How to Wire a 3-Way Light Switch or Dimmer

There are four topics on this page:

1) When do I need to use a 3-way light switch?

If you want to control a light fixture or receptacle from more than one location or switch, you will need to use a 3-way light switch. For example, to operate a light in a stairway from both levels of a house.

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There are three terminals on a 3-way switch. One is dark or black in color. This is called the common. The other two are brass or gold in color. These are called travelers. A normal single pole switch is either on or off. However, a 3-way switch switches the common terminal between one traveler terminal to the other traveler terminal.

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When working with electricity always:

Turn off the power.

Test the wires to ensure the power is off.

Lock out the panel box, so no one can accidentally turn the power back on while you are working.

NOTE: -Aluminum Wires- If you are using aluminum wires in this situation, it is very important that you use fixtures and/or wire connectors or wire nuts that are UL (Underwriters Laboratories) approved for use with aluminum and copper wires.

1) Wiring a 3-way light switch system

Wiring a 3-way switch is a simple step once you understand how a 3-way light switch system works. Notice the figure below.

Looking at the drawing you will notice that there are 3 sets of cables.1). One cable bringing in power.2). One cable going to the light(s).3). One cable connecting both 3-way switches.

The cable connecting both 3-way switches is a 3 wire cable. This means that there are actually 4 wires in the cable. Black, red, white, and a ground wire. The black and red wires are both connected to the traveler screws on the switches. It doesn't matter which one goes where. As you can see they're both the same.

Although there are many different ways a 3-way light switch system can be arranged, they're all wired the same. Example: The power cable may not come in the same switch box as the cable going to the light. One could go in one switch box and one in the other. However, it's still wired the same. The common on one switch always goes to power (black wire) and the common on the other switch always feeds the hot (or power) to the light. Also, the two traveler terminal wires always go to the other two terminal wires on the other switch.Top

2) Ground all switches.

Attach the ground wire (bare copper wire or green wire) to the ground screw of the switches. If more than one ground wire is in the box, twist them together along with a pigtail with a wire connector (wire nut) or a crimped connector. Next, attach the pigtail ground wire to the ground screw on the receptacle. If you are using a metal outlet box, make sure a pigtail ground wire is connected to the ground screw on the box.

NOTE: Before putting the cover plate on the switches, make sure the switch is aligned straight vertically before you tighten it down (to be visually pleasing). Also, do not over tighten the screws for the cover plate, as it may crack.

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