SERVICE MAINS.pdf

service mains

1. DEPARTMENTOFCOLEGEGATEANDTECHNICALEDUCATION.
BENGALORE
GOVERNMENTPOLYTECHNICRAICHUR
SUBJECT:ELECTRICALESTIMATIONANDCOSTING.CODE:15EE54T
UNIT-IISERVICEMAINS
1.Defineservicemains
Servicemainsistappingofelectricalenergyfromthesupplier’spoletoconsumers
premises.Oritisameansofprovidingelectricpowersupplyfromtheexistingpole
uptothemeterboard.
2.CodeofPracticeforservicemains
a)Servicelinefromoverheadlinesshouldbetappedonlyatthepointofsupport.
b)Overheadservicelinesshouldbewithin30mlengthandU.G.Serviceshouldbe
within60m.
c)Insulatedservicelineerectedotherthanacrossoralongstreetshouldnotbeless
than5.7mabovethegroundlevel,elsewhere4.3m.
d)Leadinpipesshouldbeusedforserviceconnection.
e)Themeterboardmustalwaysbeplacedattheentranceroomataheightof1.5
meter.
f)Themeterearthshouldnotbetappedforotherearthings.
g)Whenthetotalloadexceeds8KVA,evenforsinglephaseloads3phaseservice
connectionistobetakenandtheloadistobedistributedforallthe3phases.
h)E.L.C.B.(earthleakagecircuitbreaker)aretobeusedwhentheloadexceeds
5kVA.
3.Listthetypesofservicemains
Therearetwotypesofservicemains
a)Overheadserviceconnection
b)Undergroundserviceconnection

2. 4.ExplainOverHeadServiceMainswithdiagram
Thefigureshowstheoverheadserviceconnectionfortappinga3-phasepower
supply.Thetopmostwire(1)whichtakesmechanicalloadiscalledmessengerwire.
Thismessengerwireistiedtothesupportingpipe(4)inonesideandtothepole(6)
ontheotherside.Themessengerwireisbrokenatbothendsbymeansof1.1KV
breakinsulator(8).Tothismessengerwirereelinsulators(2)aresuspendedthrough
whichdoublesheathedPVCcables(3)aredrawn.Finallythecablesaretakentothe
meterboard(7)throughservicepipe(5).Theservicepipeisfixedtothesupportpipe
bymeansclamps.Ifthehorizontaldistancebetweenpoleandsupportpipeismore
than15meter,theninordertomaintainsupportpipeverticallyastayisrequiredto
thepipe(usuallycalledhalfpole).Whichistobebrokenatthemiddlebymeansof
1.1KVbreakinsulatoristobeprovided.Earthingistobeprovidedtothemeterwith
8SWGG.I.wire.
5.Listthematerials
a)Messengerwire
b)Reelinsulator
c)PVCcable
d)Supportingpipe
e)Servicepipe
f)Pole
g)Meterboard
h)Breakinsulator
6.Specificationofmaterialsusedoverheadservice.
a)Messengerwire:-10SWGG.Iwire
b)Supportpipe:-40mmdia.3mmthickG.Ipipe1.8mlongfor1-phaseor50mmdia.
3mmthickG.Ipipe1.8mlongfor3-phaseinstallation.
c)Servicepipe:-PVCpipe2mmthickofappropriatediameterdependingthesize
andnumberofcables.Usually2minlengthwith3numbersofbendsofthesame
dia.
d)Breakinsulator:-1.1KVporcelainbreakinsulator.

3. e)Servicecables:-2.5,4,6,10,------240sqmmdoublesheathedPVCaluminumcable.
f)Meterboard:-305x305x65mmfor1-phaseand500x500x65mmTWMBfor3-
phase.
g)Earthing:-G.I.pipe40mmdiameter,2.95mmthick,2.5mlong12.5mmholes
drilledatanintervalof300mm.thewholepitof340mmdiameteristobefilled
withcoalandsalt.
h)Earthwire:-8SWGG.Iwire
i)Fuseunit:-porcelainfuseunitofrequiredcurrentratingandvoltagegrade.
7.ExplainUGServiceMainswithdiagram
Generallytheundergroundcablesystemispreferredtothatofoverheadservice
system.ParticularlyincosmopolitancitieslikeBangalore,Mysore,Mangalore,Hubli
etc.TheUG-cablefrommeter-boardistakentogroundthroughGI-pipeusingbends.
Inthegroundusuallytrenchlayingisdoneincaseofnoobstruction.However,in
caseofroadcrossingetcinthegroundalsothecableistakenthroughGI-pipe.Using
tendsfromwhereitiswithPVCdoublesheathedcableswhichareflexible.Forsingle
phasetwincoreUG-cableisused.For3phaseseither4-croreor3andhalfcoreUG-
cableisused.AlwaysweareselectingsteelarmouredUG-cable.Thefixationofthese
steelarmouringinaconcentricwaywithouteffectinginsulationiscalledbonding.
8.Listthematerials
a)Undergroundcable
b)G.I.pipe
c)Pole
d)Pothead
e)PVCdoublesheathedcables
f)Meterboard

4. 9.SpecificationsofmaterialsusedinU.G.cable
a.Undergroundcable:
Sizeofcable:-Insq.mm.Suchas4,6,10,16,25,35,50,70,95,120,150,225etc
Conductormaterial:-Aliminiumonly(ACSR)
Noofcore:-2forsinglephase,3or3x1/2or4for3phase
Insulation:-PVCsheathedwithadditionalsheathingofeitherpaperinsulationor
leadalloy.
Voltagegrade:-1.1KVclassforlowandmediumvoltage.
Armouring:-Steelwirearmouredortapearmoured.
b.Pothead:
Voltagegrade:-1.1KVor11KV.
Material:-castiron.
c.Stonewarepipe:
Size:-101.6mmdia.
Length:-61m.
d.G.Ipipe:
Diameterofpipe:-40mmdia.for6,10and16sq.mmcablesor50mmdia.higher
size.
e.PVCCables:
Size:-insq.mmsuchas2.5,4,6,10,16,25etc.
Conductor:-Aluminium.
Insulation:-PVC
Voltagegrade:-250Vforsinglephaseor500Vfor3phase
f.MeterBoard:
300x300x65mm–forsinglephaseVTWB
500x500x65mm—for3phaseVTWB
g.Earthing:-40mmG.Ipipe3mmthick,2.5mlong,12.5mmholesdrilledatan
intervalof300mm.thewholepitof340mmdia.Istobefilledwithcoalandsalt.
10.Standardwiretable
Wiretableforcurrentratingforaluminiumcables.
Area(sq.mm) Singlecorecables(Amps)
1.5 10
2.5 15
4.0 20
6.0 27
10.0 34
16.0 43
25.0 59
35.0 69
50.0 91
70.0 134
95.0 153

5. voltage
11.Loadcalculationofoverheadservice,Sizeofwire,Typeofwire,
Protectivedevices
a.Loadcalculationofoverheadservice.
Totalload=Givenlightload+powerload
Loadcurrent=
lightload+powerload
voltage
b.Sizeofwire
Takefactorofsafety=2foroverheadand
=3forundergroundservice.
Totalcurrent=loadcurrentxfactorofsafety
Referringthewiretableasperthecurrentratingtoselectingthesizeofwire.
c.Typeofwire
1.PVCdoublesheathedaluminium250Vgcableforoverheadserviceand
2.PVCdoublesheathedaluminium250Vg2corefor1-phaseand3,3x1/2or
4 corethreephase500Vgundergroundservice.
d.Protectivedevices
Asperthetotalcurrentratingtoselectthefuseunit.
Eg:-totalloadcurrent=28amps.Thenfuseratingwillbe
30Aporcelainfuseunit250Vg.
Examples:ForSinglephase
1.prepareanestimateofcostforprovidingOverheadServicemainstofeedpower
supplytoanAEHinstallationhavingalightingloadof800Wandapowerloadof2.5
KW,foradistanceof10m.
Ans:-
1)Materialcalculation.
a)Loadcurrent=
lightload+powerload
=amps

6. loadcurrent=
800+2500
230
=14.35Amps
Factorofsafety=2
Loadcurrent=14.35x2=28.7amps.Say=29Amps.
Thesizeofthealuminiumcableis10sq.mm.
Lengthofeachlead=Poleside+Horizontal+Loose+meterside
=2+10+1+3=16m.
Thereforethetotallengthofcablerequired=16x2=32m.
b)38mmG.I.Pipe=1.8m.
c)No.breakinsulator=2
d)Noofreelinsulatoronelead=Horizontaldistance/0.75
=10/0.75=13.33say13N
Noofreelinsulatorfor2lead=13x2=26say2dozen
e)30mmPVCservicepipe=2m.
f)Nobendswithsamedia.=3Nos.
g)300x250x45VTWMeterboard=1No.
h)40mmG.I.Pipe2.5mforearthingand1kgof8SWGG.I.Wire.
i)15Afuseunits=2No
j)Massangingwire=1kg
k)Miscellaneousmaterials.
2)MATERIALREQUIREDFOR1-PHASEOVERHEADSERVICE
SL.No Pariculars Quantity
1 10sq.mmaluminiumdoublesheathedPVCcable250vg 32m
2 38mmG.I.pipe3mmthick1.8msupporting 1No
3 1.1KVporcelainbreakinsulator 2No
4 Porcelainreelinsulators15mmdia. 2dozen
5 30mmPVCpipe2mmthickforservicing 2m
6 PVCbendssuitablefor30mmpipe 3No
7 300x250x45mmVTWMeterboard 1No
8 40mmG.I.Pipe3mmthick 2.5m

7. 9 8SWGG.I.wireforearthing 1kg
1015Aporcelainfuseunit250Vg 2No
1110SWGG.I.formassanging 1kg
12Miscellaneousmaterials LS
3)CostofEstimation
Sl.NoPraticulars UnitQuantityRate
RsPs
Cost
RsPs
110sq.mmaluminiumdoublesheathed
PVCcable250vg
100M
(coil)
32 700.00224.00
238mmG.I.pipe3mmthick1.8m
supporting
M 1.8 120.00216.00
31.1KVporcelainbreakinsulator No 2 1.50 3.00
4Porcelainreelinsulators15mmdia Dozen 2 2.00 4.00
530mmPVCpipe2mmthickfor
servicing
M 2 10.00 20.00
6PVCbendssuitablefor30mmpipe No 3 2.00 6.00
7300x250x65mmVTWMeterboard No 1 200.00225.00
840mmG.I.Pipe3mmthickearthing M 2.5 100.00250.00
98SWGG.I.wireforearthing kg 1 32.00 32.00
1015Aporcelainfuseunit250Vg No 2 20.00 40.00
1110SWGG.I.formassanging kg 1 33.00 33.00
12Miscellaneousmaterialslikescrews,
gutties,rawlpugsandbituminous
compound.
LS 100.00
13Labourcharges
a)forservicingRs.120.00
b)earthworkRs.50.00
170.00
Total 1323.00
14Addcontingenciesandunforeseen
things@5%
66.15

8. Grand
Total
Say
1389.15
1400.00
(Estimatedrupeesonethousandfourhundredonly)
Examples:Forthreephase
2.Prepareanestimateforoverheadserviceconnectiontofeedpowersupplytoafactory
of15HP.Loadforadistanceof10m.
Ans:-
1)Materialcalculation
a)Approximatecurrent=1.6x15=24amps.
Factorofsafety=2
Loadcurrent=24x2=48amps.
Thesizeofthealuminiumcableis16sq.mm.
Lengthofeachlead=Poleside+Horizontal+Loose+meterside
=3+10+3+4=20m.
Thereforethetotallengthofcablerequired=20x4=80m.
a)50mmG.I.Pipe=1.8m.
b)No.breakinsulator=2
c)Noofreelinsulatoronelead=Horizontaldistance/0.75
=10/0.75=13.33say13N
Noofreelinsulatorfor4lead=13x4=52say5dozen
d)40mmPVCservicepipe=2m.
e)Nobendswithsamedia.=3Nos.
f)500x500x65VTWMeterboard=1No.

9. g)40mmG.I.Pipe2.5mforearthingand1kgof8SWGG.I.Wire.
h)30Afuseunits=3No
i)Massangingwire=1kg
j)Miscellaneousmaterials.
2)MATERIALREQUIREDFOR3PHASEOVERHEADSERVICE
SL.No Particulars Quantity
1 16sq.mmaluminiumdoublesheathedPVCcable500vg 80m
2 50mmG.I.pipe3mmthick1.8msupporting 1No
3 1.1KVporcelainbreakinsulator 2No
4 Porcelainreelinsulators15mmdia. 5dozen
5 40mmPVCpipe2mmthickforservicing 2m
6 PVCbendssuitablefor40mmpipe 3No
7 500x500x65mmVTWMeterboard 1No
8 40mmG.I.Pipe3mmthick 2.5m
9 8SWGG.I.wireforearthing 1kg
10 30Aporcelainfuseunit500Vg 3No
11 10SWGG.I.formassanging 1kg
12 Miscellaneousmaterials LS
3)CostofEstimation
Sl.No Praticulars UnitQuantityRate
RsPs
Cost
RsPs
116sq.mmaluminiumdoublesheathed
PVCcable500vg
100M
(coil)
80 900.00720.00
250mmG.I.pipe3mmthick1.8m
supporting
M 1.8 140.00252.00
31.1KVporcelainbreakinsulator No 2 1.50 3.00
4Porcelainreelinsulators15mmdia Dozen 5 2.00 10.00
540mmPVCpipe2mmthickforservicing M 2 10.00 20.00
6PVCbendssuitablefor30mmpipe No 3 2.00 6.00
7500x500x65mmVTWMeterboard No 1 225..00225.00
840mmG.I.Pipe3mmthickearthing M 2.5 100.00250.00

10. voltage
98SWGG.I.wireforearthing kg 1 32.00 32.00
1030Aporcelainfuseunit500Vg No 3 25.00 75.00
1110SWGG.I.formassanging kg 1 33.00 33.00
12Miscellaneousmaterialslikescrews,
gutties,rawlpugsandbituminous
compound.
LS 105.00
13Labourcharges
a)forservicingRs.120.00
b)earthworkRs.50.00
170.00
Total 1901.00
14Addcontingenciesandunforeseen
things@5%
95.05
GrandTotal 1996.05
Say 2000.00
(Rupeestwothousandonly)
Examples:ForsinglephaseUGSERVICE
3.prepareanestimateofcostforprovidingUGServicemainstofeedpowersupplyto
anAEHinstallationhavingalightingloadof800Wandapowerloadof2.5KW,fora
distanceof10m.
Ans:-
1)Materialcaculation
Given:
Lightingload=800W
Powerload=2.5KW
Distance=10m
Loadcurrent=
lightload+powerload
loadcurrent=
800+2500
230
=14.35amps.
Factorofsafety=3
Thereforeactualcurrent=loadcurrentxfactorofsafety
=14.35x3=43.05Amps
Sizeofcable=10Sq.mm,250Vgrade,doublesheathedPVCcable

11. a)Henceironpotof50A,2terminals,250Vgradeisrequired=1No.
b)LengthofGIpipe=3m(poleside)+2m(meterside)+2.5m(earthing)
=7.5m
c)No.ofGIbends=3Nos.
d)LengthofUGcable=10mhorizontal+1mlooseness+3mpoleside+2m
meter side
=16m.
Add10%forwastage=1.6+16=17.6say18m.
e)6sq.mmdoublesheathedPVCcable=12mforconnectiontooverheadline
f)Noofbricks
Sizeofbricks=11.5cmx23cmx7.5cm
No.ofbricks=
10x100
23
=43.47orsay45
g)Numberof15Afuseunits=2Nos.
h)300mmx300mmx45mmVTWB=1
i)ClampsforfixingGIpipewithpoleandmeterside=5
2)MaterialRequiredfor1-phaseUGservice
SL.No Pariculars Quantity
1 10sq.mmPVCUGcableAluminium2core1.1KVclass.GI
steeltapearmoured.250Vgrade.
18m
2 Bricks11.5cmx23cmx7.5cm 45No
3 38mmdiameter,3mmthickGIpipeforlayingcableand
earthing
7.5M
4 Ironpot50A,250Vgradewithtwoterminal 1No
5 PVCcable,6sq.mmdoublesheathed 12M
6 Procelainfuseunits15A,250Vgrade 2No
7 38mmdia,3mmthickGIbends 3No
8 300mmx300mmx45mmVTWB 1No
9 Earthingset 1No
10 ClampsforfixingGIpipewithpoleandmeterside 5No
3)CostofEstimation
Sl.No Praticulars UnitQuantityRate Cost

12. RsPs RsPs
110sq.mmPVCUGcableAluminium2core1.1
KVclass.GIsteeltapearmoured.250V
grade.
M 18 40.00/m720.00
2Bricks11.5cmx23cmx7.5cm No 45 5.00 225.00
338mmdiameter,3mmthickGIpipeforlaying
cableandearthing
M 7.5 165.00/m1237.50
4Ironpot50A,250Vgradewithtwoterminal No 1 168.00168.00
5PVCcable,6sq.mmdoublesheathed M 12 7.65/m 91.80
6Procelainfuseunits15A,250Vgrade No 2 40.00 80.00
738mmdia,3mmthickGIbends No 3 21.00 63.00
8300mmx300mmx45mmVTWB No 1 50.00 50.00
9Earthingset No 1 1200.001200.00
10ClampsforfixingGIpipewithpoleandmeter
side
No 5 18.00 90.00
11Miscellaneousmaterialslikescrews,gutties,
rawlpugsandbituminouscompound.
LS 50.00
Total 3975.30
[email protected]/m 18.00x10 180.00
Total 4155.30
13Add5%forcontingency,unforeseenand
variationonmaterialcostofRs.3975.00
198.75
GrandTotal
Say
4354.05
4400.00
(Rupeesfourthousandfourhundredonly)
Examples:ForthreephaseUGSERVICE
4).prepareanestimateofcostforprovidingUGServicemainstofeedpowersupplytoan
workshopof10HPloadforadistanceof10m.
Ans:-
1)Materialcaculation
Given:
Powerload=10HP
Distance=10m
a)Approximatecurrent=1.6x10=16amps.
Factorofsafety=3
Loadcurrent=16x3=48amps.
Sizeofcable=16sq.mm,500Vg,4coredoublesheathedPVCaluminumcable.

13. LengthofUGcable=10mhorizontal+1mlooseness+3mpoleside+2m
meter side
=16m.
Add10%forwastage=1.6+16=17.6say18m.
b)Henceironpotof50A,4terminals,500Vgradeisrequired=1No.
c)LengthofGIpipe=3m(poleside)+2m(meterside)+2.5m(earthing)
=7.5m
d)No.ofGIbends=3Nos.
e)16sq.mmdoublesheathedPVCcable=12mforconnectiontooverheadline
f)Noofbricks
Sizeofbricks=11.5cmx23cmx7.5cm
No.ofbricks=
10x100
23
=43.47orsay45
g)Numberof16Afuseunits=3Nos.
h)500mmx500mmx65mmVTWB=1
i)ClampsforfixingGIpipewithpoleandmeterside=5
2)MATERIALREQUIREDFOR3PHASEUGSERVICE
SL.No Pariculars Quantity
1 16sq.mmPVCUGcableAluminium4coreGIsteeltape
armoured.500Vgrade.
18m
2 Bricks11.5cmx23cmx7.5cm 45No
3 50mmdiameter,3mmthickGIpipeforlayingcableand
earthing
7.5M
4 Ironpot50A,500Vgradewith4terminal 1No
5 PVCcable,16sq.mmdoublesheathed 12M

14. 6 Procelainfuseunits15A,500Vgrade 3No
7 50mmdia.3mmthickGIbends 3No
8 500mmx500mmx65mmVTWB 1No
9 Earthingset 1No
10 ClampsforfixingGIpipewithpoleandmeterside 5No
3)CostofEstimation
Sl.No Praticulars UnitQuantityRate
RsPs
Cost
RsPs
116sq.mmPVCUGcableAluminium4coreGI
steeltapearmoured.500Vgrade.
M 18 80.00/m1440.00
2Bricks11.5cmx23cmx7.5cm No 45 5.00 225.00
350mmdiameter,3mmthickGIpipeforlaying
cableandearthing
m 7.5 200.00/m1500.00
4Ironpot50A,500Vgradewith4terminal No 1 225.00225.00
5PVCcable,16sq.mmdoublesheathed m 12 7.65/m 91.80
6Procelainfuseunits15A,500Vgrade No 3 40.00 120.00
750mmdia.3mmthickGIbends No 3 30.00 90.00
8500mmx500mmx65mmVTWB No 1 80.00 80.00
9Earthingset No 1 1200.001200.00
10ClampsforfixingGIpipewithpoleandmeter
side
No 5 18.00 90.00
11Miscellaneousmaterialslikescrews,gutties,
rawlpugsandbituminouscompound.
LS 100.00
Total 5161.80
[email protected]/m 18.00x30 540.00
Total 5701.80
13Add5%forcontingency,unforeseenand
variationonmaterialcostofRs.5701.80
285.09
GrandTotal
Say
5986.89
6000.00
(Estimatedrupeessixthousandonly)
TASK
1.PreparethescheduleofmaterialsforprovidingOHservice
connectiontoaresidentialbuildingwith1050Wlightingand
2.5KWheatingload.Thesupplierpoleis10m
away.Preparetheestimateofcost.
2.PreparethescheduleofmaterialsforprovidingUGservice
connectiontoaresidentialbuildingwith1KWlightingand
2.5KWheatingload.Thesupplierpoleis10m