What Is a 3-Way Switch? Parts and Wiring - The Spruce

A three-way switch controls ceiling lights, fans, or other fixtures from two locations, unlike a single-pole switch, which controls a light fixture from a single location. You can arrange switches to control light fixtures from multiple locations using a three-way or four-way switch.

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Read on to learn when to use a three-way switch, how to identify it, and how to understand its wiring and different parts.

What Is a 3-Way Switch?

A three-way switch has three screw terminals on the body of the switch in addition to the green grounding screw. One screw, known as the common, is a darker color than the others. The other two screws, usually a lighter brass color, are known as the traveler terminals. 

The switch toggle does not have ON or OFF markings. Since this switch has no true ON or OFF position, the ON or OFF marking on the toggle is unnecessary and would be confusing.

When to Use a 3-Way Switch

Three-way switches are commonly used to control one light fixture from two locations. For example, a long hallway or stairway might use a three-way switch at each end so that lights can be turned on when approaching one end of the hall or stairway and then shut off from the other end.

How a 3-Way Switch Works

When both toggles are up or down, the circuit is complete, and the light fixture will be illuminated. The circuit is interrupted when the toggles are in opposite positions and the light fixture turns off. A three-way switch allows either switch to control the on-off function of the light fixture at any time.

Parts of a 3-Way Switch

A three-way switch has four different screw terminals on its body:

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• Grounding screw: The green screw attached to the metal strap of the switch is always for the ground wire (this is the bare copper or green insulated wire within the circuit). Grounding screws on switches were not always required, so if you are replacing an old three-way switch, you may find one without the grounding screw.
• Traveler screws (two): The two lighter, brass-colored screws are called the traveler screws. The travel wires connected to these screws will offer two different pathways for power to travel from one switch to the other.
• Common terminal screw: The last screw is the common terminal. It is darker than the travelers, usually dark brass, copper, or black. This screw serves one of two purposes depending on where it is positioned in the circuit run: Either it accepts the incoming black (hot) wire from the power source, or it connects to the black (hot) wire that leads onward to the light fixture.

The Grounding Screw Terminal

For safety, always install a three-way switch that has a grounding screw. It is connected directly to the metal strap of the switch, and it may be located on the bottom of the switch, as shown here, on the side, or in another location. If you run across an older switch without a grounding screw, it should be replaced with a newer, grounded switch. 

3-Way Switch Wiring

Three-way switches can be wired in various ways, depending on their location relative to the light fixture in the circuit cable run. For example, they can be arranged so that the feed cable runs to the first three-way switch, then to the light fixture box, and then to the second three-way switch. 

Here's an example of a configuration where the feeder circuit cable runs through two three-way switches on its way to the light fixture:

Connect the First 3-Way Switch

The feeder wire from the power source is a two-wire cable with a ground. It has a black hot wire, a white neutral wire, and a bare copper grounding wire.

• Connect the black feed wire to the common screw on the switch.
• Connect the grounding wire to the switch using a pigtail wire and the second cable run that continues to the next switch.
• If the switch box is metal, it also must be pigtailed to the grounding wires. 
• Switches do not have white-colored neutral wire connections, so the neutral wires at the switch boxes are joined together to pass through to the light fixture box. 

Run the Circuit Cable

The circuit cable that links the two switches is a three-wire cable. The black and red wires are "travelers." They connect to the traveler screw terminals on the two switches. This connection provides two alternate pathways for hot current to flow between the switches, allowing the switches to turn the lights on and off flexibly. 

Connect the Second 3-Way Switch

The wiring at the second switch box location is similar to that of the first switch, with the traveler terminals connected to the traveler wires coming from the first switch.

• Connect the black hot wire to the common screw terminal so it leads onward to the light fixture.
• Join the white neutral wires together.
• Join the grounding wires together with pigtail wire, which is connected to the switch and to the box (if it is metal). 

Run the Connection to the Light Fixture

The cable run from the light fixture requires a 2-wire cable with a grounding wire. 

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