The Three Wires Explained

Picture a metal kettle with a loose wire inside it, touching the metal body. Switched on, that body is now connected to the line. Anyone who picks it up gives the current a path through them to the floor. In a properly earthed kettle, the breaker trips the moment the fault happens. This lesson is about the wire that makes that happen, and its two companions.

In modern UK wiring, brown is line, blue is neutral and green-and-yellow is earth. Most homes still have some older wiring too, where line was red and neutral black, and a core can be re-labelled with coloured sleeving or tape to show it now does a different job. The diagram shows flat twin-and-earth, the usual cable in walls, with a bare earth core between the two insulated ones.

Colour tells you what job a wire was meant to do. It can’t tell you whether it was connected correctly, or whether it’s dead.