Safety devices
2 marks · EasyLook at the diagram of a simple mains circuit with a lamp, fuse, and earth wire.
Explain why the earth wire is connected to metal casings.
State what would happen if the live wire inside the appliance touched the metal casing.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) To provide a low-resistance path for current in case of a fault, protecting the user from electric shock.
(b) A large current flows to earth, blowing the fuse and disconnecting the appliance.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Explains earth wire protects by providing path for fault current/shock prevention.
B1 (b) · 1 mark · States fuse blows/disconnects if live wire contacts casing.
Worked solution
a) The earth wire is attached to the metal casing to safely carry any fault current away, stopping electric shock.
b) If the live wire touched the casing, current would flow to earth, causing the fuse to blow and turning off the power.