3 wire wiring question

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  #1  
Old 12-19-13, 07:27 PM
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3 wire wiring question

I am changing out a light fixture in my basement. I pulled the light off before realizing that the wiring situation in the box was a little more complicated. The fixture was switched, in that it could be turned on/off from 2 different light switches in the house. I have included a diagram of how it is currently wired up. In the diagram, the grey wires are really white, as I couldn't use white wire on a white background in the picture.

What I need to know is: which connections do I hook up the white and black wires to from my new light fixture? Obviously the ground goes the 3 ground wires and neither the black or white from the new fixture goes with the red.

Does the white wire from the new fixture go to the black(3)/white(1), black(2)/black(1) or the white(3)/white(2)? Then the same question for the black wire from the new fixture.

Thanks for any help.

 
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Old 12-19-13, 08:14 PM
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Did you make any changes other than removing the old fixture? Which cable has the power into the box? It looks like cable 3.
 
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Old 12-19-13, 08:20 PM
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No I didn't make any changes to the wiring, other than removing the old fixture (which had 3 wires, ground/black/white) I wasn't expecting the more complicated wiring job, otherwise I would have taken note of where each wire was attached before removing the fixture.

I don't know which cable has the power into the box. Do you mean which cable runs back to the panel?
 
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Old 12-19-13, 08:31 PM
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It looks like cable 3 is feeding a switch loop in cable 1. If so the red looks like a constant hot while the black in cable 1 is the switched hot. Try connecting fixture black to the blacks from cable 1 and 2 and the whites to the whites from cable 2 and 3.
 
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Old 12-19-13, 08:34 PM
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That's an interesting question. I've been trying to figure out how to answer it without testing, and I haven't had any luck. So here goes with the simplest test:

Kill the power. Tag the white wire that's spliced to the black wire with a bit of electrical tape. Tag the black wire it's spliced to the same way.

Take that splice and the other three non-ground splices apart and separate the wires. Turn the power on and use a multimeter - preferably an analog one - to test for 120V between each black wire and each white wire. Do the same for each red wire. Then test from each black wire and each red wire to ground.

Flip one switch and repeat the tests. Post back with the results and we may be able to solve it without having to open the two switch boxes.
 
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Old 12-19-13, 08:36 PM
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It looks like cable 3 is feeding a switch loop in cable 1. If so the red looks like a constant hot while the black in cable 1 is the switched hot. Try connecting fixture black to the blacks from cable 1 and 2 and the whites to the whites from cable 2 and 3.
That's my first off-the-cuff guess too. It's the connection of the black wires between cables 1 and 2 that made me hesitate.
 
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Old 12-19-13, 08:42 PM
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The red looks like a constant hot in cable 3, but there is no neutral.
 
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Old 12-19-13, 09:02 PM
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The red looks like a constant hot in cable 3, but there is no neutral.
Or a traveler.............................
 
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Old 12-19-13, 09:18 PM
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I don't have a multimeter to test. My father in law, who knows quite a bit about wiring, also suggested the black to black/black and white to white/white.
 
  #10  
Old 12-19-13, 09:23 PM
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If it helps clarify things, there are 2 lights that are switched. This light that I have removed, and another light about 6 feet away are both controlled by the same switch. The other light fixture I have already replaced, and it had the "standard" black/white/ground runs, and did not have a red wire at all.
 
  #11  
Old 12-19-13, 10:10 PM
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So I hooked up the new fixtures white to the white/white, and the new fixtures black to the black/black and everything is working. Can I assume that since the light works and I didn't blow a circuit that the wiring is correct and I won't be doing any harm?
 
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Old 12-19-13, 11:14 PM
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As long as the ground wires are connected..... then you can assume you've wired it correctly or you would have some immediate negative results.





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