3-way switch wiring diagram

Light: on

Toggle either switch to change its position and watch the light and the energized path change with it. Tap a conductor to replay the current path. The copper highlight is the live path, not a wire colour.

A 3-way circuit uses two switches to control one light from two places. Each switch is single-pole, double-throw: a single common terminal that connects to one of two travellers. The light is on whenever the two switches select the same traveller, so flipping either one changes the light.

How this circuit works

Follow the hot from the supply. It lands on the common of the first switch. From there it takes one of the two travellers across to the second switch, depending on which way that first switch is thrown. At the second switch, the common is the switched hot that feeds the lamp; the lamp's other side returns on the neutral.

So the whole question is: does the traveller the first switch chose line up with the traveller the second switch is listening to? If yes, there is an unbroken path from hot to lamp and the light is on. If no, the path dead-ends at an open blade and the light is off. That is why neither switch has a fixed "on" position — each one just changes which traveller is live, and the light follows whether the two agree.

Toggle the switches above and watch the copper trace. When the light is off, notice that the hot side is still energized right up to the open blade — the circuit is broken at the switch, not dead at the panel. That is the safety lesson the flat pictures never show you.

The other way to wire it

This diagram feeds the supply in at the first switch. The common alternative brings the supply and neutral to the light fixture and drops a switch loop to the switches. The switching topology is identical — two commons, two travellers — but the conductors carrying the supply and the neutral live in different places. Which arrangement is used, and the conductor colours that identify each one, are set by code, not by the circuit.

Questions people ask

Why is it called a 3-way switch if there are only two of them?

The name counts the terminals, not the switches. Each switch has three terminals — one common and two travellers — so the trade calls it a 3-way. You always use two of them to control one light from two places.

What are the traveller conductors?

The two conductors that run between the two switches. Each switch connects its common to one traveller or the other; when both switches happen to pick the same traveller, the circuit is complete and the light is on. Toggle either switch and it lands on the other traveller, breaking or making the path.

Why does either switch turn the light on or off?

Because neither switch has a fixed on or off position. The light state depends on whether the two switches agree on a traveller. Flipping one switch always changes that agreement, so it always flips the light — no matter what the other switch is doing.

Is there more than one way to wire a 3-way?

Yes. The common alternative feeds the supply in at the light fixture instead of at the first switch, and runs a switch loop down. The topology of the switching is the same — two commons, two travellers — but where the supply and neutral live changes. This diagram shows the supply-at-the-switch arrangement.

4-way switch wiring diagram — control a light from three or more places.
Glossary: traveller — the conductor that does the work here.
All wiring diagrams

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