UK Cable Colours
Sparks Basics · Free section
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.
Common questions
- Is there a free UK Cable Colours quiz?
- Yes. UK Cable Colours is taught in the Sparks Basics section of TradeTraining, which is free — you can practise in your browser without paying anything.
- 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.