8.1 General

Earthing shall generally be carried out in accordance with the requirements of Indian Electricity Rules, 1956 as amended time to time and the relevant regulations of the Electricity Supply Authority concerned.

The main earthing system of an electrical installation must consist of:

    a) An earth electrode;

    b) A main earthing wire;

    c) An earth bar (located on the main switchboard) for the connection of the main earthing wire, protective earthing wires and/or bonding wires within the                      installation; and

    d) A removable link, which effectively disconnects the neutral bar from the earth bar.

    (NOTE — The requirements of (c) and (d) above must be carried out by the licensed electrician as part of the switchboard installation.)

The main earthing wire termination must be readily accessible at the earth electrode.

The main earthing wire connection must:

    a) be mechanically and electrically sound;

    b) be protected against damage, corrosion, and vibration;

    c) not place any strain on the various parts of the connection;

    d) not damage the wire or fittings; and

    e) be secured at the earth electrode

Use a permanent fitting (like a screwed-down plastic label or copper label, or one that can be threaded onto the cable) at the connection point that is clearly marked with the words: “EARTHING LEAD — DO NOT DISCONNECT” or “EARTHING CONDUCTOR — DO NOT DISCONNECT”.

8.1.1 All medium voltage equipment shall be earthed by two separate and distinct connections with earth. The contact area of earth conductor/plate shall be determined using guidelines specified in IS 3043.

Medium voltage systems of 400/230 V, 4-wire, 3-phase, systems are normally operated with the neutral solidly earthed at source. At medium voltage, Indian Electricity Regulations require that the neutral be earthed by two separate and distinct connections with earth. Source in the case of a substation (such as 11kV/ 400 V) would be the neutral(s) of the transformer(s). Neutral conductor of half the size of the phase conductor was permitted in earlier installations. But with the proliferation of equipment using non-linear devices and consequent increase in harmonics, the neutral will carry a current more than the notional out- of-balance current and as such neutral conductor shall be of the same size as the phase conductor.

In the case of high and extra high voltages, the neutral points shall be earthed by not less than two separate and distinct connections with earth, each having its own electrode at the generating station or substation and may be earthed at any other point provided no interference is caused by such earthing. The neutral may be earthed through suitable impedance. Neutral earthing conductor shall be sized at to have a current carrying capacity not less than the phase current.