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Mains electricity and the plug
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Homes in the UK use alternating current from the mains. The three-pin plug and fuses keep us safe.
a.c. and d.c.
Direct current (d.c.) flows in one direction only, e.g. from a battery.
Alternating current (a.c.) keeps changing direction.
UK mains is a.c. at about 230 V and 50 Hz.
Alternating current (a.c.) keeps changing direction.
UK mains is a.c. at about 230 V and 50 Hz.
The three-pin plug
Fuses and circuit breakers
If a fault makes a large current flow, the fuse melts and breaks the circuit in the live wire.
A circuit breaker switches off automatically and can be reset.
The live wire is dangerous even when a switch is off, because it is still at a high p.d. relative to earth.
A circuit breaker switches off automatically and can be reset.
The live wire is dangerous even when a switch is off, because it is still at a high p.d. relative to earth.
A 920 W toaster runs on 230 V mains. Which fuse should it have: 3 A, 5 A or 13 A?
- I = P ÷ V = 920 ÷ 230 = 4 A
- Choose the fuse just above the normal current
Answer: 5 A
UK mains is a.c., about 230 V and 50 Hz. Live is brown, neutral blue, earth green and yellow. Fuses and the earth wire protect people from faults.
The interactive lesson includes the diagrams for this topic.
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