Electricity

Mains Electricity - Earthing.

If the outer casing (the outside bit) of an appliance
is a conductor (made of metal), then it can be made safe by Earthing.

The Earth wire usually carries no electricity,
it is connected to the metal case on the inside of the appliance.

Earth Wire Connection
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<img src="Earth-Wire-Connection.gif" height="100" width="100"><br>
If something goes wrong inside the appliance
and the Live wire touches the metal case,
then the Earth wire acts like a Neutral wire
and completes the circuit for the electricity.
A very large current suddenly flows
because the metal case has little resistance.
This large current blows the fuse in the plug
and disconnects the appliance from the power supply.