Three-way switches seem a little confusing, but we often make them out to be harder than they are. To prove it, master electrician Heath Eastman built a diagram to show host Kevin O’Connor just how they work, and how to wire one.
What is a Three-Way Switch?
A three-way switch is an electrical device that allows homeowners to control a single device or fixture from two different locations. They’re common in rooms with two entrances, hallways, stairways, and other similar settings. Unlike standard on/off switches, which simply open and close a circuit, three-way switches reroute the circuit along one of two traveling wires (travelers) between two separate switches, allowing users to turn the fixture on and off from either end.
How Do Three-Way Switches Work?
There are quite a few things to know about three-way switch systems, but they’re not as complicated as we often make them out to be.
They Need Special Wires
A standard switch requires a 2-wire cable with the neutral, hot, and ground. A three-way system requires a 3-wire cable to run between the two switches, including the neutral, two “travelers,” and the ground wire. The travelers are typically black and red, while the neutral remains white, though that isn’t always the case. The feed wire (the wire feeding from the panel) and the load wire (the wire feeding to the fixture) are standard two-wire cables.
They Use Special Switch Devices
The switches in a three-way system are also specific. While a traditional single-pole switch has two brass screws (which the black, or hot, wires attach to) and a green screw, three-way devices have two brass screws, one black screw, and one ground screw. The travelers (the black and red wires) are installed on the brass screws between the two switches. The feed (power from the panel) enters the first device on the black screw, exits the second device on its black screw, and continues to the fixture.
They Route Power Between the Travelers
The easiest way to understand how these switches work is simply that they reroute power. The power or line from the standard two-wire cable enters the device at the black screw, while the neutral continues unbroken to the device itself (it’s often wire-nutted in the electrical boxes). Inside the first switch, the power is routed to one of the brass screws and exits on one of the travelers, entering the second device.
If the second switch is toggled to the same screw, the power exits through the black screw, travels along the load wire, and powers the device. If the switch is toggled to the other screw, the power never leaves the switch, leaving the device off. However, flipping the switch on either side will align the two switches, allowing power to run through the first switch, along a traveler, into the second switch, and out to the device.
So What’s the Easiest Setup?
While Heath admits there are several ways to do it, he likes to keep it as simple as possible:
Run 14/2 cable from the panel to the first electrical box, 14/3 between the two switches’ electrical boxes, and then 14/2 from the second electrical box to the device.
Attach the hot from the 14/2 to the black screw on the first switch, tie the neutrals from the 14/3 together with a wire nut, and attach the ground wires to the ground screw with a pigtail.
Attach the black and red wires (the travelers) from the 14/3 cable to the brass screws on both switches (no ground wire is required between the two).
Attach the hot wire from the 14/2 cable between the second switch and device to the black screw, and tie the neutrals from the 14/3 and 14/2 together with a wire nut. Wire the ground to the green screw.
This is the easiest setup and makes the current routing simpler to understand.
