These diagrams illustrate how to wire a pair of three-way light switches in three different situations.
Three-way light switches control a light from two locations, such as from both ends of a staircase or hallway.
A three-way switch is built and wired a little differently than a conventional single-pole light switch. For starters, it doesn’t have “OFF” and “ON” printed on the toggle, and it doesn’t have a top and bottom. It also has one more terminal. Rather than having two terminal screws and a ground screw like a regular (“single-pole”) light switch, a three-way switch has three terminal screws and a ground screw.
Note: Many contemporary switches have holes for plugging-in the wires instead of screws that lock the wires in place. Nevertheless, the principle is the same.
On most 3-way switches, two of the terminals are the same color (typically silver or brass), and the third terminal, called a “common terminal,” is a different, often darker, color.
Not all three-way switches have these terminals placed in the same configuration, so you have to pay attention to their colors (and the instructions that come with the package) when wiring them.
The switch shown here has silver and gold screws opposite one another and a bronze screw in the third position. The green screw at one end is for the ground wire.
When replacing an existing three-way light switch, be sure to return the wires to the proper screw terminals. Put a piece of tape on the wire that goes to the common terminal screw. The other two wires can attach to either of the identical terminals.
Refer to the illustrations below for doing the rough-in wiring for each of these situations.
Note that these diagrams assume that you’re following all recommended practices for safe installation of electrical circuits.
Always turn off the power to the circuit before working with exposed wires.
It’s important to recognize that a light switch is designed to interrupt the “hot” wire when it’s turned off.
With this in mind, the white wire from the power source always goes uninterrupted to the light fixture and the bare grounding wires are always fastened to grounding screws. But the “hot” or “charged” wire coming from the power source is routed through the switches.
With a three-way switch, three wires connect the pair of switches—two black “traveler” wires and a third “common” wire.
When the circuit’s power is turned on, any of these may be “hot,” depending upon how the switches are toggled.
Because “3-wire-with-ground” nonmetallic electrical cable such as Romex is often used to wire switches, a slight modification is often made during installation. This type of cable contains a white wire that needs to serve as a black wire. For this reason, the white wire is painted or taped black to identify it as a black (hot) wire when the cable is used to connect two three-way switches and lights.
There are three basic ways three-way switches may be set up to control one or more lights. The right one for you will depend upon where the power enters the circuit (at one of the switches or at the light fixture), and the placement of the switches and lights.
Please note: All switches that have a green grounding screw or wire must be grounded to the metal electrical box or to the circuit’s bare or green ground wire.
A) The wires from the power source may enter one switch box first, then travel to the light, and then terminate at the other switch. Note in this illustration that the inbound white wire travels through the first switch box and terminates at the light fixture.
B) The wires from the power source may enter the light fixture box first, travel from there to one switch, and then connect that switch to the other switch. In this configuration, the inbound white wire connects directly to the light fixture. The black wire connects to a taped white wire that passes through the first switch box and connects to the common terminal on the second switch. Red and black travelers then connect the paired traveler terminals on both switches.
C) The wires from the power source go from switch to switch, and then go to the light. In this configuration, the power enters the first switch, and the light fixture is placed after the second switch.
The white wire, connected by wire nuts in each switch box, is continuous from the source to the light fixture. The charged black wire connects to the common terminal of the first switch and is then carried by paired travelers to the paired terminals of the second switch. The common terminal of the second switch sends the black wire to the light fixture.