Mains Electricity
4 marks · EasyA fan heater is rated at 2000 W and is connected to a 230 V mains supply. The heater has a plastic casing, with no earth wire.
Calculate the current used by the heater.
Explain why this appliance does not need an earth wire.
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) 8.7 A · must show Substitute values into P = IV, Correct calculation
(b) The heater has a plastic casing and uses double insulation, so the user cannot touch any electrical parts. Therefore, it does not need an earth wire. · must show Plastic casing/double insulation, No risk of touching live part
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Substitutes P and V correctly into formula P = IV or rearranges to I = P/V.
A1 (a) · 1 mark · Accurate final answer: 8.7 A (accept rounding within tolerance)
B1 (b) · 1 mark · States that the appliance is double insulated or has a plastic casing.
B2 (b) · 1 mark · Explains that electrical parts cannot be touched or there is no risk of shock from the casing.
Worked solution
(a) P = IV. So I = P / V = 2000 W / 230 V = 8.7 A.
(b) The heater has a plastic casing and is double insulated, so there is no metal casing that could become live. The user cannot touch live parts, so an earth wire is not needed.