Explain why the insulation around the three wires in a mains plug is colour coded.

AQA GCSE Physics (8463) — 4.2.3 Domestic uses and safety · Explain · 4 marks · View as Markdown

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

A student is wiring a new mains plug for a kitchen appliance. The plug contains a live wire, a neutral wire, and an earth wire.

Model answer (4 marks)

The insulation is colour coded to allow quick and correct identification of each conductor. The live wire is brown, the neutral is blue, and the earth is green with yellow stripes. This coding ensures that the live, neutral and earth are connected to the correct terminals in the plug and the appliance. If a wire is connected to the wrong terminal, the appliance could become live or the user could be exposed to a shock, which is dangerous.

Examiner tips

Use the exact colour names (brown, blue, green/yellow) as the scheme recognises them.
Show that the coding prevents mis‑connection and the resulting danger.
Mention the safety benefit of easy identification during installation.

Common mistakes

Confusing the colours of live and neutral (e.g. saying live is blue).
Omitting the earth wire colour or its importance.
Failing to link the colour coding to the risk of electrocution.

Mark scheme (4 marks)

Correct colour identified for live wire (brown)
Correct colour identified for neutral wire (blue) and/or earth wire (green and yellow stripes)
Colour coding allows easy/correct identification of each wire
Connecting the wrong wire to the wrong terminal would be dangerous / could result in electrocution or the appliance becoming live

Key terms in this question

insulation · mains