Question

What is the function of an earth wire?why is it necessary to earth metallic appliances?

Answer 1

The main function of the earth wire is to conduct the leaking current  from the electrical appliance to the ground . It is conected to the outer metallic body of the appliance .

It is necessary to earth metallic appliances , as it protects the user from electric shocks by transferring the current to the earth.

Answer 2

     Earth wire or Earthing connection in the electrical wiring at home is connected to a large capacity storage of metallic or salted materials.  These materials drain electric charge if it is present on the wire and make the charge/voltage potential on the wire to 0.

     Usually the metallic bodies of the electric appliances are connected to the Earthing in the 3-way plug connections.  If there is a surge in the electric power supply or if there is a short circuit some where, then the high voltage and the excess current flow in to the Earthing connection.  So the appliance is secure from damage. 

    If the electric wiring in the house or in the appliance is faulty and as a result, the metallic body of the appliance carries electricity/charge on it.  Then the high voltage or leaked charges flow in to the earth.  This saves us from electric shocks when we touch the appliances.