A toaster has a metal casing and is connected to the mains supply using a three-core cable. Explain how the live, neutral, and earth wires each function during normal and fault conditions.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A toaster operates at 230 V from the UK mains supply. It has a metal outer casing and is plugged into a wall socket using a three-core cable containing live, neutral, and earth wires.
Model answer (4 marks)
1. The live wire carries the 230 V alternating current to the toaster.
2. The neutral wire completes the circuit, carrying the return current and is at 0 V.
3. The earth wire is bonded to the metal casing; if the live contacts the casing, a large fault current flows through earth.
4. The fault current causes the fuse to melt or the circuit breaker to trip, disconnecting the appliance and making it safe.
2. The neutral wire completes the circuit, carrying the return current and is at 0 V.
3. The earth wire is bonded to the metal casing; if the live contacts the casing, a large fault current flows through earth.
4. The fault current causes the fuse to melt or the circuit breaker to trip, disconnecting the appliance and making it safe.
Examiner tips
- Use the exact terms ‘live’, ‘neutral’, ‘earth’, ‘fuse’, ‘circuit breaker’. Show the sequence: live → appliance → neutral, and fault: live → casing → earth → protective device. Include the safety outcome (disconnection).
Common mistakes
- Confusing neutral with earth, or saying earth carries normal current. Omitting the protective device (fuse/circuit breaker) in the fault explanation.
Mark scheme (4 marks)
- The live wire carries the alternating current / voltage (at 230 V) to the toaster
- The neutral wire completes the circuit / carries current back (and is at 0 V)
- The earth wire is connected to the metal casing so that if a fault occurs / the live wire touches the casing, a large current flows
- The large fault current causes the fuse to melt / blow / the circuit breaker to trip, disconnecting the appliance and making it safe
Key terms in this question
Related
- All Eduqas GCSE Physics revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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