Cable Types, Sizes & Colour Codes
The most common cable used in UK domestic wiring is Twin & Earth (T&E), also called flat grey cable. It contains three conductors in a flat grey sheath:
Cable Sizes
| Size | Used for | Typical MCB |
|---|---|---|
| 1mm² | Lighting circuits | 6A or 10A |
| 1.5mm² | Older radials, some spurs | 16A |
| 2.5mm² | Ring final, radial socket circuits | 32A (ring) / 20A (radial) |
A 32A ring circuit can use 2.5mm² because the ring gives two parallel paths back to the consumer unit — each half of the ring shares the load. On a radial (single-run) circuit, 2.5mm² can only be protected by a 20A MCB. Don't use a 32A MCB on a radial wired in 2.5mm².
3-Core T&E
For 2-way switching, you need 3-core T&E. This adds a grey conductor (used as the switch wire). Because grey is normally neutral, any grey conductor used in a live role must be identified with brown sleeving at both ends (a durable brown sleeve or ferrule — not adhesive tape, which can unwrap or slide off).
See 2-core vs 3-core T&E — when & why for more detail.