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Protective conductors and cable coloursWhat is green and yellow allowed to be used for?
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Green/yellow = protective conductor. It's used only for:
- the earthing conductor
- main protective bonding conductors
- supplementary bonding conductors
- circuit protective conductors (CPCs)
The mix is 70% / 30% green and yellow, either way round. Never put green/yellow sleeving on a line or neutral.
| Colour | Use |
|---|---|
| Green/yellow | Protective conductor |
| Blue | Neutral |
| Brown | Line (L1 on three-phase) |
| Black | Line 2 (three-phase) |
| Grey | Line 3 (three-phase) |
- On single-phase, a blue, black or grey conductor used as a line must be sleeved brown at the terminations. For example, the blue of twin and earth used as a switch line gets brown sleeving. It's cheaper than buying twin brown cable.
- A neutral used as a mid-point or supply neutral must stay blue.
- Sleeve and terminate correctly as you go. Inspecting while you work saves problems when you test.
- UK colours changed in 2004 (from red/black). You'll still find old installations.
BS 7671 · Reg 514: identification of conductors · p.141 Electrician's Guide to the Building Regs · Chapter 11: identification of conductors, old and new colours Conductor ID comes up in the exam
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