Tower Earthing

Tower footing resistance (TFR) of each tower after it has been erected and before the stringing of the earthwire shall be measured during dry weather. Each tower shall be earthed and the tower footing resistance shall not exceed 10 ohms. Pipe type earthing and counter poise type earthing wherever required shall be done in accordance with the latest additions and revision of

IS : 3043	Code of practice of Earthing
IS:5613	Code of practice for Design, Installation and maintenance (Part-III/ section 2) of overhead power lines

The provision of holes on stubs shall be made as per approved earthing drawings. The earthing will vary depending on soil resistivity.

Pipe Earthing: At locations where pits can be excavated, the towers shall be earthed by pipe earthing. The grounding shall be effected by making about 325 mm dia and 3850 mm deep pit at a distance of not less than 3650 mm diagonally away from the stubs and filling in the pits with finely broken coke having granule sizes not more than 25 mm thick. The coke shall be maintained up to a distance of 150 mm from the pipe on all sides. The top edge of the pipe shall be at least 600 mm below the ground level. The steel strip shall be buried not less than 600 mm deep from the ground level. The earth flat shall be of G.I. Pipe shall be of 25mm dia and 3050mm long class-B, with 6mm holes at 150mm apart and GI flat shall be 50x6mm, 4050mm long.

Counterpoise Earthing: In locations of high resistivity soils especially in rocky locations special earthing arrangement shall be employed in the form of counterpoise earth to bring down the tower footing resistance to 10 ohms. The counterpoise earth shall consist of 4 Nos. 7/3.15mm galvanized steel wires running radially from all the four tower legs for a distance of about 15 to 70 meters. The galvanized steel wire shall be connected to the tower legs by galvanized steel lugs forged or compressed at its one end, complete, with 16 mm (5/8") dia bolts and nuts, required for connecting the earthing to the tower and the other ends of the earthwire shall be connected to an electrode of 20mm dia and 600mm long, and the counterpoise shall be buried radially from the tower base at 600 mm below/ground level. The lugs should be preferably covered in chimney portion of the foundation to avoid pilferage. For soil resistivity less than 1500 Ohm-meter, earthing shall be established by providing 4 length of 30 meter counterpoise wire (Total 120m length wire). Otherwise for soil resistivity greater than 1500 Ohmmeter, earthing shall be established by providing 4 length of 70m counterpoise wire (Total 280 m length wire)