Single-pole switches are typically a breeze. However, a lot of folks struggle with three-way switches, especially smart models. Master electrician Heath Eastman shows us exactly how to handle it, installing a smart new three-way switch to help control lighting in a stairway.
What is a 3-Way Switch?
A three-way switch refers to the type of switch used on a circuit where two individual switches control a light or device. They’re common in hallways, stairways, and other locations where controlling a device from two locations is convenient. They’re slightly trickier to install than a standard single-pole switch, but a DIYer can handle the job.
Three-way switches come in two variations: traditional and smart switches. A smart 3-way switch can actually be easier to install and give homeowners more control over their lighting.
What makes a three-way switch different from a standard single-pole is its internal wiring. A three-way switch has three connections: a common screw, which is always a darker color and carries power either into or out of the switch; two traveler screws, which are the same color (typically brass or silver) and allow the two switches to communicate with each other; and a ground. The traveler wires are what enable you to control the same light from two different locations—power literally travels back and forth between the switches.
Pro Tip: Heath, a This Old House electrician, notes that the switch to smart switches has generated a lot of homeowner confusion: “I’ve been getting a lot of phone calls from homeowners who are finding certain configurations a little bit confusing.” The single-pole switch is straightforward—one location, two screws, and a ground—but the three-way switch adds complexity with its additional terminals and traveler wires.
How to Install a 3-Way Smart Switch
- First, turn off the breaker controlling the switch. Operate both switches to ensure the power is off.
- Next, remove the wall plate, exposing the existing 3-way switch. Test the switches with a non-contact tester to ensure nothing is energized.
- Remove the switch from the box.
- There should be two brass screws and one black screw on the switch. The wire attached to the black screw is the common, and it should be marked so you can attach it to the common on the new switch. The other two wires are “travelers.”
- Once all of the wires are marked, cut them from the switch with wire cutters and strip back their jackets.
- Install the new switch by first attaching the green wire (the ground) to the bare copper wire with a wire nut. Then, attach the travelers to their corresponding wires (in our case, red to red, black to blue). Finally, connect the switch’s black wire to the common wire with a wire nut.
- Make sure all of the connections are secure and carefully tuck the wires back into the junction box before fastening the switch to the box and installing the cover plate.
- At the other switch, you can either install a smart remote, which simply requires connecting all of the wires together under one wire nut and programming it, or a mechanical switch to operate with the smart switch.
- If you opt for a mechanical switch, remove the existing switch from the box. Wire the red wire (or whichever traveler wire color you tied to the smart switch’s red wire) and the common under one wire nut before attaching it to the common screw with a jumper. Attach the other traveler wire to the other brass screw and leave one brass screw empty. Reinstall the switch in the box and the cover plate.
Why Keep the Mechanical Switch? While a smart remote at the second location offers a clean, wireless setup, there’s a practical reason many homeowners opt for the mechanical switch instead. As the This Old House team explained during the project: “In this situation, though, we want to keep the mechanical switch like we have. It’s just simpler to use when guests come in and out.” A traditional toggle is intuitive for anyone, no app or pairing required.
Materials
Tools
Resources
At the top of the stairs Heath installed: Lutron Diva Smart Dimmer Switch for Caseta Smart Lighting, 150-Watt LED.
At the bottom of the stairs Heath installed: Lutron Pico Smart Remote Wall Mounting Kit, for Caseta Smart Dimmer Switch 3-Way Applications.
Switch manufacturer: Lutron
Pro Tip: Heath notes that the Pico remote can be mounted with a wall plate to make it look like a conventional wall switch — no wiring or wall cutting required. Additionally, adding the Lutron smart hub gives you control of the system from your phone or tablet, letting you group switches together, set timers, and schedule lighting events throughout the house.
