Go to How Not to Build an Addition Index! This page includes notes on three way switches.


A three-way switch sounds like a scam where the police, the CIA and the Mafia end up trading briefcases at the end of a spy thriller. The hero and his girl, by some slick maneuver, walk off with a cool million dollars.

Unfortunately, three-way switches have nothing to do with briefcases filled with money. Instead, the three-way switch is about the most complicated wiring you will be called upon to do in your new addition. It is complicated because a three-way switch is really only two switches, at least in the way that you and I understand them. They are used to control the electrical flow at one point from two different locations. For example, a light in a stairwell might have a switch at both the top and the base of the stairs. So why do they call it a three-way switch? It is to confuse the layman, of course.

To properly do this job, it is best to get a special kind of wire. I call it three-way switch wire. Along with the usual black, white and ground strand, you get a red strand. You also need TWO special switches. The switch boxes and the light junction box are easy enough to place. The key to the situation is knowing which wire to hook to which part of each switch. In the entrance to my house from the garage I installed a three-way switch. I solved the wire-to-switch problem by asking myself: where is the power coming from? and where it will terminate? I placed my hands together and bowed my head so that my forehead touched my fingertips (a little prayer never hurts). Then I hooked up the wires. My first test proved uneventful - no light. On my second wire arrangement, only one switch combination turned on the light. The third attempt was quite spectacular: smoke, fire and brimstone burst forth from both switches. Luckily the fuse box was in the same room. I broke the circuit in a hurry.

Undaunted by this setback, I went to the hardware store and got new switches. I rightly figured that there were only so many possible wire and switch combinations. Four switches and an expended fire extinguisher later, I had the three-way switch in proper working order.


People have been killed while working with electricity when they did not know what they were doing. Then again, people have been killed from blowing their nose too hard, and they did know what they were doing. So be careful, use your common sense, and in this one case, maybe look at a book on electricity before beginning.

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Fuse Box
Three Way Switch

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About the Author:
W.J. Rayment built an addition on his house, and in the course of the project learned from his many mistakes. This on-line compendium is his effort to help you learn from his experience. The advice and stories are often humorous, sometimes silly, but always informative. for yourself or as a gift for family or friends.

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