Lesson 8 · Lighting Control

Four-Way Switches

Control one light from three or more locations by adding crossover switches between two 3-ways.

Beyond two locations

Two 3-way switches max out at two control locations. To control one light from three or more spots, you insert 4-way switches into the traveler wires between the two 3-ways. Each 4-way you add gives you one more control location.

What a 4-way does

A 4-way is a crossover switch. It has two inputs and two outputs, and it does one of two things: pass the travelers straight through (in→out, in→out), or cross them over (in→the other out). Flipping it swaps the traveler path, which — just like flipping a 3-way — makes or breaks the complete circuit.

A 4-way switch sits between two 3-ways. It either passes the travelers straight through or crosses them — adding a third control location. Add more 4-ways for more locations.

The pattern: always a 3-way on each end, with any number of 4-ways sandwiched in the travelers between them. Two 3-ways = 2 locations; add one 4-way = 3 locations; add another = 4; and so on.

Reading it

Trace the travelers through each switch. A 3-way picks which traveler it's on; a 4-way either keeps the travelers as-is or swaps them. The light is on when the path stays continuous end to end. Any single switch — 3-way or 4-way — flips that continuity, so any location can toggle the light.

What to take away

4-way switches are crossover switches placed between two 3-ways to add control locations. Straight-through or crossed — that's all a 4-way does, and it's enough to let a third (or fourth, or fifth) spot control the same light.

Now build it yourself

In the Sandbox, build the 3-way circuit from the last lesson, then insert a 4-Way Switch into the two travelers between the 3-ways. Now three switches all toggle the same light.

Open the Sandbox →