Explain why household electrical appliances are connected to the earth wire and why fuses are used in electrical circuits.

Eduqas GCSE Physics — 7.4 Domestic uses and safety · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Most household appliances are fitted with a three-pin plug containing a live wire, a neutral wire, and an earth wire. A fuse is also included in the circuit.

Model answer (4 marks)

The earth wire connects the metal casing of the appliance to earth (ground). If a fault occurs and the live wire touches the metal casing, the current flows safely to earth rather than through a person touching the casing. When a fault causes a large current to flow, the fuse wire melts / blows. This breaks the circuit, preventing overheating, fire or further damage to the appliance.

Examiner tips

Use the exact terms ‘earth wire’, ‘metal casing’, ‘current flows to earth’, ‘fuse melts’, ‘breaks the circuit’.
Show the cause–effect chain: fault → live touches casing → earth provides low‑resistance path → fuse blows → circuit opens.
Keep the answer concise – 4 points, one sentence each.

Common mistakes

Confusing the earth wire with the neutral wire.
Saying the fuse protects the appliance but not the person or the circuit.
Using vague terms like ‘protects’ without explaining how the fuse works.

Mark scheme (4 marks)

The earth wire connects the metal casing of the appliance to earth (ground)
If a fault occurs and the live wire touches the metal casing, the current flows safely to earth rather than through a person touching the casing
When a fault causes a large current to flow, the fuse wire melts / blows
This breaks the circuit, preventing overheating / fire / further damage to the appliance

Key terms in this question

earth wire · fuse · circuit