3-way light switch hookup

Old 01-26-03, 04:19 PM
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3-way light switch hookup


I have two sets of wires coming out of the wall for a stairway light that can be turned on and off from two different switches (one upstairs and one downstairs).

Each set of wires has a ground, a black, and a white wire. My new light fixture has one white, one black, and one ground wire. I forgot to mark the wires before disconnected the old light. Can someone give me some guidance on how to hook up these wires?


Old 01-26-03, 06:18 PM
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Chances are you have a switch loop. If you described the wiring at the switches, it would be more clear, but we can probably work without that information.

First, you need to identify which of the two sets of wires is the power cable, and which is the switch cable. If you have a voltmeter or circuit tester, you can use that to determine. Otherwise, you can use the light fixture itself.

Here's what to do, assuming you're going to use the light fixture as your tester:[list=1][*]Turn off the breaker.[*]Connect the light fixture to just one of the two sets of wires. Pick either set at random. Make sure the other set of wires are separated and not touching anything.[*]Turn the breaker back on.[*]If the light is on and unaffected by either switch, then the cable you connected to is the power cable ("P"). But if the light is off and unaffected by either switch, then the cable you connected to is the switch cable ("S"). If the light is affected by a switch, then you don't have a switch loop and will need to stop now and post back for more instructions.[*]If you'd like an extra measure of security, turn the breaker off, connect the fixture to the other set of wires, turn the breaker back on again and repeat the prior step.[*]Turn the breaker back off again.[*]Connect Pb (power cable black wire) to Sw (switch cable white wire).[*]Connect Pw to the white from the light fixture.[*]Connect Sb to the black from the light fixture.[/list=1]Of course, connect all grounding wires. And mark the end of Sw with a black marker (if one of the white wires is already marked black, then you can skip the testing because you know that that cable is "S").
Old 01-26-03, 11:04 PM
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3-way switch


much thanks! it works, and i didn't fry!


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