3-Way Switch Wiring: A How to Comprehensive Guide

What is a Three-Way Switch?

A single pole switch controls a light from one location only. 

A three-way switch controls a light fixture from two different locations. 

In the image above you can see a single pole switch has three screws while the 3-way switch has four screws. That’s for a “traveler wire” which is used in wiring 3-way switches. Another interesting note is that 3-way switches aren’t labeled “ON/OFF” like single pole switches.

It provides flexibility, convenience, and safety. We use a three-way switch to control the ceiling lights in the cabin loft. We can turn on the loft lights from a switch on the main floor, go up the ladder to the loft and then turn them off from a second switch upstairs.  

EngineeringEscape did a great job of explaining how a 3-way switch works. 

Here’s a short animation of how a 3-way switch works by Terry Peterman.

Before diving into the wiring process, gather the necessary tools: 

• Three-way switch
• 14-3 or 12-3 cable (14-4 if required)
• Screwdriver (flathead and Philips)
• Wire stripper
• Voltage probe or Voltmeter
• Needle-nose pliers
• Wire nuts
• Electrical tape

We also have a complete list of the tools we use here at the off grid cabin.

Now, let’s dive into the actual process of wiring a three-way switch. 

Depending on which one gets the power first, the light switch (which is more usual) or the light fixture, you’ll follow one of the following diagrams for 3-way switch wiring.

Turn Off the Power

Safety first! Ensure the power is turned off at the breaker before you start working on the wiring. 

Always use a voltage tester to double-check and make certain the light switch has no power going to it.

Identify the Wires

Differentiate the different wires in the 14-3 NM cable to avoid confusion. Typically, you’ll encounter three insulated wires (Black, Red, White) and a bare Copper ground wire.

This is the wiring you will need when connecting from the power source to a three-way switch, to a second three-way switch and finally to the light. 

In our first diagram the power source is coming to the light switch.

• In this diagram, the incoming hot wire is attached to the first switch’s common dark-colored terminal.
• The two hot wires of the three-wire cable connect to a pair of brass-colored traveler terminals on each switch.
• The fixture’s hot wire connects to the second switch’s common terminal.

In our next two scenarios you’ll need 14-4 wire. This wire includes an extra wire (blue)  to act as a second traveler. 

This 3-way light switch wiring diagram shows how to wire the switch and the light when power is coming to the light fixture. Here, the power source is first connected to the light fixture and then to the three-way switches.

• The black hot wire connects to the far right switch’s common terminal.
• Red and blue wires link the traveler terminals of both switches.
• The red wire, which is connected to the first switch’s common terminal, leads back to the fixture.

Here the light fixture is in between the three-way switches and again requires 14-4 wire that has the second traveler wire. 

• The incoming black hot wire is connected to the right switch’s common terminal.
• Two lengths of four-wire with ground cable, joined at the fixture box, link the right and left switch traveler terminals to each other and to the fixture.

Mount the Switch

Carefully mount the switch back into the electrical box, ensuring a secure fit. 

There are opposing thoughts about wrapping the switch with electrical tape before placing the switch back into the electrical box. Personally I do wrap my switches and outlets with electrical tape. I’ll leave that up to you to decide whether or not you want to do it. For reference I use 3M vinyl electrical tape that won’t dry out and/or peel off when used properly. 

To wrap the switch/outlet I apply one full wrap without stretching the tape and a second wrap slightly pulling/stretching the tape. Then, finally make sure to cut the tape and not pull it. The local box stores actually sell a product called ArmourBand Insulating Straps for this exact purpose. 

Test the Wiring

Lastly, turn the power back on and test your newly wired three-way switch to ensure it operates correctly.

Increased Convenience

• They offer convenience and safety, as you can turn on or off the light without having to walk across a dark or long space.

Save Energy

• They can save energy and money, as you can avoid leaving the light on unnecessarily when you leave a room.

Smart Devices

• They can work with smart devices and voice assistants, giving you more options to control your lighting remotely or with voice commands.

Security 

• They can integrate with security systems and motion sensors, enhancing the protection of your home and automatically turning on or off the light when needed.

Wiring a three-way switch might seem complex initially, but with our comprehensive guide, you can tackle it with confidence. Remember, safety is paramount, so always double check wires before you touch anything with a functioning voltmeter or voltage tester. If in doubt, call a professional. 

We have a complete section dedicated to the design and construction of our cabin here. You can go all the way back to when we first built the foundation, framed the walls, and constructed the roof right up to installing our composting toilet and hot water heater.

Let us know in the comments below if you’ll be tackling any electrical work yourself and if you have experience, feel free to share any additional safety tips with our readers.

Can I use any color for traveler wires?

• While the industry standard is red and black for traveler wires, the color might vary. Always identify wires properly before proceeding.

Is it possible to add more than two switches to control a single light?

• Yes, it is. You can use additional four-way switches in conjunction with three-way switches for more control points.

Are there wireless alternatives to three-way switches?

• Certainly! Smart home technology offers wireless solutions for remote control of lights without additional wiring. We use several smart light switches and smart bulbs here at the off grid cabin. 

What if I have multiple lights controlled by a three-way switch?

• You will need to extend the wiring to additional light fixtures while maintaining the three-way switch configuration in the wiring diagram(s) above.

Can I wire a three-way switch without a ground wire?

• While it’s not advisable, it’s possible in some cases. However, for safety reasons, a ground wire is always recommended.