Estimation Costing of Overhead Service For A Single and Three Phase

July 24, 2020February 21, 2022 CS Electrical And Electronics

Hello everyone, in this article I will discuss the estimation costing of overhead service for a single phase and three phase with example. You can also catch me @ Instagram – Chetan Shidling.

Before starting the article if you want to watch a video related to electrical estimation and costing, you can watch my YouTube videos – Click Here.

Also read – Battery Management System Questions And Answers.

Estimation Costing of Overhead Service

First, I will discuss what is overhead service mains.

The name overhead says that the conductors are drawn from above the ground level. The overhead line consists of service cables, reel insulators, broken insulators, messenger wire, GI pipe, service pipe, etc.

The advantages of overhead service mains are easy to erect, easy to find fault, the cost is less, etc and the disadvantages of overhead service mains are it is not safe, affected by sun or rain, ugly appearance, etc.

Single Phase Overhead Service Mains Calculation

Q: Prepare a list of material and estimate the cost for providing service connection to a building at 240 V single phase 50 Hz having a light and fan load of 2 KW and heating load of 2 KW. The supply is to be given from an overhead line 20 m. away from the building.

Solution: Materials used for service connection :

To calculate the size of the wire first you need to calculate the total connected load in the house and then calculate the load current of the house using proper formula.

Connected load = lighting load + heating load

= 2 KW + 2 KW = 4000 W

See a total load of house is 4000 W, multiply it by a factor of safety, the factor of safety means we should consider future load, now itself I will consider future load double of the present, so I will multiply by 2.

Keeping in view the future additional demand ( say 100% ) lets the future load be twice the present load (i.e. a factor of safety of 2). i.e. 2 × 4000 W = 8000 W.

Load current in amperes = Load in watts/Rated voltage

= 8000/240

= 33 Amps.

The load current of the house is 33 Amps, now by see the wire table you can find the size of the wire. Watch my video how to find the size of the wire – Click Here

The size of the aluminum cable is 10 sq mm from the wire table.

(a) The length of cable required

= (20 + 6 + 3 + 4) × 2

= 66 m

We should calculate the length of cable from low tensions lines to the consumer meter board, below I will provide formulas on how to calculate the length of cable.

Note: Lenght of the cable = Horizontal length (20 m) + Looseness and meter board connection (6 m) + Service pipe lenght (3 m) + Pole side connection (4 m)

Horizontal length – Length of cable from a pothead up to service pipe.

Looseness and meter board connection – length of cable from the end of the service pipe to the meter board.

Service Pipe – The cables are drawn inside the service pipe, so we should consider that length also.

Pole side connection – The cables used to connect low tension lines to pothead that length also we should consider.

(b) No of Break Insulators = 2 Nos

The number of break insulators required is 2 No. Only two break insulators are used in overhead service mains. one insulator at the pole side and another insulator at the meter board side. Break insulators are used to isolate messenger wire from the pole and also to give support for messenger wires.

(c) No of Reel Insulators = 2(20 + 6) = 52 Nos

The number of reel insulators required is 52 No. The purpose of reel insulators is to provide some distance between two conductors and it will also avoid short circuits between two conductors if both the conductor’s insulation has been damaged.

(d) 10 SWG G.I wire for messenging = 22m = 2 kg.

The purpose of messenger wire is to give support to the reel insulators and also to the service cables.

(e) 30 mm PVC pipe of 2 m and bends of 3 Nos.

(f) 40 mm G.I pipe of 3 mm thick 1.8 m for supporting.

(g) 500 mm × 500 mm × 45 mm WVTWB – 1 No.

(h) 40 mm G.I pipe 2.5m and l kg 8 SWG G.I. wire for earthing.

(i) 30 A fuse of 2 Nos and Miscellaneous materials.

Miscellaneous materials mean nut, bolt, etc.

These are the Materials required.

Costing Of Single Phase Overhead Service Mains

SI.No	Particulars	Unit	Quantity	Rate In Rupees	Cost In Rupees
01	10 sq mm aluminium 11000 v grade double sheathed PVC cable	100 M (coil)	66M	1800	1188.00
02	1.1 KV porcelain break insulator	No’s	2	10.00	20.00
03	Reel insulators	No’s	52	2.00	104.00
04	10 SWG GI wire for messenging	Kg	2	100.00	200.00
05	40 mm 3 mm thick GI pipe for supporting	M	1.8	375.00	675.00
06	30 mm PVC pipe 2 mm thick for servicing	3 M	2 M	65.00	43.33
07	PVC bends	No’s	3	10.00	30.00
08	500 * 500 * 45 mm well seasoned varnished teak wood (WVTB)	No	1	600.00	600.00
09	40 mm GI pipe 3 mm thick for earthing	M	2.5	375.00	937.50
10	8 SWG GI wire for earthing	Kg	1	150.00	150.00
11	30 A 500 voltage grade porcelain fuse	No’s	2	100.00	200.00
12	12.5 mm dia 300 eye bolt nuts of M.S	No’s	2	50.00	100.00
13	Miscellaneous materials such as binding wire clamps for pole and service pipe bolts, nuts, coal, salt, etc.	Lump sum			525.67
14	Labour charges
	(a) for serving and earth work				700.00
15	Contingencies and unforesen things @ 5% on above amount.				260.10
				Total=	5460.00

Three Phase Overhead Service Mains Calculation

Q: Three phases overhead service connection: select the size and prepare an estimate for overhead service connection to feed power supply to a factory of 10 HP load for a distance of 10 meters.

Solution: Materials used for service connection.

Assuming a supply voltage of 400 V, p.f = 0.8 and the efficiency of the load is 80%.

Current = (10×735.5)÷(0.8×0.8×400×√3) = 16.6 Amps

Keeping view the future additional demand says 100% let the future load be twice of present load or factor of safety as 2, the current rating is 33A.

The size of the aluminum cable required is 10 sq mm.

(a) Lenght of the cable = 10+3+3+4 = 20 × 4 = 80 m.

Note: Lenght of the cable = Horizontal length (10 m) + Looseness and meter board connection (3 m) + Service pipe lenght (3 m) + Pole side connection (4 m).

(b) G.I Messenging wire = 10 + 1 = 11m = 1kg.

(c) No of Break Insulators = 2 Nos.

(d) No of Reel Insulators = (10+3)4 = 13 × 4 = 52 Nos.

(e) 30 mm PVC pipe of 2 m and of 3 bends.

(f) 50 mm G.I pipe of 3 mm thick 1.8 m for supporting.

(g) 500 × 500 × 65 m WVTWB – 1 No.

(h) 40 mm G.I pipe 2.5 m and 1 kg 8 SWG GI wire for earthing.

(i) 30 A fuse unit – 3 Nos.

(j) M.S. clamps with nuts and bolts – 2 sets and miscellaneous materials.

Costing Of Three Phase Overhead Service Mains

SI.No	Particulars	Unit	Quantity	Rate in rupees	Amount in rupees
01	10 sq mm aluminium cable of 1.1 KV voltage grade, double sheathed	100M (coil)	80 M	1800.00	1440.00
02	1.1 KV porcelain break insulators	No’s	2	10.00	20.00
03	Porcelain reel insulators	No’s	52	2.00	104.00
04	10 SWG GI messanging wire	Kg	2	100.00	200.00
05	30 mm PVC pipe of 2 mm thick, for servicing	3 M	2	65.00	130.00
06	PVC bends for 30 mm PVC pipe	No’s	3	10.00	30.00
07	50 mm GI pipe 3 mm thick 1.8M for supporting	M	1.8	495.00	891.00
08	500 * 500 * 45 mm WVTWB	No	1	600.00	600.00
09	30 A porcelain fuse unit 500 Vg	No	3	100.00	300.00
10	40 mm GI pipe 3 mm thick	M	2.5	375.00	937.00
11	8 SWG GI wire for earthing	Kg	1	150.00	150.00
12	12.5 mm dia 300 mm eye bolt nuts of M.S	No	2	50.00	100.00
13	Miscellaneous materials such as binding wire, nuts, bolts, cement, salt, coal, etc.	Lump sum			298.00
14	Labour charge
	(a) For earthing				300.00
	(b) For servicing				700.00
15	Contingencies and unforseen things @ 5% on above amount				260.00
				Total=	Add all

I hope this article may help you all a lot. Thank you for reading. If you have any doubts related to this article “estimation costing of overhead service”, then comment below.

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