Question

Why is the metal covering of an electrical appliances earthed

Answer 1

To reduce the risk of getting shocked the manufacturer keep in their mind to keep us safe....

Answer 2

We would get an electric shock if the live wire inside an appliance, such as a cooker, came loose and touched the metal casing. However, the earth terminal is connected to the metal casing so that the current goes through the earth wire instead of causing an electric shock.