electric wiring

1. HOUSE WIRING

2. SelectionoftheWiringSystem
The followingpointsshouldbeconsideredinselectingawiringsystemsoastoincreasethe
safetyofhumanlife:
(i) Distancefromfirepoints.
(ii) Separationfromwaterormoisture.
(iii) Protectionfrommechanicalthrusts.
(iv) Protectionfromratsandwhite-ants.
(v) Thetypeofbuilding.
(vi) Thecostofwiring.
(vii) Durabilityandpleasingappearance.
(viii) Safetyfromelectricshocks.

3. MaterialRequiredforWiring
Thefollowingmaterialisrequiredforthewiring–
1. ElectricalAccessories
2. Wires
3. Woodenscrews
4. PorcelainorP.V.C.pipe
5. WoodenBoardandPlugs
6. Distributionboard
7. Mainswitchboard
8. Meterboard

4. PreparationofWiring
Thefollowingstepsaretobetakenbeforestartingthewiring,soastomakethejobeasy.
1. ToPrepareWiringDiagram
2. ToEstimate
3. Marking
4. ToFixtheWoodenorRowelPlugs
MethodsofWiring
Thethreemainmethodsofwiringareasfollows:
1. Loopingmethod
2. Connectormethod
3. Treemethod

5. Loopingmethod– Thismethodofwiringisjointless.Separatephasewiresaretakenfor
eachcircuitfromthedistributionboxdirectly.Theneutrallineremainscommonforallthe
circuitsasshowninFig.11.8.Ifanextensionisrequired,thenitwouldbetakenfromthe
distributionboxorfromaceilingrose,socket,switchetc.butitwouldnotbetakenbymakinga
jointintheline.

7. Advantages
(i) Itlooksbeautiful
(ii) Itisjointless
(iii) Ithasahighinsulationresistance.
Disadvantages
(i) Itrequiresmorewire.
(ii) Itisexpensive.
(iii) Itrequiresmorespace.

8. 2.ConnectorMethod – Inthismethodconnectorareusedmidwaybetweenthe
Wiring.Connectorservesasdistributionjunctionforthephaseswellasfortheneutralline,as
shownin.Aconnectorisfittedovereachjoint.
Connector

9. Connector
N
P
Connector

10. Advantages
(i) Itrequireslesswire.
(ii) Itisinexpensive.
(iii) Ithasalowvoltagedropintheconductingwire.
(iv) Itcanbeinstalledpromptly.

11. Disadvantages
(i) Thejointsmayremainloose.
(ii) Itdoesnotlookbeautiful.

12. 3. TreeMethod – Inthismethod,manybranch-linesaretakenputfromthemain-
Linelike,a-treeasshowninFig.11.10.Eachbranchlineworksasaseparatecircuit.The
methodisalsoknownasmaindistributionmethod.Thecurrentcarryingcapacityofthemain-
linewireiskeptsufficientlyhigh.Thecurrentcarryingcapacityofthebranch-linewireiskeptin
accordancetotheload.Thefusecut-outisplacedonthemain-lineonly,thusifanybranch-
lineisfaultythenthewholelinehastobeswitchedoff.Thistypeofwiringisinstalledonboard
aship,infairs,exhibitionsandotherdecorativeplaces.

14. Advantages
(i) Itrequireslesswire
(ii) Itcanbeinstalledeasily.
Disadvantages
(i) Itdoesnotappearbeautiful.
(ii) Ithasahighvoltagedrop.
(iii) Fault-tracingisnoteasyinit.
(iv) Thewholelinehastobeswitchedoffduringfaulr-tracing.

15. Advantages,Disadvantages,UsesandPrecautionsRegardingVariousDomestic
Wirings
1. Temporarywiring
(i) Flexible-wirewiring –V.I.R.orP.V.C.wiresareplacedinsidetheconduitpipesasper
wiring-diagram.Forpassingthecablesthroughtheconduitpipes,aguide-wireisused(usually
barecopperwire).Thecablesarefastenedtotheguidewire,anditisthenpolledfromtheexit-
end.ThesystemofconduitpipeswiringisshowninFig.11.16
Conduitpipeswiringhassufficientmechanicalstrength,anditisleastaffectedbymechanical
thrusts,fire,atmosphericeffectsetc.

16. DuctWiring – Itisalsoknownasconcealedwiring.Forthiswiring,groovesaremadein
thewallsandfloorasperwiring-diagram,andthentheconduit-wiringisplacedinthegrooves.
Theconduitpipesareproperlyfittedinthegroovesbyusinghooks.Thesearepaintedwith
enamelpaints,soastoprotectthemagainstrusting.Thenecessaryaccessoriesarefittedand
thentheearth-wireisclipped.Finally,thewiringiscoveredwithcementplaster.Inthenew
buildings,conduitpipesareplacedinsidethewallsasperwiringdiagramduringthe
construction ofthebuilding.Onlyinspectionboxes,junctionboxes,roundblocksandswitch
boardsremainvisibleoutsidethewallsandceiling.
Thewiringlooksbeautifulastheconduitpipesremaininvisible.Itislonglasting,hencethe
systemisutilizedincinemahalls,hospitals,officesandresidentialbuildings.Nowadays,
P.V.C.pipesarealsousedforconcealedwiringinplaceofironpipes.

17. Advantages
(a) Itcanbeinstalledwithinashorttime.
(b) Itiseconomical.
Disadvantages
(a) Itisnotlonglastinganditmaybeinstalledforaperiodofnotmorethan
sixmonths.
(b) Thejointsmaygetopenwithinfewweeksonly.
(c) Thewireusedinthewiringdeterioratesrapidly.
(d) Thepossibilityofanelectricshockisalwayspresentinit.

18. Uses
(a) Itisusedfordecorationpurposesinmarriages,exhibitions,fairetc.
(b) Itisusedforextensionoftemporaryconnectionsinvariousbuildings.
Precautions
(a) Itshouldnotbeinstalledinworkshops,showrooms,shopsandotherpublic
Places.
(b) Thewireshouldbeclippedproperly,andshouldnotbeleftsuspended.
(c) Thewiringshouldbeinstalledatasafeheight.
(d) Itshouldbeinstallednearfire-points,gaspipes,metallicstructuresandwet
Places.

19. (ii)Clearwiring
Advantages
(a)Itiseconomical.
(b)Itcanbeinstalledeasily.
(c)Itsfaultscanbetracedouteasily.

20. Disadvantages
(a) Whenitswiresgetloose,thenitlooksugly.
(b) Itswirescanbecutrats.
(c) Itcaneasilybeaffectedbymoisture.
(d) Thepossibilityofleakageintowallsisalwayspresentinit.
(e) Thepossibilityofanelectricshockisalwayspresentinit.

21. Uses
Itisusedfortemporarywiringinsmallplaces,i.e.,shopsandresidentialbuildingforaperiod
ofnotmorethanoneyear.

22. Precautions
(a) Thewiresshouldbesufficientlystretched.
(b) Thewiringshouldbeinstalledatasafeheight.
(c) The cleatsshouldbefittedabout50-60cmapartfromeachother.
(d) Thecleatsshouldbefittedonbothsidesofabend.
(e) Thebendsshouldbemaderoundenough.
(f) Thecrossingofwiresshouldbeminimum.
(g) Itshouldnotbeinstalledneatfirepoints,gas-pipes,moistplacesand
Inflammablematerialssuchaspetroletc.
(h) Thenumberofjointsshouldbeminimum.

23. 2. Permanentwiring
(i)Casingcappingwiring
Advantages
(a)Itislonglasting.
(b)Itlooksbeautiful.
(c)Thepossibilityofshort-circuitingbetweenthephaseandneutralwiresis
Minimum.
(d) Thewiresremainssafeinsidethecasing-capping.

24. Disadvantages
(a) Itabsorbsmoistureveryrapidly.
(b) Itcatchesfireveryeasily.
(c) Itrequiresmorespace.
(d) Itsinstallationrequiressufficienttime.
(e) Itisexpensive.
Uses
Itisusedforlightandfanintheshopsandhouses.

25. Precautions
(a) Itshouldnotbeinstalledatdampplaces.
(b) Thecasingcappingshouldbecoatedwithvarnish.
(c) Roundporcelaincleatsshouldbeusedbeneathhecasingtoprotectitfrom
Moistureeffect.
(d) Itshouldbeprotectedfromwhite-antsbyusingseasonedteak-woodand
antiwhite-antsoil.
(e) Thewirejointsshouldhotbeloose.
(f) Solidwoodencornersshouldbeusedatthebends
(g) Theuseofabridgejointshouldbekepttoaminimum.
(h) Casingcappingshouldnotbeburiedundermasonrywork.
(i)Thecasing-cappingwoodshouldbefreefromknots,shakesoranyother
Defects.
(j) Forcrossingthewalls,conduitpipesshouldbeused.

26. ii) Battenwiring
Advantages
(a) Itisfreefrommoisture,atmospheric,acidicandalkalineeffects.
(b) Itcanbepassedthroughthewallseven.
(c) Itcanbeinstalledeasily.
(d) Itcanbeinstalledonoddsurfacesalso.
(e) Itrequiressmallspaceforitsinstallations.
Disadvantages
(a) Itisunsuitableforhotplacesortheplacesopentosun-rays.
(b) Itrequiresmorewire.

27. Uses
Itisusedinshops,hallshousesandotherbigbuildings.
Precautions
(a) The wiresshouldbeproperlystretched.
(b) Theclipsshouldbefittedatsmalldistances.
(c) Thenumberofwirejointsshouldbeminimum.
(d) Thewiresshouldbebenttotakesufficientroundshapeatthecorners.
(e) Thebattenshouldbecoatedwithvarnishwhenusedindampplaces.

28. (iii) Leadsheathedwiring
Advantages
(a) Itiswater-proof,henceitcanbeinstalledindampplacesalso.
(b) Itcanbepassedthroughthewallseven.
(c) Itisfreefromrains,sun-raysandheateffects.
(d) Itisfire-proof.
Disadvantages
(a) Itisanexpensive.
(b) Itrequiresessentialearthling.
(c) Ithasmoreleakagepossibilities.

29. Uses
Itisusedindampplacesandwherethewiringisnecessarilyrequiredtobewaterandfire
proof.
Precautions
(a) Theleadcoveringshouldbeearthed.
(b) Itshouldnotbeusedinsuchplaceswhereitcanbeaffectedbychemical
corrosion.
(c) Sharpbendsshouldbeavoided.
(d) Thecableshouldnothaveanyleakage

30. iv) Conduitpipewiring
Advantages
(a) Ithasgoodmechanicalstrength.
(b) Itisalmostfireproof.
(c) Itisfairlywaterproof.
(d) Sharpbendsshouldbeavoided.
(e) Thecableshouldnothaveanyleakage.

31. Disadvantages
(a) Itisexpensive.
(b) Itsinstallationrequiresskilledandexperiencedmechanics.
(c) Improperinstallationcanbedamagedbymoistureorwaterwhichhas
Enteredinsidethepipe.
(d) Theinsulationofthewiresmaybedamaged,iftheinstallationjobisnot
donewithcare.
Uses
Itisusedingodowns,cinemahalls,workshopandindustriesetc.

32. Precautions
(a) The earthwireshouldbeusedwithconduitwiring
(b) Thewaterorgasshouldbeawayfromconduitpipes.
(c) Theconduitpipesshouldbecutproperlyandtheirends shouldnotbe
sharp, sothattheymaynotturntheinsulationofthewires.
(d) Theconduitpipesshouldnotbemoistfrominside.
(e) Wooden-battenspacersbeusedtokeeptheconduitpipesseparatedfromthe
Walls.
(f) Guidewireshouldbeusedwhilewiring.
(g) Withtightgaugeconduitpipes,gripfittingshouldbedone,Whilewith
heavygaugeconduitpipesthreadedfittingshouldbedone.
(h) Onlythenecessarywiresshouldbepassedthroughheconduitpipes.

33. (v) Ductorconcealedwiring
Advantages
(a) Thebuildinginstalledwiththistypeofwiringlookbeautifulsincethe
Wiringremainsalmostinvisible
(b) Morenumberofwirescanbeconcealedtogether.
(c) Itischeaperthanconduitwiring.
(d) Itoccupiessmallspace.
(e) Itdoesnotrequirehighly skilledmechanics
Disadvantages
(a) Possibilitiesofleakageisalwayspresentinit.
(b) Earthlingisessential inthiswiringsystem.

34. Uses
Itisusefulforhospital,drawingrooms,highprecisionworkshopetc.
Precautions
(a) Conduitpipesshouldbewellpaintedbeforeburying themundercement
PlasterorP.V.C.pipesshouldbeused
(b) Thewiresshouldnottwistinsidethepipes.
(c) Anytypeofhammeringshouldnotbeappliedattheplacesinstalledwith
Conduitwiring.
(d) Thegroovemadeinthewallshouldnotbedeepandwideenoughsothatit
Mayaccommodatethepipealongwithathicklayerofcementplasterover
it.

35. I.E.orI.S.RulesRegardingWiring
Generalinstruction
IndianelectricityorIndianstandardinstructionsregardingvariouswiringsystemsareas
follows:
1. Anycircuitforlightandfanshouldnothavemorethan800wattsloadand
Shouldnotcomprisemorethan10points.
2. Theswitchandthefusecut-outshouldalwaysbeinstalledonthephaseline.
3. Theneutrallineshouldhaveneutral-linkonlyandnottheswitchorfuse
cut-out.
4. Allmain-switchesshouldbecoveredwithironsheetorinsulatingmaterial
Sheet.
5. TheneutrallineshouldbemarkedN.

36. 6. Aswitchmustbeusedforasocketanditshouldbeinstalledonthephase
line.
7. Afusecut-outshouldnotbeinstalledonthesocketline.Ifnecessary,thenit
shouldbeinstalledonthephaselineonly.
8. Theinstallationofsocketsshouldbebeyondthechildren’sapproachor
Otherwisetheyshouldbecoveredwithcoverplugs.
9. Thesocketsusedshouldbeof3-pintype,whosethickerpinshouldbe
Earthed.
10.Water-proofwiresshouldbeusedintheopenplaces.
11.Thethreephasesofapowerlineshouldbemarkedwithred,yellowand
BluecoluresandthephaselineusedforlightandfanshouldbemarkedP
AndtheneutrallineshouldbemarkedN.
12.AcautionplatewrittenwithDANGERshouldbehungnearthemain-
switch,ifthevoltageexceedsabove250volts.

37. 13.Theceilingfansshouldbeinstalledataheightof2.7meterfromthefloor.
14.Thewiringandthedistributionboardsshouldbeinstalledseparatelyforthe
Power,lightandfanlines.
15.Thewiringshouldbedoneontheceilingoronthewaltzneartheceiling.
16.Themain-switchboardshouldbeinstalledataheightof1.5metersfromthe
floor.
17.Allthewires,switches,fusesandotheraccessoriesusedshouldbeofcorrect
Currentcarryingcapacity.

38. InstructionforConduitPipeWiring
1. Theconduitpipesusedshouldbeofenamelpaintedtype.
2. Preferably,theconduitpipesusedshouldbeofheavygaugetype,andthey
shouldbeextendedbythreadedjoints.
3. Woodenbattenspacersshouldbeusedtokeeptheconduitpipesseparate
fromthewalls.
4. Preferably,thebends,tees,junctionboxesetc.usedshouldbeofinspection
type,excepttheextremeendbends.
5. Thethreatontheconduitpipesshouldbemadeuptoadistanceof12to25
cmfromtheends.

39. 6. Theprojectedorsharpendsoftheconduitpipesshouldbefiledsmooth.
7. Theinspection-boxshouldbeplacedinsuchawaysoastoenablethewires
tobeinspectedeasily,anditshouldbecoveredwithalid.
8. Thesaddles,shouldbefixedatabout30cmapartonbothsidesoabendor
Tee.
9. Thesaddles,usedforthefittingoconduitpipes,shouldnotbespacedmore
thanonemeterapartfromeachother.
10.Theearthingwireshouldbeclippedalongwiththewholelengthofconduit
Pipes.
11.Thefusecut-outandmain-switchesshouldbeplacedinclosedinsulated
covers.
12. Thethreadsoftheconduitpipesshouldnotbevisible,andshouldbefully
tiedintothebends,tees,junctionboxesetc.

40. InstructionforDuctorConcealedWiring
1. Thewidthanddepthofthegroovemadeinthewallshouldbekeptenough,
sothattheconduitpipesmaybehurriedinthemquiteeasily.
2. Allmetallicparts(exceptconductingwires)ofthewiringshouldbeearthed.
3. Theinspectionboxshouldbefittedinsuchawaythatitremainsvisible
outsidethecementplaster.
4. Thewiresshouldbeplacedintotheconduitpipesortakenoutofthemwith
thehelpofguide-wire.
5. Theswitchesetc.shouldbeclosedinmetallicinsulatedcovers,whiletheir
togglesremainoutofthecementplaster.

41. TestforWiringasperI.E.RulesbeforeSupplyingMains
Thefollowingtestsnecessarybeconductedbeforesupplyinghemainstoadomestic
installation,asperIndianElectricityRules.A500voltsmeggerisusedforthepurpose.
1.Insulationresistancetestbetweentheconductorandearth.
2.Insulationresistancetestbetweentheconductor.
3.Continuitytest.
4.Polarityoftheswitches.

42. 1. InsulationResistance Test betweenthe Conductor andEarth -

43. Thepurpose of thistestisomeasuretheinsulationresistancebetweenthewireandearth,so
astoavoidanypossibleleakageinthewiring.Thetestisalsoknownasleakagetest.
Aftercompletionof thedomesticinstallation,thetestisconductedinthefollowingmanner:
(i) Main-switchisswitchedoff.
(ii) Theinputphaseandneutralwiresareshortcircuited.
(i) TheLterminalofthemeggerisconnectedtotheabovejointandtheEterminalis
earthed.
(ii) Fuse-wiresareplacedinallthefusecut-outs.
(iii) Allthelampsetc.areputintheirpositionsandallthesocketandceiling-rosesareshort-
circuited.
(iv) AlltheswitchesareputtoON.
Nowthemeggerisoperatedgentlyanditsspedisbroughtto160r.p.m.Thepointer,
thenindicatesareadinginmegaohms.The readingshouldnotbelessthan:

44. Insulationresistance= 50megaohms
Numberofconsumptionpoints
Itisdesirablethatthevalueofresistancemeasuredshouldnotbelessthanonemegaohms.
Inthecountingofpoints,oneswitchplusoneholderiscountedasonepoint,whereasasocket
iscountedashalfpoint.
AsperIndianElectricityRules,theamountofleakagecurrentshould notbemorethan
1/5000th
partofthefullamount ofcurrentflowingthroughthecircuit.
Here,leakagecurrent= Supplyvoltage
Insulationresistance
Forexample,ifthesupplyvoltageis200voltsandtheinsulationresistance,asmeasuredby
themeggerisonemegaohm,then
Leakagecurrent=200 = 1 amperes
1*10 500

45. 1. InsulationResistanceTest betweentheConductor –

46. Thepurposeofthistestistomeasuretheinsulationresistancebetweenthephaseandneutral
wiresoftheinsulations,soastoavoidanypossibleshort-circuitbetweenthetwoconductor.
Thetestisalsoknownasshortcircuittest.Thephaseandneutralwiresremainseparateinthe
test.Thetestisconductedinthefollowingmanner:
a. Fuse-gripsareplacedinallthefusecut-outs.
b. Allthe switchesareputON.
c. Allthelampsareremovedfromtheirholders,andthesockets,ceilingrosesetc.arenotshort
circuited.
d. TheLterminalofthemeggerisconnectedtothephasewireandtheEterminaltotheneutral
wire.
Onoperatingthemegger,itsreadingshouldnotbemorethan–
500
______________________________
Numberofconsumptionpoints

47. 1. Continuitytest– Thepurposeofthistestistocheckthatthecircuitiscomplete ornot
forpassingacurrentthroughit.Itisconductedinthefollowingmanner:
a. Alltherose-gripsareplacedintheirfusecut-outs.
b. AlltheswitchesareputtopON.
c. Allthelampsareplacedintheirholders.
d. Allthesocketsandceiling-rosesareshort-circuited.
e. Themeggerisconnectedasperfig11.18
Onoperatingthemegger,itspointershouldindicateZEROforacompletecircuit.Ifthepointer
indicatesINFINITY,thenitmeansthatthe circuitisopen.Now,testeachswitchbyputtingitto
OFFinturn,andthepointershouldindicateINFINITYforeachswitch.Ifforanyswitch,the
pointerindicatesZERO,thenthecircuitofthatswitchissupposedtobeshort-circuited.Check
theparticularcircuitandremovethefault.

48. 1. PolarityTestoftheSwitches–
Thepurposeofthe testistocheckthattheswitchesareplacedonthephaselineornot.For
this,connecttheLterminalofthemeggertooneterminaloftheswitchandtheEterminalto
theneutralline.Ifthepointerofthe meggerindicatesZERO, thentheswitchissupposedto
beplacedontheneutralline.Repeatthetestofeachswitchandcorrecttheconnectionsofthe
faultyswitch.
Thetestisalsoknownassupplytest.Itcanbeconductedbyatestlampalso.Forthis,switch
onthemainsupplyandputtheswitchundertesttoOFF.Now,connectthetest-lampacross
theswitchterminalandtheearthpoint.Ifthetestlampglows,the switchissupposedtobe
placedonthephaseline,otherwiseithasbeenplacedontheneutralline,thencorrectthe
connectionsofthefaultyswitch.

49. GeneralFaultsofElectricalInstallations
Thegeneralfaultwhichusuallyariseinadomesticorindustrialinstallationareasfollows:
1. Shortcircuit
2. Leakagecircuit
3. Opencircuit
4.Fusewireburning
5.Earthing

50. 1.ShortCircuit–
Ifmeansthatthephasewireistouchingwiththeneutralwireanywhereintheinstallation.Due
tothisfaultaheavycurrentflowsthroughthecircuitandthefuseburnsout.Tilefaultthismay
betracedoutwithameggerasexplainedinart.
Thefaultcanbetracedoutwithatestlampalso.Forthis,pulloutallthefuse-gripsfromthe
distributionboardandput themain-switchtoON.Placeallthelampsetc.intheirpositionsand
putalltheswitchestoON.Now,connectboththeendsofthetest-lamptoboththeterminalsof
thefusecut-out.Testallthefusecut-outonebyone.Thecircuitonwhichthetest-lampglows,
isthefaultycircuit.
Tolocatetheplaceoshort-circuit,letthetest-lampbeconnectedtofaultyfusecut-outandput
alltheswitchestoOFF,thetest-lampwouldstoptoglow.Now,puttheswitchestoONoneby
one,thetestlampwillglowbyswitchingonthefaultycircuit.The faultofthatparticularcircuit
canberemovedbycheckingitswirescarefully.

51. 2.LeakageCircuit
Ifthemain-metercontinuestoberunningevenonputtingalltheswitchestoOFF,thenthere
isleakagefaultinthecircuit.Thefaultmaybetracedoutwithameggerasexplainedinart.
Thefaultcanbetracedoutwithatest-lampalso.Forthis,connectoneendofthetestlampto
theneutral,andtheothertotheearthline.Ifthetest-lampglowsalittle,thenthereisleakage
faultinthecircuit.Now,openthejointsoftheneutralwireandrepeatthetest.Byhitandtrial
method,thefaultcanberemoved.

52. 3.OpenCircuit
IfalampdoesnotglowevenbyputtingitsswitchtoON,thenthereisanopen-circuitfaultinits
wiring.Thefaultarisesduetolooseningofawirejointorduetobreakingofanywire.Thefault
canbetestedwithameggerinthewaysimilartocontinuitytest,butrememberthat linemust
beswitchedoffforthetestotherwisethemeggerwillbumout.
Totestthefaultwithatest-lamp,connectoneendofthetest-lamptooneterminalofthe
switchandtheotherendtoaterminaloftheholder.Thecircuitinwhichthetestlampdoesnot
glow,isthefaultycircuit.
Checkitswiringandremovethefault.

53. 4.FuseWireBurning
IfthefuseburnsoutonputtingthemainswitchtoON,thenthereisshort-circuitfaultinthe
installationwhichcanberemovedasexplainedinart.Ifitburnsonincreasingtheload
gradually,thenthecircuitissaidtobeoverloaded.Since,thecapacityofthefusewire
dependsontheloadtherefore,bydecreasingtheloadorincreasingthecapacity ofthefuse
wirethelaterfaultcanberemoved.Theloadshouldbekeptwithinratedlimitintheindustries.
Ina5kwinstallation,thefusecapacityiskepttobenearly5000/230=22amperes.Thefuse
wouldbekeptwithinratedlimit;but,ifafuseofhighcapacityisplacedinthecircuit,then,the
motorsetc.wouldrunoverloadedandsoontheywillgetspoiled.Thereforeitisadvisableto
runthemachine ontheirspecificloadvaluesonly.

54. 5.Earthing
Intheindustries,ifamotorisnotproperlyearthedanditsbodycomesincontactwithaphase
wire,thenitstartstogiveanelectricshock.Thefaultmayariseduetolossinsulationorbreak
inaphasewire.Fortesting,removetheearthconnectionofthemotor,connectatest-lamp
acrossthemotorbodyandearthpoint.Ifthetest-lampglowsthenthereisaearthingfault,in
themotor.Since,thefaultisdetected,thusitcanberemovedeasily.

55. Precaution–forusingmegger
(i)Beforetestingtheinsulationofaline,themainswitchmustbeswitchedoff.
(ii)Themeagermustnotbeusedonaliveline.
(iii)Theconnectingleadsofthemeagershouldnothaveanyleakage.
(iv) Themeagershouldbeplacedonahorizontalplane,anditshouldbeoperated
gentlyatastablespeed.
(v) Beforeactualinsulationtesting,checktheinstrumentthatitshouldindicate
zeroonjoiningitsLandEterminals.

56. (E)Use–Itisusedfor:
(i) Testingtheleakageofaninstallation
(ii) Testingtheshort-circuitofaninstallation.
(iii) Testingthecontinuityofaninstallation.
(iv) Testingtheproperearthling.
(v) Themeasurementofhighresistances.

57. WattageofLampforVariousUses
Thewattageofthelampsforvarioususesinabuildingaregiveninthe followingtable:
S.
No.
Place Lamp’s
Wattage
S.
No
Place Lamp’s
Wattage
1.
2.
3.
4.
5.
6.
7.
Drawingroom
Office
Diningroom
Bedroom
Dressingroom
Bathroom
Kitchen
60
60
25
40
40
25
60
8.
9.
10.
11.
12.
13.
14.
Staircase
Shop
Garage
Workshop
Playingroom
Stitchingroom
Readingroom
25
100
40
60
40
100
60