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3-way switch - identifying the common wire.

Posted by Andrew Dodd on October 5th, 1999 09:51 PM

0 of 4 people found this post helpful

How does one identify the common wire on a 3-way switch?

Here's the problem: I have three wires, one red, one white, one black.

From what I've seen, common wiring practice means that the black wire is common, but in my apartment, this doesn't seem to be the case.

The other possibility is that the common terminal on my 3-way switch is not the one I think it is. They're all the same color. :(

As to how I got into this mess: I use X-10 home automation products, and have installed lamp modules and wall switches in numerous locations. I needed a 3-way switch for the stairwell here, so I ordered one. It came in today, and I decided to wire it. I followed the instructions for the switch, turned the breaker on, and pushed the button. No light. After trying all three of the wires I had as a common, the switch still didn't work. So I reinstalled the old switch. Unfortunately, now it only turns on when both switches are in the down position. From the looks of it, I've accidentally wired the common to one of the travelers. The problem is how to identify which wire/terminal is which now.

I'm assuming I'll probably need to either find my voltmeter or borrow a friend's.

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