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 |