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Old and new cable coloursOld black, new black. Which one is live?
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The UK harmonised its colours with the rest of Europe (not because of Brexit). New colours could be used from 1 April 2004, and from 1 April 2006 only new-colour cable should be installed.
| Function | Old (pre-2004) | New (harmonised) |
|---|---|---|
| Line 1 / single-phase line | Red | Brown |
| Line 2 | Yellow | Black |
| Line 3 | Blue | Grey |
| Neutral | Black | Blue |
| Protective conductor | Green/yellow (unchanged) | |
Old black was neutral, but new black is a line (L2). Old blue was L3, but new blue is neutral. Mixing them up on an alteration can put a line in a neutral terminal, which is wrong polarity, or swap two lines, so a three-phase motor runs backwards and can be damaged. Always check what each conductor actually is before connecting.
Where old and new colours meet in one installation, a caution label has traditionally been fitted at the consumer unit: "This installation has wiring colours to two versions of BS 7671…". That requirement (Reg 514.14) was deleted in A2:2022, so the notice is no longer required by BS 7671 — though nothing stops you fitting one, especially on additions and alterations.
Colour-blind electricians aren't excluded. Apps can identify cable colours. Some rail and aviation roles do require a colour test.
Electrician's Guide to the Building Regs · Chapter 11 · old and new conductor colours table · p.191 On-Site Guide · Appendix K · identification of conductors (old and new)
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