Overhead service mains

Estimation Costing of Overhead Service For A Single and Three Phase

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.NoParticularsUnitQuantityRate In RupeesCost In Rupees
0110 sq mm aluminium 11000 v grade double sheathed PVC cable100 M
(coil)
66M18001188.00
021.1 KV porcelain break insulatorNo’s210.0020.00
03Reel insulatorsNo’s522.00104.00
0410 SWG GI wire for messengingKg2100.00200.00
0540 mm 3 mm thick GI pipe for supportingM1.8375.00675.00
0630 mm PVC pipe 2 mm thick for servicing3 M2 M65.0043.33
07PVC bendsNo’s310.0030.00
08500 * 500 * 45 mm well seasoned varnished teak wood (WVTB)No1600.00600.00
0940 mm GI pipe 3 mm thick for earthingM2.5375.00937.50
108 SWG GI wire for earthingKg1150.00150.00
1130 A 500 voltage grade porcelain fuseNo’s2100.00200.00
1212.5 mm dia 300 eye bolt nuts of M.SNo’s250.00100.00
13Miscellaneous materials such as binding wire clamps for pole and service pipe bolts, nuts, coal, salt, etc.Lump
sum
525.67
14Labour charges
(a) for serving and earth work700.00
15Contingencies 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.NoParticularsUnitQuantityRate in rupeesAmount in rupees
0110 sq mm aluminium cable of 1.1 KV voltage grade, double sheathed100M
(coil)
80 M1800.001440.00
021.1 KV porcelain break insulatorsNo’s210.0020.00
03Porcelain reel insulatorsNo’s522.00104.00
0410 SWG GI messanging wireKg2100.00200.00
0530 mm PVC pipe of 2 mm thick, for servicing 3 M265.00130.00
06PVC bends for 30 mm PVC pipeNo’s310.0030.00
0750 mm GI pipe 3 mm thick 1.8M for supportingM1.8495.00891.00
08500 * 500 * 45 mm WVTWBNo1600.00600.00
0930 A porcelain fuse unit 500 VgNo3100.00300.00
1040 mm GI pipe 3 mm thickM2.5375.00937.00
118 SWG GI wire for earthingKg1150.00150.00
1212.5 mm dia 300 mm eye bolt nuts of M.SNo250.00100.00
13Miscellaneous materials such as binding wire, nuts, bolts, cement, salt, coal, etc.Lump sum298.00
14Labour charge
(a) For earthing300.00
(b) For servicing700.00
15Contingencies and unforseen things @ 5% on above amount260.00
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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