The scope of this specification covers the supply, installation and testing and earthing system of the entire installation and for lightning protection.
The following standards shall be applicable, however, contractor shall comply with the latest or superseded versions of IS/BIS to be used for the complete work:
- IS 3043 1966: Code of practice of earthing.
- IS 2309 1969: Code of practice for the protection of building and allied structures against lightning.
- The earthing system shall comprise of earth electrodes at substation and other convenient places, with an interconnecting earth grid.
- The earth electrodes shall be in conformity with IS 3043 of plates or pipes of GI with test links, internal connecting leads, earthing mixture of salt, charcoal, etc. The number of each electrodes shall be determined from measurement of the earth resistance which finally should not exceed 1 ohms.
- The earth conductors shall be of GI of minimum cross section as 200 sq. mm. As far as possible, all earth electrodes shall be interconnected to form an earthing grid, by means of earth conductors. All joints in the grid shall be welded or riveted. Connections of the grid for the equipments shall be of GI or copper wires and all such terminations of wires be with soldered cable lugs.
- All cables and conduits shall have continuously run earth wires of specified gauges, securely fastened to the main earthing grid. The hardware used shall be galvanized steel or brass.
- Earth conductors on wall, structures shall be installed with proper clamps and saddles. Earth conductors when crossing through walls shall be passed through GI pipes.
- The layout of the earth electrodes and earthing conductors shall be first approved by the Authorities before commencing the work.
- Large Motors, Switchboards - HT & LT, Transformers, DG Sets, etc. shall have earthing GI strips of appropriate cross-section to carry the full short circuit current. Similar motors, DBs wiring conduits shall have earthing GI wires of appropriate cross section.
- The lightning protection system shall comprise of lightning earthing terminals, roof conductors, down conductors, test links and earth electrodes.
- Each down conductor shall have a separate earth electrode of GI pipe as per IS 2309.
- The number of down conductors and earth terminals shall be determined from the Risk index as per IS 2309.
- All terminals and roof conductors shall be interconnected by welding or revetting to form a continuous grid. Water, steam and other service pipes shall not be used for interconnections.