GCSE Physics · Edexcel 1PH0 · Topic 10D
Mains electricity and safety
Key points
- Direct current (d.c.) flows one way (cells, batteries). Alternating current (a.c.) keeps reversing direction.
- UK mains is a.c. at about 230 V and 50 Hz.
- Three-core cable: live (brown, at 230 V), neutral (blue, near 0 V), earth (green and yellow, a safety wire).
- A fuse in the live wire melts if the current is too high, breaking the circuit. Choose a fuse rating just above the normal current.
- If a fault makes a metal case live, the earth wire carries a large current to earth, blowing the fuse. Double-insulated appliances need no earth.
- Touching the live wire is dangerous because there is a large pd between it and your body (at 0 V), so current passes through you. Circuit breakers switch off faster than fuses.
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Mains electricity can kill, so it is delivered with several layers of protection. This sub-topic explains how mains supply differs from a battery, what each wire in a plug does, and how fuses, circuit breakers and earthing keep you safe.
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