How to Properly Wire a 3-Way Switch
One of the most frustrating things to do is to troubleshoot a 3-way switch that is not working properly. Sometimes the light switch is replaced and the wires were not coded properly to let subsequent people make future replacements easily. This occurred most often in the past when electricians used standard 12/2 wire for running the travelling wire between the 3-way switch and the fixture. Other times a standard switch was installed instead and the 3-way function was lost; this is the annoying problem when you lift one switch at it works fine until someone changes the position of the other switch. This article will give instructions on properly wiring a 3-way switch.
12/2 and 12/3 Cables
The most common switches are 2, 3 and 4-way; most people have at least one 3-way switch in their home, either at the top and bottom of your stairway or the light fixture in your family or dinning room. Receptacles can also be on a 3-way switch to control lamps. A 4-way switch is used to control a fixture from three or more locations.
You can tell what type of switch you have by the number of screws on the sides. The number of screws indicates the switch type, excluding the green grounding screw.
The basic diagram for a 3-way switch can be found below. Notice that the white wire totally bypasses the switches and goes directly to the light. Older homes can get tricky as the installing electrician could have run 2 sets of 2-wire between the switches, leaving you with a black and white system that is anything but black and white.
Hot = Black
Neutral = White
Traveler = Red and Black between switches
Common Screw = usually brass screw terminal on the side with 2 screws and diagonal from the single screw.
1. Bring the power supply in to one of the switch boxes (one hot, and one neutral), on a 14/2-wire cable. (Can be 12 or 14 gauge wire, check with your local code official)
2. Run a 14/3-wire to the other switch location.
3. From the second switch, run another 14/2-wire up to the light box. Notice that you should only have two wires coming into the powered switch and in the light fixture box.
4. In the first box, splice the neutral wire from the power supply to the white wire in the 3-wire cable going to the other switch.
5. Attach the hot wire to the common screw on the 3-way switch. (WARNING: This is where most problems occur when rewiring switches!)
6. The red and the black conductor from the 14/3 cable will be called the “travelers”, and will hook up to the two remaining screws on the switch.
7. At second switch, connect the white wire from the 14/3 to the white wire going up to the light.
8. The “travelers” (black and red) from the 14/3 will connect to the same screws as on the other 3-way switch, and the black wire going to the light will tie on to the common screw. (See # 5)
Sometimes electricians will run the red wire to the common screw and code a white wire with black electrical tape. I don’t know why, but it depends on who you learned from as to how you wire a switch. If you are replacing a bad switch, or installing a 3-way dimmer, mark you wires and hook them up the same way. As long as you know what wires are travelers and which one is connected to the common screw, you should be fine.