1. Difference appliances are earthed in different ways.
a) In a kettle the earth wire is connected to the metal casing. If the metal case was to become live, the earth wire and fuse would prevent someone using the kettle from receiving an electric shock. Explain why.
b) Why does an appliance that’s double insulated not require an earth wire?

2. A mains electricity cable tends to contain three cables.
a) Complete the table below.

b) The wire connects to the plug. The plug contains a fuse. What’s the purpose of the fuse?
c) An appliance works at 5A. What would be the best fuse to use?
3A
5A
13A
d) Explain your answer to c)

3. Most electrical appliances have their power and voltage of the connecting power supply printed on them.
a) An electric heater is connected to the mains supply which works at 230 V. It draws a current of 4 A. What’s the power of the electric heater?
b) An electric kettle has a 2500 W and is connected to the main supply. What fuse should be fitted to its plug?

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ANSWERS

1. a) The current flow through the live wire to the earth wire which causes the fuse to melt.

b) It’s not possible for the casing to come into contact with the live wire. This means that even if the wires were to come loose you wouldn’t get an electric shock from touching the appliance.

2. a)

b) To protect both an appliance and the electrical circuit.
c) iii) 13
d) 3A and 5A would cause the fuse to break too soon.

3. a) 230 x 4 = 920W

b) 2500 / 230 = 10.9A so a 13A fuse should be fitted.