AQA GCSE Earth Wire

Earth Wire

The Earth wire of a circuit, connects the metal case of the appliance to Earth as shown below.

The Earth wire should have a potential difference of 0V.

A current only flows along the appliance if the appliance becomes faulty.

In the case below the live wire has broken from its contact and is now touching the metal case, so electrical charge is flowing onto the case.

The Earth wire will allow the electrical charges that are flowing onto the case to flow directly to Earth. This prevents the charges building up and prevents someone receiving an electric shock if they touch the metal case.

If a person touches the metal case, and the appliance is not Earthed as shown below:

Then the electrical charge that flowed onto the case from the Live wire has built up. When the person touches the case, the charge flow onto the person and they receive an electric shock!

Double insulated or plastic cased appliances do not need an Earth wire, because their cases are insulators.