2-Core vs 3-Core T&E — When & Why
Most domestic wiring uses 2-core + earth T&E (brown, blue, bare earth). But some jobs require 3-core + earth T&E, which adds a grey conductor.
When You Need 3-Core
You need 3-core T&E for:
- 2-way switching — the strapping wire between two 2-gang switches requires three conductors (L1, L2, and the common)
- Intermediate switching — connecting an intermediate switch between two 2-gang switches
The Grey Conductor
In 3-core T&E the grey conductor is normally used as a switch strapping wire. Because grey looks like a neutral, any grey conductor used in a live role must be sleeved brown at both ends.
What Goes Where
| Conductor | Normal role | Sleeving required? |
|---|---|---|
| Brown | Line (live) | No |
| Blue | Neutral | Only if used as live (sleeve brown) |
| Grey | Switch strapping | Yes — sleeve brown at both ends |
| Earth | CPC | Green/yellow sleeve at terminals |