Earthing system Of telecom equipment Chapter 1

Earthing system

1. For circulation to Trainees only 1
Earthing
D K Upadhyay
[email protected]

2. For circulation to Trainees only 2
•Question1.Why is Earthing of electrical apparatus
necessary?
•Ans:-The frame of every metal-cased electrical
equipment should be efficiently connected to earth, to
drain away any leakage of current due to poor
insulation, so that it may always be safe to work upon.

3. For circulation to Trainees only 3
•Question2.Explain why it is not safe to work on equipment
which is not earthed?
•neutral is Answer:-An a.c. sigle-phase,230 volt equipment fed from a
400 volts,3-phase,50 cycle system,whose solidly connected to earth.If
the insulation of the motor windings break down, current start leaking
in to the metal body of the apparatus which would get charged with
the supply pressure and become alive and dangerous,unless the
charge is drained away to earth by an earth connection.

4. For circulation to Trainees only 4
•When it is earthed, a fault in the winding would cause a heavy
current to flow in to the earth which would then blow out the fuse
on the phase line there by disconnecting the supply to the motor.
Earthing there fore, eliminates the possibility of any dangerous
potential on the body of the motor and also helps to ensure the
automatic clearing of the faulty equipment.

5. For circulation to Trainees only 5
•Question3.what is an earthing lead and what should be its
size?
•Answer:-The general rule is that the cross-section of the
earthing lead (Padarth ka aada Tircha Samkon me kataw)should be
at least half that of the main supply wire feeding the
installation.The size of the earthing lead should ,in any case
,be such that it shell never fuse out under the worst fault
condition

6. For circulation to Trainees only 6
•For large installation its cross-section should be not less
than 0.25 sq.inches for main connections, and
0.1sq.inches.for branch connection.

7. For circulation to Trainees only 7
Objective 0f Earthing
•Definition of Earthing .
•Purpose of Earthing .
•Requirement of effective Earthing.
•Class of Earthing.
•Material used in Earthing.
•Different types of earth electrode.

8. For circulation to Trainees only 8
EARTHING
Earthingisaeffectivemeasureofprotectionfrom
hazardouselectriccurrentwhichmayresulteither
duetopowerinduction,lightningorshortcircuit.
powerinduction:-Therearetwotypeofpower
induction.(a)MutualInduction.(b)SelfInduction.
(a)Mutualinduction:-
TransformerdsprimaryesaA.C.VoltagensrsgSa
blA.C.Voltagedsdkj.kSecondaryesaVoltage
generategksrkgSamutualinductiondsdkj.k

9. For circulation to Trainees only 9
(b)Selfinduction:-
EARTHING

10. For circulation to Trainees only 10
(i)ChokegenerateHighVoltagepulseto
ionisethegasinsideFL.
(ii)Limitsthecurrentwhentheconductionis
takenoverbygas.
Lighting:-Earthingprotecthumenlifeaswelas
building,equipmentetc.
Self induction

11. For circulation to Trainees only 11
Equipment'khVeSVydscusgksrsgSa'khVeSVy
fo|qrdslqpkydgksrsgS;fnQstbudslkFklEidZ
esavktk;srksekuodsfy,[krjkcutkrsgSaA;fn
equipmentdsckgjhHkkxdksvFkZdslkFktksM+
fn;ktk;rks'kkVZlfdZVdsdkj.kfo|qrvFkZesapyh
tk,sxhvkSjekuodkcpkogkstk,sxkAdjaVdk
izokg;fncircuitesayxsfusedhRatingT;knkgS
rksFusefi?kytk,sxkvkSjQstlslEidZVwVtk,sxk
vkSjequipment,oaekuodkcpkogkstk,sxkA
Short Circuiting

12. For circulation to Trainees only 12
Purpose of Earthing
(a)Toprotecthumanbeing.
(b)Reducecrosstalkandnoise:-
OnePoleofthebattery(+vepole)isearthedin
thetelephoneexchangesothatcrosstalkbetween
thevariouscircuitsduetothespeechcurrentofone
circuitfindingpaththroughtheotherviacommonbty
feedpointofthetransmissionbridgeandreduced
noiseviaearthedterminalofthebattery.

13. For circulation to Trainees only 13
ikojIykaV,oacSVjhds+iveVjehuydksvFkZds
lkFktksM+nsrsgSaAØklVkdlsmRiUugqvk
djaVvFkZesapyktkrkgSAftllsØklVkdlqukbZ
ughansrhA
(b)Protectionofcostlyapparatusand
personsagainstforeignvoltageandleakage
currentfrompowerwiringtothemetallicframe
oftheequipmentfdlhHkhotglsleakagedjaV
dsdkj.kequipmentdkssafedjrkgSaA
Purpose of Earthing

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(e)Protectionofbuildingsandequipmentsfrom
lightningstrikesExchangebuildingdkslightning
strikelslqj{kkiznkudjrkgSaA
(f)Earthisusedtoaffordconvenienceand
reliabilityintheswitchingapparatusoftelecom
circuits.fLofpax;a=kesami;ksxfd,tkrsgSamuesa
ONandOFFgksuslstksCurrentiSnkgksrkgSog
djaVO;o/kkumRiUuughadjrktcSystemdks
Properlyearthfd;ktkrkgSA
(g)Earthinginpowersupplysystemisusedto
effectreliabilityofpowerasithelptoprovide
stabilityofvoltagecondition.Properearthinggksus
lsVoltagelossughagksrkgSaA
Purpose of Earthing

15. For circulation to Trainees only 15
ClassofEarthingSystems
EarthingsystemsareProvidedtoservemany
differentpurposes.Theymaybedividedintotwo
majorcategories.
(a)ServiceEarthingsysteme.g.
(i)Switchingequipmentearth
(ii)Transmissionequipmentearth

16. For circulation to Trainees only 16
(iii)Measuringequipmentearth
(iv)A.C.Powersupplyearth
(v)Miscellaneousequipment earth(e.g.
Telegraphs)
(b)ProtectiveEarthingSysteme.g.
(i)Powersystemearthtoprovideprotection
againstexcessivecurrent.
Class of Earthing Systems

17. For circulation to Trainees only 17
(ii)Lightningprotectiveearthtoprovide
protectionagainstexcessivevoltage.
(a)Serviceearth-bldsvUrxZrtujsfVaxLVs'ku
lstksykbZuvkrhgSmllsconnectedequipment
vkrsgSaA
(b)Protectiveearthingsystem-forprotection
againstshortcircuitingvFkZfiVlsequipmentrd
vkusokykdUMDVjgSohxstdkgksaukpkfg,tks
ThousandofAmpCurrentviusvUnjlsizokfgr
Class of Earthing Systems

18. For circulation to Trainees only 18
ServiceearthingsystemshouldhavealowDC
resistancetothegeneralbodytotheearthin
ordertoensurethatthepotentialdropacrossthe
earthconnectionislow.Ifanycurrentflows
throughtheserviceearthingsystemapotential
differencewillbedevelopedacrosstheearth
connection.
RequirementofServiceEarthingSystem

19. For circulation to Trainees only 19
RequirementofprotectiveEarthingsystem
(a)Carrytheanticipatedvalueofovercurrent
withoutoverheatingandwithoutburningout;fn
gekjkikojIykaV2200AmpdkgSrksvFkZfiVlsikoj
IykaVrdtksdUMDVjvkrkgSmldh{kerkbruhgksuh
pkfg,fd;fn2200,fEi;jlsT;knkdjaVHkhgksrksmls
vFkZesaikldjnsfcukxeZgq,;kfcuktysA
(b)EnableSufficientCurrenttoflowtogroundto
ensurethatanyovercurrentprotectivedevice(e.g.
FuseCircuitbreakeretc.)willoperatetodisconnect
thecurrentafteraveryshorttime.

20. For circulation to Trainees only 20
dUMDVjtksvFkZfiVlssystemrdvkrkgSdh{kerk
bruhgksuhpkfg,rkfdogfcukMeltgq,T;knkdjaV
vius}kjktehuesaHkstldsAsystemdslkFk
connectedprotectivedevicestSlsfuse,circuit
breaker,T;knkdjaVdsizokglsDisconnectgksdj
systemdkssafedjldsaA
Requirement of protective Earthing system

21. For circulation to Trainees only 21
(c)Theresistanceoftheearthconnection
mustremainreasonableconstantthrough
outthevariousseasonsoftheyearItshould
bereasonablyconstanti.e..5,.8,not4
or5vFkZdkjftLVSalgjsdekSleesa,dlk
jgukpkfg;s¼o"kZdsgjsdekSleesa½vFkZ
dkjftLVSal.5;k.8gksukpkfg;s4;k5
ughaA
Requirement of protective Earthing system

22. For circulation to Trainees only 22
(d)Earthwhichprotectagainstexcessivevoltage
e.g.earthconnectedtolightningprotectionsystem.
Mustpossessalowsurzeimpedenceinorderto
enablethelightningsurzecurrenttobeeasily
conveyedtotheearthandthusdivertedawayfrom
theequipmentwhichistobeprotectedfromthe
lightningtksVoltagerfM++rlsvkjgkgSmldkSurze
impedence(z)degksukpkfg,rHkhogequipmentdks
cpkdjtehuesapyktk,sxkltZvjSLVjdsek/;elsAltZ
vjSLVjlowimpedancetypetappeddevicegSblesaxSl
gksrhgSHighVoltageblesalsiklgkstk;sxkflLVelsQ
jgsxkA
Requirement of protective Earthing system

23. For circulation to Trainees only 23
Attemptstoprovideseparateearthingsystemfor
differentpurposesatacommonlocationhavegenerally
provedtobeunsatisfactoryforthefollowingreasons
(a)Inpracticeitisusuallynotpossibletoensurethat
thereisnoelectricalcouplingbetweenseparateearthing
systemsincloseproximity.Thisisbecauseofcasual
anduncontrolledinterconnectionwithintheinstallation
andalsobecauseofgalvaniccouplingintheground.
(b)There is a risk of fire and a risk of danger to
human life because a difference in potential between
various earths might cause excessive current and/or
excessive voltage.
Separate Earths Vs. Common Earth

24. For circulation to Trainees only 24
(c)Currentmayflowthroughthestructureor
betweenvariousearthingsystemsandcause
corrosion.vyx&vyxvFkZfuEudkj.kksalslarks"kizn
ughagksrkgSA;fnDifferentequipdsfy,Different
eqrthingsystemgksaxsrksogvkilesacouplegks
tk,saxsAvFkZfiVdhxgjkbZesavUrjgksausdsdkj.k
mldkpotentialdifferenceHkh,dlkughagksxkftldkj.k
'kkdyxldrkgS]vkxHkhyxldrhgSlkFkghlkFkvFkZ
dUMDVjvkSjstructureofearthingHkhcorrdedgksxk
AbUghmijksDrdkj.kksalscommonearthnhtkrhgS
;gghpyuesagSrFkkcommonearthghlkjh
vko';drkvksadksiwjkdjrkgSAT;knkvFkZjftLVSalokyk
vFkZsystemykbZVfuaxdsfy,tksM+ktkldrkgStks
HkoudslehigksAdejftLVSalokykelectrodetksHkou
lsnwjgSmldksHkhblelectrodelstksM+djproper
Separate Earths Vs. Common Earth

25. For circulation to Trainees only 25
MainAdvantageofaCommonEarthingSystem
(a)ByCarefullybondingthevariousearthingsystems
together.Thepotentialdifferencebetweenoneearth
connectionandanotherisnegligible.Thusnoexcessive
Currentorvoltagewillbedevelopedwithintheearthing
system.
(b)Ifduetoexcessivevoltageorcurrenttheprotective
earthrisesthensowillallotherearthriseinpotential
thusonceagainpreventingthedevelopmentofpotential
differencewithintheearthedenvironmentofthe
installationvyx&vyxLFkkuksaesayxk;sx,rhu;kpkj
bysDVªksMksadksvkilesatksM+usijVksVyjftLVSalde
gkstkrkgS,oaiksVSfU'k;yfMQjSaldelsdegkstkrkgSA
vyx&vyxvFkZdsdkja.kmRiUucurrentvkSjVoltage
systemdksuqdlkuigaqpkldrsgSadkeuvkfFkZxdsdkj.k
geuqdlkulscpldrsgSaA

26. For circulation to Trainees only 26
Earthingsystemsshouldbedesignedtoachive
thefollowing
(a)AdequateCurrentcarryingcapacity
(b)Adequatemechanicalstrengthtowithstandthe
rigours(l[r)ofservicewithoutfracturing.
(c)Inthecaseoflightningprotectiveearths
adequate-surge-currentcarryingability.
(a)vFkZsystemblrjgdkgksukpkfg,tksvius}kjk
overcurrentdksvklkuhlsizokfgrdjlds(b)vFkZ
systembruk'kfDr'kkyhgksukpkfg,tksjkstejkZds
izHkkoksadks>syldsA(c)Earthelecrode dkQh
etcwrgksukpkfg,tkslightningstrokedkHeavy
voltagelgldsA
DesignPrinciplesofEarthingsystems

27. For circulation to Trainees only 27
EarthingSystemDesigns
Itisnotappropriatetospecifyortorecommendthedesignsor
dimensionsofearthingsystemwhicharetobeprovidedfor
variouspurposes.Itisappropriate,howevertodrawattentionto
theprincipleembodiedingooddesignandthishasbeendone[kkl
designdkmldsvkdkjizdkjdko.kZudjukmfprughagSAt:jh;sgS
vkfFkZxdsfl)karksadsvPNhrjgle>ukrkfdgevPNhvFkZcukdj
vko';drkdksiwjkdjldsaA
Lightningprotectionearth-
TheDcresistanceofsuchanearthbeofnotmorethansome
specified(low)value.TheneedforachievingalowDcresistance
isnowbeingquestioned.Itisimportantthatalightingearth
electrodesystemby:
(a)Ascloseaspracticabletotheplantorequipmenttobe
protected.
(b)Connectedtotheprotectorsviaconductorshavingminimum
surgeimpedance(i.e.nosharpbendsorcoildintheconductor)

28. For circulation to Trainees only 28
(c)Connectedtothatplantvialightingprotectorsof
adequatecurrentcarryingcapacityandan
appropriatevalueofbreakdownvolotageLDCvFkZ
dsfy,vFkZjftLVSaldhvaluedelsdegksaukpkfg,A
fdarqtgkalightningprotectiondhckrvkrhgS,oatgka
feV~VhdhresistivityT;knkgSogkalightning
protectionT;knkegRoiw.kZgSAvr%ltZImpedance(z)
degksaukpkfg,bldsfy,vFkZogh;kdUMDVjtksvFkZ
fiVlsykjgsgSa,oatksdUMoVjlightningArresterlsyk
jgsgSamlesasharpbendughagksaukpkfg,]vkfFkZx
dsfy,,dElectrodeuysdjlekuyEckbZdspkjElectrode
tksvkilesaRightAngleesagksrksbudkfeyktqyk
ImpedencedegkstkrkgSaA
ElectricalImpedanceZ=R+JxwhereR=Resistance
andJ=-1
Earthing System Designs

29. For circulation to Trainees only 29
ServiceEarth
ServiceearthwhichcarryCurrent(e.g.teleprinter
earthwhichmaycarry20-25mA)mustbecapableof
servivingthedischargeofsuchcurrenttogroundfor
theirdesignedworkinglife.Itisofinteresttonote
thatadirectcurrentof1Ampflowingthroughasteel
earthelectrodewillconsumeapproximately10kgof
steelperannum.Thusifanearthelectrodeisto
carry25mAfor20yearsitmustcontaininaccessof
5kgsteel.Inordertoensurethattheelectrodeis
stillinworkingorderafterthisperiodafactorof
safetyoftwowouldmeanthattheearthelectrode
mustcontainatleast10kgofsteel.

30. For circulation to Trainees only 30
TeleprintertksexchesayxkgqvkgSmldsEarthelectrodels;fn20-25mA
CurrentflowgksrkjgrkgSrks20lkyesa5Kgsteel[kRegksxkA
\1Amp-10kgsteel1lkyesaConsumegksrkgS(or1000mA)
gksrkgS
(a)\100ma- 10kgx100
……………… =1kg
1000
100mAcurrentdsfy,1kgsteel
(b)\25mAcurrent-10kgx25
…………… =1/4kg/year
1000
100mAcurrentdsfy,1kgsteel
(c) rks20 lkyesasteel yxsxk1/4x20 = 5 kg steel ;fn 20 lkyrd vFkZBhd
j[kukgksrks5 kg steel vf/kdyxsxkvr% steel electrode esa10 kg steel yxkuk
gksxkA

31. For circulation to Trainees only 31
Earthelectrodematerial
CopperisagoodConductorofelectricityisCorrodedeasilyso
thatitshouldnotbeusedyoushouldcareforthat.Itisbetter
tousedGalvanizedsteel,Plainsteel,stainlesssteeletc.for
earthelectrode.
Requirementoftheearthingsystemintelephone
Exchange-
(a)Toprovidealowresistancepathtoground.
(b)Tobeabletodischargethatmaximumanticipated
currentwhichtheearthsystemisexpectedtocarrybothunder
workingconditionsandunderfaultcondition.
(a)yksResistanceikFkgecuk,saxsrksfaultConditionesatks
HeavyCurrentelectrodeds}kjkiklgksxktehuesatkusdsfy,
ogurksvFkZelectrodedksxeZdjsxkvkSjugh{kfr
igaqpk,sxkA

32. For circulation to Trainees only 32
(b)NegativelsequipmentdkssupplynhtkrhgS
PositivePoledksgrounddjnsrsgSArksikFk
NegativetogroungdschpcujgkgSANormal
CoditionesacurrentdksikldjsxkghlkFkghlkFk
faultConditionesatksabnormalcurrentdevelop
gksxkmlsHkhvkfFkZxsystemdksvius}kjkikldjus
dh{kerkgksauhpkfg,A
Earthelectrode:-Fourtypeofearthelectrodes
arecommonlyusedforEarthingsystem
1.Rodelectrode
2.Plateelectrode
3.Stripelectrode
4.Ring electrode

33. For circulation to Trainees only 33
S SpikeEarth(RodElectrode)
Thepresentarrangementofearth
electrodesystemconsistsoftwentynumbers
of25.0mmor38.0mmdia.GIpipes,eachof
275cmor375cmlength.Eachpipeisused
asearthspikeandissodrivenintotheground
thatitstopremainsatsomedepthbelowthe
groundsurface.Thespacingbetweenanytwo
spikesshouldnotbelessthan375cm
ordinarilyInnocase,itshouldbelessthan
250cm.AtypicallayoutisshowninFigure4.

34. For circulation to Trainees only 34
The positions of the spikes should be marked out on
the site and a trench no wider than necessary
should be excavated. The trench should be 70 to
100 cms deep. The spike should be driven vertically
into the trench until the top of the driving head is 30
cms above the bottom of the excavation. Spikes can
be driven in quite easily with a sledge hammer for
round electrodes. A new arrangement has been
developed consisting of a sliding hammer placed on
the electrode so that the work may be carried out at
a level convenient to the workman without a ladder
or auxiliary platform. The blows are delivered to the
Spike Earth(Rod Electrode)

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36. For circulation to Trainees only 36
rodatapointneartotheground.Thedrivingheador
asuitableboltissuppliedwitheachearthspikeand
thismustbeusedtopreventthetopofthespikebeing
damagedduringthedrivingoperation,whenthespike
hasbeendrivenfullyintotheground,itwillprobably
befoundthatthedrivingheadwillbetightfitonthe
spikeandinthesecircumstancesitmaybeleftin
position.

37. For circulation to Trainees only 37
Incaseofnewbuildingringearthshouldact
astheequipotentialbondingandallearthing
equipmentsaretobeextendedfromthering
earth.
Whereitisdifficulttolayringearthsuchas
private/rentedbuildingduetospaceconstraints,
theplate/spikeearthmaybesuited.The
constructionpracticeofplateearthisasfollows.
PlateEarth:
Thearrangementofconstructionofplateearthing
isshowninFigure-3.

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39. For circulation to Trainees only 39
Thisconsistsofabadstrip1mmwideand6gms/square
cmburiedatadepthoffrom60to90cms.Theshouldbe
preferablylaidononecontinuouslengthof2450cms.
Otherwisetwolengthsof1225cmshouldbelaidatleast
250smapartandoverlappedbyatleast125mm,thetwo
electrodebeingparallelattheM.D.F.earthbar.Theearth
leadprotectedbyaloadpipeasdescribedinspikeearth
electrodesystemshouldbeconnectedtotheleadstripfor
atleast125mmbyaplumberiswipedjointasshownin
thediagrambelow.
LeadStripElectrodeSystem

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Lead Strip Electrode System

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Allexposedsurfaceofthetinnedcopperwireandthe
adjacentleadsurfaceshouldbeliberallycoatedwithblack
paintsuitableforironwork.
Earthplateelectrodesystem
Thisconsistsoffourgalvanizedironplatesof145
SWG76cmssquarearrangedasshowninthediagram
below
Thesefourplatesareplacedverticallyandatdiagonally
oppositeinanexcavation185cmsquareandofadepth
sufficienttoreachdampsoil.Thedepthshouldneverbe
lessthatabout250cmsandneednotbegreatherthan500
cms.Theleadpipecarryingthemainearthleadshouldbe
asclosetothetailsoftheplatesaspossible.

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43. For circulation to Trainees only 43
Spikeearthelectrodesystem:Thissystemis
generallyusedatallnew auto exchange
installationswhereadequatespaceisavailable
aroundtheexchangebuildingandwheresubsoil
suitablefordrivinginpipestotheprescribed
depthexist.
Leadstripelectrodesystems.Thisisusedwhen
adequatespacearoundtheexchangebuildingis
availablebutwhererockisencounteredatadepth
lessthan375cmbelowgroundlevel.
Conditiondeterminingthetypeof earthelectrode
systemtobeused

44. For circulation to Trainees only 44
Earthplateelectrodesystem:Thisisemployed
whenthelayoutoftheexchangesiteissuchthat
adequatespaceisnotavailableto installan
earthelectrodesystemoftypes(a)and(b)
mentionedabove.
Locationoftheearthelectrodesystem
Inmostcasesitispossibletoprovidetheearth
electrodesystemonthespacearoundthetelephone
exchangebuilding.Thefollowingpointsneedcareful
attentionbeforechoosingthesitefortheearth
electrodes.
Conditiondeterminingthetypeof earthelectrode
systemtobeused

45. For circulation to Trainees only 45
Theelectrodesmustbelocatedinundisturbed
soili.e.;notinmadeupsoilorloosesoilorrubble.
Ifnewbuildingsorextensionstoexistingbuilding
aretobeerectedonthesite,theareatobe
coveredbythesemustbeavoided.
Locationoftheearthelectrodesystem

46. For circulation to Trainees only 46
Theelectrodesshouldnotbeburiedinaposition
wheredamageislikelytoresultfromheavyvehicular
trafficnearby.
The position chosen for the electrodes should be
such as to give the shortest and meet direct run
practicable to the cable chamber, or to M.D.F.
where cable chamber does not exist.
Locationoftheearthelectrodesystem

47. For circulation to Trainees only 47
Asfaraspracticable,theelectrodesshouldbe
placedatleast185cm fromtheintendedor
probablepositionofundergroundmetalpipesor
cablebelongingtootherundertakingtoreduce
riskofdamage.
Itshould,asfaraspossible,befarremovedfrom
othersimilarearthinarealikeAC,earthetc.andin
nocaseshouldtheseparationbetweenthetwobe
lessthan375cms.
Locationoftheearthelectrodesystem

48. For circulation to Trainees only 48
After the electrodes have been located properly bent
and covered over, suitable visible markers should be
laid over the electrodes for future identification. A
route map for the bonding wire should be drawn up
and displayed in the M.D.F. room. Copies should be
made available to the authorities responsible for
planning the building operation in the premises.
Locationoftheearthelectrodesystem

49. For circulation to Trainees only 49
Inalltransmissionandswitchingsystems,a
combinedringearthshouldbeprovided.The
installationprocedureisdescribedbelow.
LayingofRingEartharoundNewTelecom
DepartmentalBuilding:
INSTALLATIONOfRingEarth

50. For circulation to Trainees only 50
TheringeartharoundtheTelecombuildingand
towerisshowninFigure1.Atrench,30cms,wide
andnormally150cms,deepisdug.Thedepth
shouldnotbelessthan60cms.Inanycase.AGI
(GalvanizedIron)stripof50x3mm.Islaidinthe
trench.Thetrenchshouldbeminimumonemeter
awayfromthebuilding.Inthecaseofblackcotton
soil,thetrenchshouldbesufficientlydeeptoavoid
crackingofsoilinsummer.
INSTALLATIONOfRingEarth

51. For circulation to Trainees only 51
Incaseorrockyorhardmurramsoil,thedepth
maybe60to90cms.Incaseofrocky,hard
murramandblackcottonsoil,thetrenchshould
notbefilledbytheexcavatedmaterialandinstead
foreigngoodearth,i.e.yellowsoilorash,which
arefineandcohesiveinnature,shouldbeused.
INSTALLATIONOfRingEarth

52. For circulation to Trainees only 52
TheG.I.stripsaretobeconnectedwitheach
otherasshownin Figure2.Thejointsaretobe
properlywrappedandsealedbywaterprooftape
toavoidany
While filling the trench, the earth may be rammed in
layers, so as to give cohesiveness and compactness
to the soil.
INSTALLATIONOfRingEarth

53. For circulation to Trainees only 53
INSTALLATIONOfRingEarth

54. For circulation to Trainees only 54
Ingress of moisture at the joint, while laying the Gl
strips for ring earth, it should not be bent sharply at
right angles, but laid in smooth curve of not less than
one metre radius.
INSTALLATIONOfRingEarth

55. For circulation to Trainees only 55
Forthepurposeofmeasurementofearth
resistance,smallinterconnectingstripshould
beprovidedintheringearthinasmall
manholechamber,sothatringearthcanbe
brokenfromloop.
Incaseofringearth,earthresistanceisnota
majorsignificantitemwhereallequipmentis
earthedtoacommonring.Fortestingofearth
resistancevalueofcommonedearth(by
commoningofno.ofindividualearth),the
MEASUREMENT OF EARTH RESISTANCE AND IT’S LIMIT

56. For circulation to Trainees only 56
testingofindividualearthistobedoneby
disconnectingitfromEquipotentialbonding.
Theearthresistanceshouldbelessthanor
equalto0.5ohmforindividualearthconnected
toEquipotentialbonidng.Inonlyexceptional
cases,earthresistanceisallowedupto1.0
ohms.Formeasurementofearthresistance
pleaserefertoElNo.G.0002,Issue1,date–
15.09.1966.
MEASUREMENT OF EARTH RESISTANCE AND IT’S LIMIT

57. For circulation to Trainees only 57

58. For circulation to Trainees only 58
i.G.I.stripsofsize50x3mm.Arelaidinaring
trenchandconnectedtotowerlegs,earthbar
inpowerroomandengineroom.Etc.Alljoints
insidetheearthshouldbemadewaterproof.
ii.Towerandotherconnection:Eachlegis
connecttoringearthbymeansofGIstrip.All
connectionsaremadebyGLnutsandboltsfor
GltoGlwithaleadstripof1to3mmthickin
betweenforensuringpropersurfacecontact.
Thatis,
MATERIALUSEDINEARTHING

59. For circulation to Trainees only 59
(a)Glstripto……GlstripByGlnutsandbolts
withleadstrip1to3mm.Thickinbetween.
b)Glstripto……CopperstripConnectedbybrass
nutsorlug,anandboltscoveredtomakeit
moistureproof.
c)Copperto….copperstripWithinsulationtape&
orlugsshouldbewatertightoutsidethe
building
.
MATERIALUSEDINEARTHING

60. For circulation to Trainees only 60
d)Connection……insidethe19x6mm.Copperstrip
isbuildingused
IMPORTANTPOINTSFORCONSIDERATION IN
EARTHING:
(i)Chemicaltreatmentofearthusingsalts,etc.are
notrecommendedasthechemicaltreatment
doesnotlastlongandneedstobechecked
periodically
MATERIALUSEDINEARTHING

61. For circulation to Trainees only 61
(ii)AseparateGlstrip50x3mmisusedtoconnectthe
lightningspiketoringearthtoensureproperconnectivity
oflightningspikewiththeringearthasshowninFigure
13.
(iii)Earthconductorshouldnotbeencircledwithmetal
clampswhile takingitalongthewall.Thisisessential
toeliminatethehigh inductivereactancethatwill
impedetheflowofsurgecurrentalongtheconductorin
caseoflightening.
(iv)Earthingconductorsshouldnotpassthroughanymetallic
conduitorpipeasthiswillincreasesurgeimpedance.
IMPORTANTPOINTSFORCONSIDERATION INEARTHING:

62. For circulation to Trainees only 62
(v)Thereshouldbenosharpbendsalongtheentirelengthof
earthconductors.Bendingshouldbedonewitharadiusof
onemetre.
(vi)Indigitalsystems,equipmentscontainactivedevicessuch
asFET,MOSandCMOSwhicharestatic-sensitivecomponent
andcanbe permanentlydamagedifitcomesincontact
withhumanbody possessingelectrostaticpotential.As
suchantistaticfloortilesormatsshouldbeinstalledand
connectedtoearth.Ifantistaticflooringisnotprovided,a
antistaticwrist-strapwhichisproperlyearthedshouldbeused
whileworkingonsuchequipments.
IMPORTANTPOINTSFORCONSIDERATION INEARTHING:

63. For circulation to Trainees only 63
(vii)Allthejointsofthesimilarmetalsshouldbe
waterproof.
Reference:
1.CCIR
2.APOEIonRadioTelevision,PL1000
3.EIof“MeasurementofExchangeEarthwithan
EarthMeggar”ElNo.G.0002,Issue1,dated
15.09.1963.

64. For circulation to Trainees only 64
4.ITU-T recommendation K.27 “Bonding
ConfigurationsandEarthinginsidea
TelecommunicationBuilding”.
5.TransmissionMaintenanceHand/book.
6.ElectricalEarthing&AccidentPreventicbyM.G.
Say.
7.LightningProtectionforElectricalSystem(Beck).
8.EarthingTelecommunicationCCITT1976.
Reference:

65. For circulation to Trainees only 65
9.TechnicaldescriptionofRadioRelayeqpt.
GYPES GIT-4000/800&6000/1800
(Budapest).
10.ElectricalTransmission&Distribution
referencebook.
11.TheEarthingProblemparticularlyinits
applicationtoTelephony(MartinThialets).
Reference:

66. For circulation to Trainees only 66
12.TheProtectionofTransmissionSystemsagainst
Lightning(Lewis).
13.SouthAfricanInstituteofElectricalEngineersJune
1955.
14.TheprotectionofTelecommunicationlines&
EquipmentagainstlightningDischargesCCITT
1974.
Reference:

67. For circulation to Trainees only 67