Meaning of service mains, code of Practice for service mains, types of service mains- Over Head Service Mains -materials and specifications, UG Service Mains -materials and specifications, Standard wire size table, current ratings for Aluminium, copper conductors and selection of size of conduit pipe as per the size and number of wires. Load calculation, selection of size and type of conductor/UG cable, discrimination of size of protective devices, Quantity calculation, schedules of materials and estimates for single phase OH service connection, three phase OH service connection, single phase UG service connection and three phase UG service connection.

1. 1
Prepared By:
Mr.Premanand Desai L/EE
B.L.D.E.A’s SHREE SANGANABASAVA
MAHA SWAMIJI POLYTECHNIC,
VIJAYAPUR-03
E-mail ID:ssmp.premananddesai@bldea.org
cell no : +91 7892881829
COURSE & CODE : ELECTRICAL ESTIMATION AND COSTING (15EE54T)
UNIT - 02
SERVICE MAINS

2. 2
COURSE & CODE : ELECTRICAL ESTIMATION AND COSTING (15EE54T)
UNIT - 02
SERVICE MAINS
2.0 Service mains
The overhead line or cable connecting the suppliers distributing line to the consumers premises
is called service main or service line or service connection.
Types of Service mains -
1. Overhead service.
2. Underground (UG) service
2.1 Code of Practice for service mains
1. Service Line from Overhead lines should be tapped only at the point of support.
2. Overhead service line should within 30 Meters length and UG service lines should be
within 60 Meters.
3. Insulated service line erected across or along street should not be less than 5.7Meter
above the ground level, elsewhere 4.3Meter.
4. Lead-in-pipes should be used for service connection at building side.
5. The meter board must always be placed at the entrance room at a height of 1.5 to 2
meter.
6. The meter earth should not be tapped for other earthing’s.
7. When the Total load exceeds 8KW, even for single phase load, then 3-Phase service
connection is to be taken and the load is to be distributed for all the 3-Phases equally.
8. E.L.C.B (Earth Leakage Circuit Breaker) are to used when the load exceeds 5KW.
2.2 Over Head Service Mains
•
1. G.I Top most wire (Messenger wire)
2. Reel Insulators.
3. PVC Cables (Double Insulated)
4. G.I Supporting Pipe
5. Service Pipe.
6. Pole
7. Meter board
8. Break insulator (1.1KV)

3. 3
The Figure shows the overhead service connection for tapping a 1-Ø or 3-Ø power supply. The
top most wire (1) which takes mechanical load is called messenger wire. This messenger wire is
tied to the supporting pipe(4) in one side and to the pole (6) on the other side . The messenger
wire is broken at both ends by means of 1.1KV break insulator(8). To this messenger wire reel
insulator (2) are suspended through which double sheathed PVC cables (3) are drawn. Finally the
cables are taken to the meter board(7) through service pipe(5).
The service pipe is fixed to the support pipe by means of clamps. If the horizontal distance
between pole and support pipe is more than 15Meter, then in order to maintain support pipe
vertically a stay is required to the pipe (Usually called half pole ) which is to be broken at the
middle by means of 1.1KV Break insulator is to be provided. Earthing is to be provided to the
meter with 8 SWG G.I wire.
2.2.1 Materials and specification of Over Head Service Mains
Sl. No Name of the material Specification
1. Messenger wire 10 SWG G.I wire
2. Support pipe 40mm diameter 2.95mm thick G.I pipe 1.8meter long for single
phase or 50mm diameter and 2.95mm thick G.I pipe 1.8meter
long for 3Phase installation.
3. Service Pipe PVC pipe 2mm thick of appropriate diameter depending on the
size and the number of cable to be taken by the pipe. Usually
2meter in length with 3 Number of bends of the same diameter.
4. Break Insulator 1.1KV porcelain break insulator.
5. Service Cable Double Sheathed PVC Aluminum cable of appropriate square mm
cross section depending on the load and 250V grade (1-phase) &
500V (3-Phase) Standard cross section of Aluminum in Sq.mm are
2.5, 4 , 6 , 10 , 16 , 25 ,35 , 50 , 70, 95 , 120 , 150 , 185 and 240 in
the cables.
6. Meter Board For single Phase power connection teak wood back covered meter
305×305×65mm made out of 15mm thick plank for front and
12mm plank for the back with 40 × 20 mm batten around (Using)
fixing screws in back and front
7. Earthing 40mm Diameter G.I pipe 2.95mm thick, 2.5Meter long 12.5mm
Holes drilled at an interval of 300mm. The Whole pit of 340mm
diameter is to be filled with coal and salt.
8. Earth wire It is 8 SWG G.I wire for Connecting meter body to earth pipe.
9. Fuse Unit Porcelain fuse unit of required current rating and Voltage grade.

4. 4
2.3 Underground (U.G) Service Mains
Generally the Under Ground cable system is preferred in Thickly Populated areas Or Cities like
Metropolitan Bangalore , Mysore , Chennai , Delhi etc.
The U.G Cable(1) from the meter board (6) is taken to ground through G.I Pipe using bends. In
the ground usually trench laying ,In case of road crossing etc cable is taken through G.I pipe(2)
using bends from where it is connected pot head(4) of suitable current range. After this pot head,
the supply is linked to the line with P.V.C double sheathed cable(5) which are flexible. For a single
phase twin core UG cable & For 3-phase, 4-core or 3-core & half core UG cable is used. Always
steel armoured UG cable.
2.3.1 Materials and specification of Under Ground (U.G) Service Mains
Sl. No Name of the material Specification
1. Underground cable In Square mm such as 4,6,10,16,25,35,50,70,95,120,150,225 etc.,
Aluminium Conductor material , PVC Sheathed insulated, steel
armoured, 1.1KV class, For a 1-Ø twin core UG cable & For 3-Ø - 4-
core or 3-core & half core
2. Pot Head Cast Iron Material , 1.1KV or 11KV grade
3. G . I pipe 40mm diameter or 50mm diameter for higher sizes.
4. PVC cable Aluminium, 2.5, 4 , 6 , 16 , 25 sq.mm
5. Meter Board 300×300×65 mm box Teak Wood Varnished Board – For 1-Ø Supply
500×500×65 mm box Teak Wood Varnished Board – For 3-Ø Supply
1. Underground (U.G) cable.
2. G.I Pipe
3. Pole
4. Pot Head
5. PVC double sheathed cables
6. Meter Board

5. 5
2.4 Standard wire size table, current ratings for Aluminium and copper conductors
Sl. No
Standard Copper Conductor Aluminium
Conductor
S.W.G No
Current in
Ampers
Area in
Sq.mm
Strands /
S.W.G No
1. 1 1/18 1.5 10
2. 1.5 3/22 2.5 16
3. 2.5 3/20 4 20
4. --- --- 6 27
5. 4 7/20 7 28
6. --- --- 10 34
7. 6 7/18 --- 36
8. --- --- 16 43
9. 10 7/16 --- 53
10. --- --- 25 59
11. --- --- 35 69
12. 16 19/16 --- 97
13. --- --- 70 134
14. --- --- 95 153
15. --- --- 120 198

6. 6
2.5 Standard wire (Aluminium or copper) size table and conduit pipe as per the size and
number of wires.
Size of cable Size of conduit (mm) Number of cables , maximum
Nominal
Cross
Section area
in Sq.mm
Number and
diameter
(in mm) of
wires
16 20 25 32 40 50
1 1/1.12 5 7 13 20 - -
1.5 1/1.40 4 6 10 14 - -
2.5 3/1.06 3 5 10 14 - -
4 7/0.85 2 3 6 10 14 -
6 7/1.40 - 2 5 9 11 -
10 7/1.40 - - 4 7 9 -
16 7/1.70 - - 2 4 5 12
25 7/2.24 - - - 2 2 6
35 7/2.50 - - - - 2 5
50 19/1.80 - - - - 2 3
2.6 Standard wire (Aluminium or copper) size table - For Underground (U.G) - Polycab 1.1KV
Aluminium Conductor PVC insulated Armoured and PVC Sheathed Cable IS : 1554
Nominal Cross Section area in Sq.mm Current Rating in Amps
2 Core or Twin Cable 3 core Cable
4 36 31
6 44 39
10 50 51
16 75 66
25 97 86
35 97 100
50 120 120
70 145 140
95 170 175
120 205 195
150 230 220
185 265 240
240 300 270
300 335 295
400 370 225
500 410 345
630 435 390
800 525 440
1000 570 490

7. 7
2.7 Single phase OH (Overhead) service connection – calculation, schedules (list) of
materials & Estimation of cost.
Example – 1, Prepare an estimate of cost for providing single phase overhead service main
connection to residential building having load of 4KW. The supplier pole is 15meter away
from the building.
Solution :
Calculation :
Total load = 4KW = 4000Watts
Total load current =
𝐿𝑂𝐴𝐷
𝑉𝑂𝐿𝑇𝐴𝐺𝐸
=
4000
230
= 17.39 Amps
Taking factor of safety 2 , (* sometime we can take it as Diversity factor 1.6)
Total load current = 17.39 × 2
= 34.78 Amps
Size of cable : From wiring table 16mm2 , Single Core Aluminium conductor, CTS (cab tyre
sheath) insulated cable
List of Materials :
1. 10 SWG G.I wire (messenger wire) = Span+ Extra= 15+2 = 17 Meter = 17/10 = 1.7Kg
2. 8 SWG G.I wire for Meter board Earthing = 01Kg
3. 16 mm
2
, 250V Single Core Aluminium Conductor Cable
= Span + Looping at pole & Consumer premise + Through GI pipe + For connection ) × 2
= (15+2+1.8+2 ) × 2 = 41.6 Meter ≈ ½ Coil
4. 1.1 KV Porcelain break insulator = 02 No’s
5. 1.1 KV Porcelain Reel insulator =Span×2 =15×2 = 30 No’s = 2 ½ Dozen
6. 38mm dia. 3mm thick G.I Pipe = Support Pipe + For Earthing = 1.8+2.5 = 4.3 meter
7. 25.4mm dia. 2mm thick PVC Pipe (Service Pipe) = 2meter
8. Clamp for fixing G.I Pipe =02 No’s
9. 25.4mm Diameter 2mm thick PVC Bends = 02 No’s
10. Binding wire = 1Kg
11. 450mm×450mm×65mm Teak wood meter board = 01 No’s
12. Miscellaneous Materials such as bolt nut, charcoal, salt etc,. = Lump sum

8. 8
Estimation of cost :
Sl.
No List of Materials with Specification
Quantity Required Rate /
Item
Amount
In `
Quantity Units
1. 10 SWG G.I wire (messenger wire) 1.7 Kg 50=00 85=00
2. 8 SWG G.I wire for Meter Board Earthing 01 Kg 50=00 50=00
3. 16 mm
2
, 250V Single Core Aluminium
Conductor Cable
½ Coil 1000=00 500=00
4. 1.1 KV Porcelain break insulator 02 No’s. 10=00 20=00
5. 1.1 KV Porcelain Reel insulator 2 ½ Dozen 25=00 62=50
6. 38mm dia. 3mm thick G.I Pipe 4.3 Meter 90=00 387=00
7. 25.4mm dia. 2mm thick PVC Pipe (Service
Pipe)
02 Meter 20=00 40=00
8. Clamp for fixing G.I Pipe 02 No’s. 30=00 60=00
9. 25.4mm Diameter 2mm thick PVC Bends 02 No’s. 20=00 40=00
10. Binding wire ½ Kg 50=00 25=00
11. 450mm×450mm×65mm Teak wood meter
board
01 No’s. 125=00 125=00
12. Miscellaneous Materials such as bolt nut,
charcoal, salt etc,.
Lump sum 1000=00
13. Stock Incidental @5% on Materials Cost ------------ 119=00
14. Labour Charge Lump sum 1500=00
15. Contingencies @5% on above -------------- 206=00
Grand Total `
4219=50
≈ 4220=00
2.8 Three phase OH (Overhead) service connection - calculation and schedules (list) of materials
& Estimation of cost.
Example :2, For Three Phase (3-Ø) Service Connection select the size and prepare an estimation
for overhead service connection to feed power supply to a factory of 10HP load for a distance of
10 meter.
Solution:
Calculation : Materials used for service connection, Assuming Supply voltage of 400V , p.f =0.8
and efficiency of load is 80%, 10HP load
Total load current =
Power
p.f × ɳ × V ×√3
=
10× 735.5
0.8×0.8×400×√3
= 16.6 Amps
Taking factor of safety 2 (*sometime we can take it as Diversity factor 1.6)
Total load current = 16.6 × 2
= 33.2 Amps
Size of cable : From wiring table 10mm2 Single Core Aluminium conductor, CTS (cab tyre sheath)
insulated cable.

9. 9
List of Materials :
1. 10 SWG G.I wire (messenger wire) = Span+ Extra= 10+2 = 12 Meter = 12/10 = 1.2Kg
2. 8 SWG G.I wire for Meter board Earthing = 01Kg
3. 10 mm
2
, 1.1 KV Voltage grade Single Core Aluminium Conductor Cable
= Span + Looping at pole & Consumer premise + Through GI pipe + For connection ) × 4
= (10+3+3+4) ×4 = 80 Meter ≈ 1 Coil (100meter)
4. 1.1 KV Porcelain break insulator = 02 No’s
5. 1.1 KV Porcelain Reel insulator =Span×4 = 10 × 4 = 40 No’s = 3 ½ Dozen
6. 50mm dia. 3mm thick G.I Pipe For supporting = 1.8 meter
7. 38mm dia. 3mm thick G.I Pipe For Earthing = 2.5 meter
8. 30mm dia. 2mm thick PVC Pipe (Service Pipe) = 2meter
9. Clamp for fixing G.I Pipe =02 No’s
10. 30mm Diameter 2mm thick PVC Bends = 02 No’s
11. Binding wire = ½ Kg
12. 500mm×400mm×65mm Teak wood meter board = 01 No’s
13. 30A Fuse Unit = 3 No’s
14. Miscellaneous Materials such as bolt nut, charcoal, salt etc,.= Lump sum
Estimation of cost :
Sl.
No List of Materials with Specification
Quantity Required
Rate / Item
Amount
In `
Quantity Units
1. 10 SWG G.I wire (messenger wire) 1.2 Kg 50=00 60=00
2. 8 SWG G.I wire for Meter Board Earthing 01 Kg 150=00 150=00
3. 10 mm
2
, 250V Single Core Aluminium
Conductor Cable
01 Coil 1000=00 1000=00
4. 1.1 KV Porcelain break insulator 02 No’s. 10=00 20=00
5. 1.1 KV Porcelain Reel insulator 3 ½ Dozen 25=00 87=50
6. 38mm dia. 3mm thick G.I Pipe 2.5 Meter 90=00 225=00
7. 30mm dia. 2mm thick PVC Pipe (Service
Pipe)
02 Meter 25=00 50=00
8. Clamp for fixing G.I Pipe 02 No’s. 30=00 60=00
9. 30mm dia. 2mm thick PVC Bends 02 No’s. 20=00 40=00
10. Binding wire ½ Kg 50=00 25=00
11. 500mm×400mm×65mm Teak wood meter
board
01 No’s. 600=00 600=00
12. 30A Fuse Unit 03 No’s 100=00 300=00
13. Miscellaneous Materials such as bolt nut,
charcoal, salt etc,.
Lump sum 1000=00
14. Stock Incidental @5% on Materials Cost ------------ 181=00
15. Labour Charge Lump sum 1500=00
16. Contingencies @5% on above -------------- 265=00
Grand Total ` 5563=50
≈
5570=00

10. 10
2.9 Single phase UG service Connection - Calculation and schedules (list) of materials &
Estimation of cost.
Example : 3, Prepare an estimate of cost for underground service connection to feed power
supply to an AEH installation having a lighting load of 1200watts and heating load of 3KW for
distance of 15 meters.
Solution :
Calculation :
Load Current =
𝐓𝐨𝐭𝐚𝐥 𝐥𝐨𝐚𝐝
𝐒𝐮𝐩𝐩𝐥𝐲 𝐕𝐨𝐥𝐭𝐚𝐠𝐞
=
𝟏𝟐𝟎𝟎+𝟑𝟎𝟎𝟎
𝟐𝟑𝟎
= 18.26 Amps
Allowing factor of safety 3 Times, Load current = 18.26 × 3 = 54.78 Amps
From the wiring table 10 sq.mm , twin core , steel Armoured Aluminium UG cable 1.1KV class.
List of Materials :
1. Length of 10 sq.mm UG cable =
(Horizontal distance + 4.5m pole side + 3.5 Building Side + looseness )
= 15 + 4.5 + 3.5 +2 = 25 meter.
2. Iron pot head suitable for 10 sq.mm twin core 1.1KV Class – 1 No.
3. G.I pipe for cable drawing 40mm dia, 3mm thick = 3meter pole side + 3 meter building side
= 3+3 = 6 meter.
4. No. of G.I bends 40 mm dia, 3mm thick - 3 No’s
5. Clamps for G.I Pipe & Pot head fixing - 4 Sets
6. Size of PVC double sheathed cable for pole side connection,
Load current = 18.26 Amps
Factor of Safety 2 ,
Total Load Current = 18.26 × 2 = 36.52 Amps
From the wiring table 16sq.mm , Aluminium PVC double Sheathed 250V graded wire.
Length of 16 sq.mm double Sheathed PVC wire = 6 × 2 = 12meter.
7. G.I Earth electrode (pipe) 40mm dia, 3 mm thick = 2.5 meter.
8. G.I Earthing conductor 8 SWG - 1Kg.
9. Meter board 300×300×65 mm Varnished Teak wood - 1 No.
10. Fuse Unit with Cut-out = 18.26×(3 Factor of Safety) = 54.78 ≈ 60 Amps - 1No
11. Bricks 23×11.5×7.5 cm = 15 × 100/23 = 65.21 ≈ 66 Nos.
12. Bituminous Compound = 1 Kg.
13. Miscellaneous materials Charcoal , salt , bolts, Nuts , Clamp, cement, sand , Screw etc. =
Lumpsum.

11. 11
Estimation of cost :
Sl.
No List of Materials with Specification
Quantity Required
Rate / Item
Amount
In `
Quantity Units
1. UG Cable Aluminium 10 Sq.mm Twin Core
Steel Armoured 1.1KV grade
25 Meter 75=00 1875=00
2. Iron pot head suitable for 10 sq.mm twin core
1.1KV Class
01 No. 225=00 225=00
3. G.I pipe for cable drawing 40mm dia, 3mm
thick
06 Meter 180=00 1080=00
4. G.I bends 40 mm dia, 3mm thick 03 No’s 95=00 285=00
5. Clamps for G.I Pipe & Pot head fixing 04 Sets 60=00 240=00
6. 16 sq.mm double Sheathed PVC wire 12/100 Coil 1200=00 144=00
7. G.I Earth electrode (pipe) 40mm dia, 3 mm
thick
2.5 Meter 180=00 450=00
8. G.I Earthing conductor 8 SWG 01 Kg 60=00 60=00
9. Meter board 300×300×65 mm Teak wood 01 No. 300=00 300=00
10. Fuse Unit with Cut-out 60Amps 01 No. 200=00 200=00
11. Bricks 23×11.5×7.5mm 66 No’s 04=00 264=00
12. Bituminous Compound 01 Kg 100=00 100=00
13. Miscellaneous materials Lumpsum 200=00
14. Labour Charges (Laying cable & Earthing ) ------------ 1500=00
15. Contingencies @5% on above ------------ 346 =00
Grand Total `
7269=00
≈7270=00

12. 12
2.10 Three phase UG service Connection - Calculation and schedules (list) of materials &
Estimation of cost.
Example : 4, Prepare the estimate of cost for underground service main to feed power supply to
workshop of load 15HP for a distance of 10Meter.
Solution :
Calculation : Materials used for service connection, Assuming Supply voltage of 415V , p.f =0.8
and efficiency of load is 80%, 15HP load.
Load Current =
Power
p.f × ɳ × V ×√3
=
15× 735.5
0.8×0.8×415×√3
= 23.97 Amps
Allowing factor of safety 2 Times, Load current = 23.97 × 2 = 47.95 ≈ 48Amps
From the wiring table 16 sq.mm , Three & half core with steel Armoured Aluminium UG cable
1.1KV class is selected.
List of Materials :
1. Length of 16 sq.mm UG cable =
(Horizontal distance + 4.5m pole side + 3.5 Building Side + looseness )
= 10 + 4.5 + 3.5 +2 = 20 meter.
2. Iron pot head suitable for 16 sq.mm, Three core 1.1KV Class – 1 No.
3. G.I pipe for cable drawing 50mm dia, 3mm thick = 3meter pole side + 3 meter building side
= 3+3 = 6 meter.
4. No. of G.I bends 50 mm dia, 3mm thick - 3 No’s
5. Clamps for G.I Pipe & Pot head fixing - 4 Sets
6. Size of PVC double sheathed cable for pole side connection,
From the wiring table 16 sq.mm , Aluminium PVC double Sheathed 1.1KV Voltage grade.
Length of 16 sq.mm double Sheathed PVC wire = 6 × 4 = 24 meter.
7. G.I Earth electrode (pipe) 40mm dia, 3 mm thick = 2.5 meter.
8. G.I Earthing conductor 8 SWG - 1Kg.
9. Meter board 500×750×45mm Varnished Teak wood - 1 No.
10. Fuse Unit with Cut-out = 23.97 ×(3 Factor of Safety) = 71.91≈ 70 Amps - 1No
11. Bricks 23×11.5×7.5 cm = 10 × 100/23 = 43.47 ≈ 45 Nos.
12. Bituminous Compound = 1 Kg.
13. Miscellaneous materials Charcoal , salt , bolts, Nuts , Clamp, Cement, sand Screw etc. =
Lumpsum.

13. 13
Estimation of cost :
Sl.
No List of Materials with Specification
Quantity Required
Rate / Item
Amount
In `
Quantity Units
1. UG Cable Aluminium - 16 Sq.mm 3 ½ Core Steel
Armoured, PVC insulated ,1.1KV grade
20 Meter 350=00 7000=00
2. Iron pot head suitable for 16bsq.mm 3-core
1.1KV Class
01 No. 700=00 700=00
3. G.I pipe for cable drawing 50mm dia, 3mm
thick
06 Meter 300=00 1800=00
4. G.I bends 50 mm dia, 3mm thick 03 No’s 100=00 300=00
5. Clamps for G.I Pipe & Pot head fixing 04 sets 60=00 240=00
5. 16 sq.mm double Sheathed PVC wire 24/100 Coil 2000=00 480=00
6. G.I Earth electrode (pipe) 40mm dia, 3 mm
thick
2.5 Meter 250=00 625=00
7. G.I Earthing conductor 8 SWG 01 Kg 150=00 150=00
8. Meter board 500×750×45mm Teak wood 01 No. 900=00 900=00
9. Fuse Unit with Cut-out 70Amps, 500V graded 01 No. 300=00 300=00
10. Bricks 23×11.5×7.5mm 45 No’s 20=00 900=00
11. Bituminous Compound 01 Kg 100=00 100=00
12. Miscellaneous materials Lumpsum 600=00
13 Labour Charges (Laying cable & Earthing ) ------------ 1500=00
14. Contingencies @5% on above ------------ 780=00
Grand Total `
16375=00
≈16380=00