Earthing
Without the earth wire, if a fault occurs and the live wire becomes loose, there is a danger that it will touch the metal case.
The next person who uses the appliance could get electrocuted.
The earth pin on the three pin plug is connected by a wire to the metal body of the appliance.
This wire is connected to earth via the plug socket 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 live current passing through the case will follow this path to the ground instead of passing through a person.
The earth wire has virtually no resistance and so large current flows.
This causes the fuse to blow, preventing any further current flow.
Key points
- The earth wire is a safety feature.
- The earth wire provides a low resistance path to earth.
- A large current flows in the earth wire which causes the fuse to melt, helping to protect the user from electric shock and the appliance from overheating and starting a fire.
- Current only flows in the earth wire when a fault occurs and the live wire touches the metal casing of the appliance.
