EARTHING SYSTEMS: |
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1 |
Earthing of H.T. & LT Line supports |
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i) ON Metal supports |
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Every fifth pole all supports provided with mass or block concrete foundation should be earthed |
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ii) On RCC Poles |
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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 |
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2 |
All special structures carrying switches, Transformers, fuses etc. should be earthed |
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3 |
The supports on either side of Road, Railways or River crossing should be earthed |
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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. |
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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. |
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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. |
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6 |
The ohmic resistance of earth should not exceed 10 phms. |
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7 |
Plate Earth : |
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a) Large Power Station and Major Sub Stations: |
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120x 120 cms. Iron plates of 12.5 thick. |
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b) Small Stations: |
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60 x60 cms cast Iron plates of 9.4 mm thick |
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8 |
Pipe Earthings : |
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a) Large Power Station and Major or Sub Stations long |
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Cast iron pipes 152 mm dia 3 Nos of 0.48 mts not less than 12.7 mm thick |
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b) Small Stations |
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G.I Pipe 50.0 mm dia and 3 mts. Long |
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9 |
Earth Connections : |
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a) Main and subidiary earth connections |
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Not less than 161 sq.mm |
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b) Branch Connections |
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Not les than 64.5 sq.mm |
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10 |
Earth Resistance : |
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Station |
Combined Resistance of Earth in the station on Ohms, (Max) |
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a) Large Power Station |
0.5 |
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b) Major Sub Station |
1.0 |
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c) Small Station |
2.0 |
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