why a ground wire is used in a circuit?what is its function?

A ground wire links the external body of an electrical
appliance to the Earth which is a large conductor.

The
function of a ground wire can be explained in a better way by taking an
example.

Let us consider a washing machine. There is a
large motor in the washing machine with a high power rating. Under ideal conditions,
adequate insulation in the machine prevents any voltage from being created on the outer
metallic box in which the motor is enclosed. If the insulation is damaged or water
enters the engine a path of conduction is created that leads to a voltage being created
on the outer body of the washing machine.

If you were
operating the machine and touched it, you will experience a shock as current passes
through your body into the Earth.This can be very
dangerous.

Therefore it is essential to have a ground or
Earth wire that connects the outer body of the machine to the Earth and ensure that even
if anything were to go wrong and a voltage created on the outer surface it is quickly
dissipated and the user does not suffer any harm.