— based on https://www.bbc.co.uk/bitesize/guides/z886b82/revision/2
plugs:
| Live wire | Copper wire coated brown along which the current enters the device. This is the wire that is at 230 V and is connected to the fuse. |
| Neutral wire | Copper wire coated blue that also connects to the cable in the wall and completes the circuit. In contrast, the earth wire doesn’t complete the circuit. |
Without the earth wire, if a fault occurs and the live wire becomes loose, it could touch the outer casing of the electrical appliance. The next person who uses the appliance could get electrocuted.
The earth wire is therefore connected to the outer case and is attached to a metal plate or water pipe underground. As the wire is made of copper, the earth wire provides a low resistance path to the ground. In the event of a fault, the large live current passing through the case earth wire will follow this path to the ground instead of passing through a person [standing on wet ground without insulating shoes], and will blow the fuse rendering the appliance safe.
Some appliances, such as vacuum cleaners and electric drills, do not have an earth wire. This is because they have plastic casings, or they have been designed so that the live wire cannot touch the casing. As a result, the casing cannot give an electric shock, even if the wires inside become loose.