Electrical Safety
Physics: Edexcel IGCSE, topic 2.1.5
Electrical Safety: Earthing and Insulating Metal Cases
Metals conduct electricity, so metal cases may need earthing or insulating to stop them giving us electric shocks.
Metal cases
- Lots of electrical appliances, such as toasters and microwave ovens, have metal casings.
- If there is a fault in the appliance, one of the wires may touch the metal case. Metals conduct electricity, so anyone touching the case could then receive an electric shock.
Earth wire
- An earth wire is a low resistance wire that connects the metal case to the ground.
- If the casing is touched by a wire inside the appliance, the current will flow through the earth wire.
- Because the resistance of the earth wire is low, a very high current will flow through it, breaking the fuse in the device. This will stop the flow of current and make the appliance safe.
Plastic insulation
- Many appliances are made with plastic cases.
- Plastic is an insulator, so the case provides an extra layer of insulation. The appliance is then said to be double insulated.
- The symbol for double insulated is shown in the diagram.
- Double insulated appliances do not need an Earth connection.
Test yourself on Electrical Safety
What is the purpose of an earth wire?
Earth wires are needed for appliances with what?