How to Wire a Three-Way Light Switch

Introduction

Wiring a three-way light switch allows you to control a light fixture from two separate locations, like the top and bottom of a staircase. While it may seem daunting, installing a three-way switch is not much more difficult than wiring a standard single-pole switch. By following some basic wiring principles and safety precautions, you can successfully wire your three-way switch.

What You Will Need

Before beginning, make sure you have the following materials:

• Two three-way switches - You will need a pair of matched three-way switches. These have three terminals - a common terminal and two travelers.

• Electrical box - You will need a box to mount each three-way switch. Make sure they are large enough.

• NM cable - Use 14/2 cable with black, white, and ground wires. NM stands for nonmetallic sheathed cable.

• Wire connectors - Get twist-on wire connectors rated for the gauge of wire you are using.

• Wire strippers - A wire stripper makes quick work of stripping insulation.

• Voltage tester - Essential for testing wires are not live before working on them.

• Phillips screwdriver - For mounting the switches and connecting wires.

• Pliers - Used for bending and cutting the cable.

How a Three-Way Switch Works

Before wiring, it helps to understand how a three-way switch operates. A three-way switch has three terminals:

• Common terminal
• Traveler 1 terminal
• Traveler 2 terminal

Power flows from the common terminal through one traveler terminal to the light fixture. The traveler terminals alternate which one receives power when you flip the switch. The common terminal remains constant.

One three-way switch will have the common terminal wired to the hot source. The other three-way will have the common terminal wired to the light fixture. The traveler wires connect between the pair of switches.

This allows flipping either switch to control the light fixture, because power can flow through two possible paths using one traveler or the other.

Step-by-Step Wiring

Follow these steps to wire a three-way light switch:

1. Turn Off Power

The first step is to turn off power to the circuit you are working on at the main breaker panel. Verify power is off using a voltage tester on the wires inside the electrical box before touching them.

2. Install First Three-Way Switch

• Mount one three-way switch in an electrical box and secure it in place.
• Connect the hot source wire to the common terminal.
• Connect the hot wire going to the light fixture to one of the traveler terminals. It does not matter which one. Use a twist-on wire connector to make the connections.
• Connect all ground wires together using a wire connector if the box is metal.

3. Install Second Three-Way Switch

• Mount the second three-way switch in its electrical box down the circuit.
• Connect the traveler wire coming from the first switch to one of the traveler terminals on the second switch.
• Connect the wire headed to the light fixture to the common terminal on the second switch.
• Connect all ground wires if box is metal.

4. Connect Traveler Wires

• Run a two-wire NM cable between the boxes with the existing wires.
• Connect one wire from the new cable to the remaining traveler terminal on each switch.
• These wires connecting between switches allow the switches to communicate.

5. Test Operation & Install Covers

• Carefully turn the power back on at the panel.
• Use a voltage tester to verify that power is running to the common terminal on the first switch.
• Test flipping each switch to ensure proper operation and that the light turns on and off from both locations.
• Install switch and wall plates once operation is confirmed.

Three-Way Switch Wiring Diagram

Use this diagram as a visual reference for wiring two three-way switches:

The power source and light fixture are at opposite ends, with a three-wire NM cable running between the switches. The traveler wires allow the switches to communicate to control the light.

Conclusion

Installing three-way light switches is a great DIY home wiring project. Make sure to take proper safety precautions like turning off power at the breaker before beginning work. Following basic wiring principles allows you to wire three-way switches to control lights from multiple locations. Take it slow and double-check your switch wiring before restoring power.