Question

what is the function of an earth wire in a domestic electric circuit?

Answer 1

We can receive an electric shock on touching a running appliance. This is caused by the leakage of current from the appliance. Earthing provides a safety measure against the electric shock, caused by the leakage of current. Thats why a third wire (Earth wire) is used in domestic wiring.

Sometimes, the insulation of a live wire burns due to excessive heating. A naked live wire may lead to an electrical shock. To protect the appliance against an electrical shock, its metallic case is connected with the Earth wire.