Earthing is the process of making metallic connection of the body to the earth (which is at zero potential) for the safety of the human body from shocks.

Generally all metallic covers of machines, starter or sheathing of wiring are electrically dead.

Due to failure of insulation or bad workmanship, they can become alive.

If we touch such faulty parts of machine or installation, we will receive a serious shock.

To avoid this, all metallic covers and frames of machines has to be earthed.

An earthing system should have very low resistance and easily allow the leakage current through it.

Objectives of Earthing:

Earthing is should be done to achieve the following objectives:

1. To save human life from danger or shock or death by blowing fuse of any apparatus which becomes leaky.

2. To protect large building from atmospheric lightning.

3. To protect all machines fed from overhead lines from lightning investors

4. To maintain the line voltage constant ( since neutral of every alternator, transformer is earthed).

The general rules for earthing are given below:

1. The earthing must be continuous by a single solid conductor in a house wiring system.

   All metallic covering of the main switch, distribution box, electrical equipment, ceiling fans etc. along with the earth of the walls socket should be earthed.

2. All medium voltage machine metallic covers should be earthed by two separate earth connections.

3. The earth resistance of the electrode should not exceed 3 ohm for ordinary soil. The earth resistance of the electrode should not exceed 8 ohm for rocky soil.