Two-way light switching: how to control one light from two places

To control one light from two places you use two two-way switches (single-pole changeover switches). The line goes to the common terminal of the first switch, two strapper wires run between the switches, and the common terminal of the second switch feeds the lamp. Neutral and earth go straight to the light, never through the switches.

Two-way light switch wiring diagram (control a light from two places)

For 230/400 V installations to IEC standards (Europe, UK and most of the world). North America uses different voltages, colours and rules: see the “Around the world” notes.

How it works

A two-way switch does not simply switch on and off: it changes the line over between two strapper wires. Two of these switches connected by a pair of strappers form a circuit where flipping either switch changes the state of the lamp.

Two-way switching diagram: line to the common of switch 1, two strappers between the switches, common of switch 2 to the lamp, N and PE straight to the lamp — Core colours as in a real installation: line brown, N blue, PE green-yellow, strappers black and grey.

What goes where

Section	Conductors
Board → box → switch 1 (common)	line L (N and PE continue to the lamp)
Switch 1 ↔ switch 2	2 strappers
Switch 2 (common) → lamp	switched line
Box → lamp	N and PE directly

Between the switches you need two strapper cores. Use a cable whose cores carry line colours (for example black and grey), not an ordinary brown, blue and green-yellow cable: see the box below.

Mind the colours: if you run an ordinary three-core cable coloured brown, blue and green-yellow between the switches, the switched line ends up on a blue or green-yellow core. It works electrically, but it breaks the rules. A green-yellow core may only ever be protective earth, never a strapper, even with a sleeve. Use a cable whose spare cores are black and grey. See wire colours.

Common mistakes

Neutral taken to a switch: switches only switch the line.
Common terminal mixed up with a strapper terminal: the light works "backwards" or only in one combination.
No earth at a metal light fitting.

More than two places

A third and every further switching point is added with an intermediate switch wired into the strappers: see intermediate switching. For four or more points, an impulse relay with push buttons is often simpler.

Around the world:
• UK: called two-way switching; switch terminals are usually marked COM, L1, L2. UK three-core and earth cable has brown, black and grey cores, which fits strappers nicely.
• USA: the same circuit is called a 3-way switch, the strappers are travelers, and the colours follow the NEC.
• Germany: Wechselschaltung.

Important: work only with the circuit isolated at the board and proven dead. Turning the light off at the switch is not enough.