Earthing is used to protect you from an electric shock.
Answered by Dave, Electrical Safety Expert
If there is a fault in your electrical installation you could get an electric shock if you touch a live metal part. This is because the electricity may use your body as a path from the live part to the earth part.
Earthing is used to protect you from an electric shock. It does this by providing a path (via a protective conductor) for fault current to flow to earth. It also causes the protective device (either a circuit-breaker or fuse) to switch off the electric current to the circuit that has the fault.
For example, if a cooker has a fault, the fault current flows to earth through the protective (earthing) conductors. A protective device (fuse or circuit-breaker) in the fusebox (consumer unit) switches off the electrical supply to the cooker. The cooker is now safe from causing an electric shock to anyone who touches it.