Short note: Earthing system

Earthing (grounding) is the connection of the non-current-carrying metal parts of an electrical installation (or the neutral of the supply) to the general mass of the earth through a low-resistance conductor.

Purposes:

• To protect people from electric shock if the insulation fails and the metal body becomes live.
• To give a path for fault current, so that fuses/MCBs/ELCBs operate quickly.
• To keep the voltage of the system stable with respect to earth, and to protect equipment from lightning and surges.

 Appliance body --- earth wire (green/yellow) ---+
                                                  |
                                 Earth electrode (pipe/plate)
                                 buried in soil with salt + charcoal

Methods of earthing:

1. Plate earthing: a copper plate (60 cm x 60 cm x 3 mm) or GI plate (60 cm x 60 cm x 6 mm) buried vertically about 3 m deep in alternate layers of charcoal and salt.
2. Pipe earthing: a perforated GI pipe (about 38-50 mm diameter, 2-3 m long) driven vertically into the ground; water is poured in to keep the soil moist. It is the most common type.
3. Rod earthing: a copper or GI rod driven into the ground.
4. Strip/wire earthing: a GI strip laid in a trench.

The earth resistance should be as low as possible, typically below 5 Ω for a house (about 0.5-1 Ω for power stations and large substations). It is checked with an earth tester, and the electrode is watered in dry seasons.