How to Wire a Three-Way Switch

How to Wire a Three-Way Switch


Wiring a three-way switch allows you to control a light fixture or other device from two separate locations. For example, you might have a light at the top and bottom of a staircase that you want to be able to turn on or off from either location. Three-way switches require a bit more wiring than a standard single-pole switch, but the job can be easily accomplished by the average do-it-yourselfer with some basic electrical knowledge. In this guide, I'll walk you through the complete process of wiring a three-way switch step-by-step.

What You'll Need

Before getting started, make sure you have the following materials:

How a 3-Way Switch Works

Before jumping into the wiring, it helps to understand how a three-way switch works.

A three-way switch has three terminal screws - the common (COM or black screw), the traveler (red screw), and the ground (green screw). The common terminal is connected to the hot power source. The traveler terminals allow the switches to communicate and alternate turning the light on and off.

The key thing to understand is that the switches don't directly control the light. Instead, they switch the traveler wires on and off which alternates the power flow to the light.

Step-by-Step Installation

With the materials gathered and a basic understanding of how three-way switches work, you're ready to install them. I'll go through each step of the process in detail:

1. Turn Off Power

The first step is to turn off power to the circuit at the main breaker panel. Verify power is off by using a non-contact voltage tester. Working with live wiring can result in a nasty shock!

2. Install Switch Boxes

Install a box for each three-way switch following standard electrical box mounting procedures. One box will contain the "line" switch that connects to the hot power source. The other box houses the "load" switch that connects to the light fixture.

3. Run Cables

Run cables between the two switch boxes and to the light fixture. You'll need 3-wire NM-B cables with a black, red, white and ground wire. The black and red wires serve as the travelers.

4. Connect Switches and Lights

With the cables run, you can now connect the switches. Follow these steps carefully:

The ground wires are all connected at each box for safety.

5. Install Switches and Test

With all wires securely connected, install the switches in their boxes and secure them with the included screws. Turn the power back on and test that the switches work to control the lights!

Three-Way Switch Wiring Diagram

Here is a wiring diagram that summarizes the key connections for installing a pair of three-way switches to control a light fixture:

Three-way switch wiring diagram


Installing three-way switches is more involved than standard single-pole switches but certainly doable for the dedicated DIYer. The key is understanding how the travelers operate between the pair of switches. Take it step-by-step and double-check all connections before turning the power back on. With a little care, you'll have three-way control wired up in no time!