A washing machine has a metal casing and is connected to the mains electricity supply using a three-core cable. The three-core cable contains a live wire, a neutral wire, and an earth wire. Explain how the earth wire protects a user from electric shock if a fault develops inside the washing machine.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A washing machine has a metal casing and is connected to the mains electricity supply using a three-core cable containing a live wire, a neutral wire, and an earth wire.
Model answer (4 marks)
If a fault occurs, the live wire may touch the metal casing, making it live and allowing current to flow into the casing. The earth wire gives a low‑resistance path for this fault current to flow safely to earth. The large surge of current through the earth wire causes the fuse to melt or the circuit breaker to trip, breaking the circuit. Once the circuit is disconnected, the appliance is no longer connected to the mains and the user cannot receive an electric shock by touching the casing.
Examiner tips
- Use the word "fault" and explain the live wire contacting the casing.
- Mention the earth wire provides a low‑resistance path and that the fuse/circuit breaker reacts to the surge.
Common mistakes
- Failing to state that the earth wire gives a low‑resistance path.
- Not mentioning the fuse or circuit breaker tripping as the protective action.
Mark scheme (4 marks)
- If a fault occurs, the live wire may come into contact with the metal casing, making it live / causing current to flow into the casing.
- The earth wire provides a low resistance path for the current to flow safely to earth / ground.
- The large surge of current through the earth wire causes the fuse to melt / the circuit breaker to trip, breaking the circuit.
- This disconnects the appliance from the mains supply, so the user cannot receive an electric shock by touching the casing.
Key terms in this question
earth wire · live wire · mains electricity
Related
- All Pearson Edexcel International GCSE Physics (4PH1) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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