UK Cable Colours
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The UK harmonised its fixed-wiring colours in the mid-2000s: single-phase line went from red to brown, neutral from black to blue, and three-phase became brown, black and grey where red, yellow and blue once ran. The protective conductor stays green-and-yellow.
The catch is that millions of installations pre-date the change, so a working electrician reads both systems fluently — and treats a black conductor with suspicion until proven, because in the old scheme it was neutral and in the new scheme it's a phase.
Quick-fire colour questions are one of the easiest wins in any electrical exam, and one of the most dangerous things to guess at on site.
This guide is free to read. There is no public quiz specifically for this topic yet. Explore the key terms below without leaving the page.
Common questions
- Can I try UK Cable Colours free on this page?
- This guide is free to read, but there is no public quiz specifically for this topic on this page. Browse public practice samples for other subjects, or create an account for the learning path. This course section is free with an account.
- What colour is the live wire in the UK?
- In fixed wiring installed since the harmonised colours arrived, line is brown, neutral is blue and the protective conductor is green-and-yellow. Older installations use red for line and black for neutral — which is why identification and testing, not colour alone, proves what a conductor is.
- What are the UK three-phase colours?
- Modern three-phase conductors are brown, black and grey with a blue neutral. The older scheme used red, yellow and blue phases with a black neutral — so black means a phase in one era and neutral in the other. Prove before you touch.
Explore key terms
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CPCCircuit Protective Conductor
The earth wire of a circuit. It links the metal parts of the equipment the circuit feeds back to the main earthing terminal. Normally it carries no current; if a fault makes that metalwork live, it carries the fault current so the fuse or breaker switches off. In UK wiring it is green and yellow, or bare inside twin-and-earth cable, with green-and-yellow sleeving wherever it is exposed.
Read the full CPC glossary entryPolarity
Verification that conductors are connected the right way round throughout an installation. Single-pole switches and protective devices must sit in the line conductor, the centre contact of screw lampholders on line, and socket terminals wired as marked. A polarity fault can leave equipment live when switched off — which is why it is checked dead and confirmed again live.
Read the full Polarity glossary entryConsumer unit
The distribution board of a domestic installation. A main switch, residual-current protection and a row of circuit devices on a DIN rail split the incoming supply into individually protected final circuits. Modern UK consumer units sit in non-combustible enclosures and increasingly give every circuit its own RCBO instead of sharing RCDs across banks.
Read the full Consumer unit glossary entry