How to Replace a 3 Way Switch and the dangers of not calling an Electrical Professional

As a Licensed Electrical Contractor I find the most common calls I receive from “Do-It-Yourselfer’s” is about changing a switch or receptacle. I hope by reading this article I can shed some light on your task at hand. Since it can be quite confusing even for some electricians, I am going to some detail on the 3 way switch topic. Please read through the complete article to get a good grasp of the how a 3 way switch is wired.

Here are a couple scenarios of the main calls I get from my customers….

“I replaced my 3 way switches and now the bedroom lights turn off when I flip the switch”. There are a few reasons for this. But the most common reason is.

When the homeowner disconnected the switch they took splices apart in the box and when they reconnected them they were not in the proper configuration. This can be quite dangerous and expensive. In one case the homeowner had his brand new plasma TV and Stereo system totally… “Fried” When he reconnected his splices he hooked up 220 volts to that outlet.

“I replaced my 3 way switches for my hall. Now when I turn the light off at one end of the hall, I can’t turn it back on from the other”.

This is usually a simple fix. There is a pair of wires called “travelers” and in this situation they are usually reversed with the common wire.
I also receive numerous calls about this from general contractors, handymen, maintenance personal, etc…

Now before we go any further with this article. I want you to understand that I am not writing this article to teach you how to repair or replace a 3 way switch or 3 way systems. I am writing to try and make the point that this is one of those situations where you can end up in some real hot water, and you should call a service professional if you do not have the proper electrical knowledge.

There are many ways to wire a 3 way system. I am going to show you 3 configurations of a 3 way system.
Do not confuse this with a 4 way system!!! (A system with 3 or more switches)

The First thing you need to know. A 3 way system only has 2 switches. If you have any more or less you are not looking at a 3 way system.

Figure 1 (Example 3 way switch)