Under CEAR, rule 41, there is specific provision of earthing neutral wire of a 3-phase, 4-wire system and the additional third wire of a 2- phase, 3-wire system. Earthing is to be done with two separate connections. Grounding system also to have minimum two or more earth pits (electrode) such that proper grounding takes place. As per the rule 42, installation with load above 5 kW exceeding 250 V shall have suitable Earth leakage protective device to isolate the load in case of earth fault or leakage. Neutral and earth run separately on overhead line/cables. Separate conductor for overhead lines and armouring of cables are used for earth connection. Additional earth electrodes/pits are installed at user ends for proper earth. All metal casing or metallic coverings of electric supply line or apparatus to be connected with earth and all such earthling points shall be so joined to make good mechanical and electrical connection in complete system.
Earthing in mines Earthing in an underground mine shall be carried out by connection to an
earthing system at the surface of the mine as per rule 99. As per rule 100, protective equipment is to be placed in the mines for automatic disconnection of supply when there is earth fault exceeding 750 milliampere in 250 V to 1000 Volt installations. For open cast mine the limit is 50 ampere in installations of voltage exceeding 1100 V and up to 11 kV. The earth leakage current is to be restricted by placing suitable neutral grounding resistance (NGR) in all the distribution transformers. ==Salient features==