of two phasessuch as immiscible li'uids etc. The most rele"ant %: /-89 on control

of undesirable static electricity should bereferred for topics gi"en therein. Theyinclude de*nitions electrostatic chargetheir physiological eDects discharges

electrostatics in li'uids powders solidsand gases eDect on personnel earthingand bonding use of tanks + metallic Inon+metallic roadrail tanker smallcontainers transfer of li'uids pipelinesrelease of gases spraying of paints andpowders handling of electro+e?plosi"ede"ices earthing of personnel andha$ards from clothing.

!or earthing and bonding ma?imumearth resistance recommended is 10 ohm.&ntistatic or conducti"e type materialscan be used to a"oid the retention of static electricity. Earth resistance forstatic charge dissipation should beregularly checked.

1


28/30

design may be rewarded with lot of sa"ings at low cost.

!or an eDecti"e energy sa"ingprogram a well trained team of plantpersonnel is the *rst and foremostre'uirement. Xou too can achie"e JargeEnergy :a"ings by e?posing your

managers and engineers to the ideas andmethods of i'+rovin enery eDciency.

&n electrical energy conser"ationtraining programme may include followingor similar sub#ects @

1. :ystems &pproach to EPcient >se of Electricity.

2. Energy &ccounting 4onitoring I5ontrol.

. 4ethods for Energy EPciency%mpro"ement.

. Electric 4otors:tartersEPciency Testing 4ethods.

,. 3umps I !ans.-. ariable :peed )ri"es./. Electric Aeating4elting.8. Thermal %nsulation.

9. Electrolytic 3rocesses.10. %llumination.11. 5ompressed &ir.12. Befrigeration.1. 5ooling Towers.1. 4a?imum )emand3ower !actor

5ontrol.

1,. Transformers I 5able Josses.1-. 5ogeneration.1/. 4anagement of Energy 5onser"ation.18. 5ase :tudies.19. %nformation on :uppliers.

&s a result eDecti"e measures shouldcome out as minimum energy inputssa"ings of electricity heat steam waterair etc. and optimum use of controlledenergy.

4aharashtra 6as 5racker 5omple?%35J


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1-. What are current surges Y Whendo they occur Y What are theprotections against them Y

1/. E?plain neutral connectionsystem and safety aspect of it.

18. What do you mean byQlightening arrestor;Y E?plain its

arrangement and working.19. E?plain the safety aspects of

portable electrical apparatus.20. :tate %ndian :tandard and its

classi*cation of ha$ardousareas for electric work.

21. E?plain type of Cameproof electrical e'uipment necessaryfor three classes of ha$ardousareas.

22. Jist diDerent types of Cameproof e'uipment ande?plain the utility of any 9e of them.

2. E?plain the phenomenon of static electricity and types of static charging.

2. E?plain where bonding is notnecessary to protect from staticelectricity Y

2,. :tate "arious operations andmachines generating staticelectricity.

#:. ?rite s2*rt N*tes "1. Type of electrical

ha$ards.2.


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8. Electrical Earthing and &ccidents3re"ention 4.6. :ay 6eorge :&.

10. %ndustrial Wiring 3olyako" I

Fo"arsky 3rogress 3ublishers 4oscow.

11. &ccident 3re"ention 4anual for%ndustrial =perations :&.

12.

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11. CHAPTER - 11 Electrical Safety