Electrical 101

How to Identify 3 and 4-Way Switch Wires

I replaced a 3 or 4-way switch and now the switches don’t work properly. Did I wire it wrong?

Conventional 3-way switch wiring is fairly simple. The common terminal of one switch connects to line voltage. The common terminal of the other switch connects to the load (light).

Two traveler wires connect to each 3-way switch. These wires are interchangeable with each other.

When replacing a 3-way switch, first mark the common wire with a small piece of tape. If the switch is removed without marking the common wire, and you lost track of the old connections, don’t worry.

One common wire

Two traveler wires

One common wire

Two traveler wires

Identify 3-Way Switch Wires for NM cable.

With NM cable, it is easy to identify the common and traveler wires inside an electrical box for each 3-way switch. After turning off power to each electrical box, remove the cover and pull out the switches.

- The pair of traveler wires on each switch go into the same NM cable in each of their switch boxes.

- The common wire of each switch goes to a different NM cable than the traveler’s wires.

Identify 4-Way Switch Wires for NM cable.

With NM cable, it is easy to identify the common and traveler wires inside an electrical box for each 4-way switch. After turning off power to each electrical box, remove the cover and pull out the switches.

- The pair of traveler wires on the top or bottom of each switch go into the same NM cable in their switch box.

- The other pair of traveler wires go into the same cable, but not the same NM cable as the other pair.

4-way switch diagram

3-way switch diagram

3-Way Switch Box