UK Cable Colour Codes
The 2006 harmonisation changed UK wiring colours. Knowing both the old and new schemes — and how to mark where they meet — keeps installations clear and safe.
UK wiring colours changed when the harmonised (European) colours were adopted, with a transition completing in 2006. Electricians routinely work on installations wired in either scheme, and sometimes both, so knowing each and how to identify conductors correctly is essential.
This guide sets out the current colours, the pre-2006 colours, three-phase identification, and how to handle installations where old and new wiring meet.
Key takeaways
- Current single-phase: brown line, blue neutral, green-and-yellow earth.
- Pre-2006 single-phase: red line, black neutral, green-and-yellow (or green) earth.
- Current three-phase: brown, black, grey lines; blue neutral.
- Pre-2006 three-phase: red, yellow, blue lines; black neutral.
- Where old and new colours meet, mark conductors clearly so the change of scheme is unmistakable.
Current colours
Since harmonisation, single-phase installations use brown for line, blue for neutral, and green-and-yellow for earth. This matches the colours used across Europe and is what all new work follows.
The green-and-yellow earth has been consistent for a long time and is the one colour that didn't change.
Pre-2006 colours
Older installations use red for line and black for neutral on single phase, with green-and-yellow (or, on very old work, plain green) for earth. This is the scheme you'll meet on any installation that hasn't been rewired since the mid-2000s.
The dangerous overlap is that black was neutral in the old scheme but is a line colour in the new three-phase scheme — a trap when old and new meet.
Watch the black conductor
Old black is neutral; new black is a line. Never assume — identify every conductor by testing where schemes could be mixed.
Three-phase identification
Current three-phase line colours are brown, black and grey, with a blue neutral. The pre-2006 scheme used red, yellow and blue for the lines with a black neutral.
Because blue was a line colour in the old scheme and is the neutral in the new one — and black flips between line and neutral — three-phase is where careful identification matters most.
Where old and new meet
When you extend or alter an installation wired in the old colours, mark the interface clearly. A warning notice stating that the installation has wiring colours to two versions of the standard is the usual approach, along with sleeving or labelling conductors so their function is unambiguous.
The goal is that the next person can't mistake an old neutral for a new line, or vice versa.
Frequently asked questions
What are the current UK wiring colours?
Brown for line, blue for neutral and green-and-yellow for earth on single phase. Three-phase lines are brown, black and grey with a blue neutral.
What were the old UK wiring colours?
Pre-2006 single phase used red line, black neutral and green-and-yellow earth. Three-phase used red, yellow and blue lines with a black neutral.
How do I mark mixed colours?
Put up a warning notice that the installation has cables to two versions of the colour standard, and sleeve or label conductors at the interface so their function is clear. Never rely on colour alone where schemes mix.
From guidance to action
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