EARTHING SYSTEMS:

1

Earthing of H.T. & LT Line supports

i) ON Metal supports

:

Every fifth pole all supports provided with mass or block concrete foundation should be earthed

ii) On RCC Poles

:

The metal cross arm and the insulator pints shall be bonded together and earthed at every pole H.T. Lines and every fifth pole for L.T. Lines

2

All special structures carrying switches, Transformers, fuses etc. should be earthed

3

The supports on either side of Road, Railways or River crossing should be earthed

4

All supports Metal , Wood or RCC or both H.T. & LT lines running through inhabited locations, road crossing and l along such other places where earthing of all poles is considered describe from safety consideration should be earthed.

5

In special locations Railways & Telepraph crossings , special structures etc. pipe earth by means of 25 mm GI pipe driven 2.5 to 3mts into the ground should be adopted.

At other locations coil earth consisting of 10 mtrs. Length of no 8 SWG GI pipe wire compressed into coil 1 mtr. Length and diameter 75 to 100 mm and buried 1.5 mtr. Deep should be adopted.

6

The ohmic resistance of earth should not exceed 10 phms.

7

Plate Earth :

a) Large Power Station and Major Sub Stations:

:

120x 120 cms. Iron plates of 12.5 thick.

b) Small Stations:

:

60 x60 cms cast Iron plates of 9.4 mm thick

8

Pipe Earthings :

a) Large Power Station and Major or Sub Stations long

:

Cast iron pipes 152 mm dia 3 Nos of 0.48 mts not less than 12.7 mm thick

b) Small Stations

:

G.I Pipe 50.0 mm dia and 3 mts. Long

9

Earth Connections :

a) Main and subidiary earth connections

:

Not less than 161 sq.mm

b) Branch Connections

:

Not les than 64.5 sq.mm

10

Earth Resistance :

Station

Combined Resistance of Earth in the station on Ohms, (Max)

a) Large Power Station

0.5

b) Major Sub Station

1.0

c) Small Station

2.0