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3 way wiring question

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  • 3 way wiring question

    A friend of mine just moved into a house and tried to change his dining room overhead light, which is controlled by two switches. The way he installed it keeps tripping the breaker b/c he didn't understand that there's a different way to wire 3-way setups. Perhaps someone here with more electrical experience can tell me the correct wiring so that I can pass it on.

    He has two separate wires entering the ceiling box. Leaving out the ground wires, one wire has white and black. The other wire has white, black, and red. The fixture obviously has white and black.


  • #2
    Something appears to be missing. Each switch should have 3 wires leaving it. One wire is a power wire and the other two are "travellers", allowing for the toggling of current between the switches. In your description, it sounds like the connections are made in the ceiling box. There should be a total of 10 wires and 5 connections in the ceiling box, assuming the light is wired between the two switches. You mentioned only 7 wires. Are there more wires?
    there's a solution to every just have to be willing to find it.


    • #3
      I agree, if you have one 14/3 to the light you must have another 14/3. My bet is that he assumed that the white wire from one of the travelers was neutral and tied it to the real neutral which will pop the breaker because the white traveler is really hot. That white wire should have had black electrical tape wrapped on it to indicate that it was hot.
      With the power off untie all the wire nuts and pull the wires apart. Use a meter and check both white wires to the bare wire, the one that show 0 ohms is the true neutral and that ties to the white from the light. The other white is a traveler, to prove this to yourself you will have 0 ohms between white and one of the black or red wires from the same 14/3 wire. To determine which wire is common pull both 3-ways out or the wall, one of them will only have 1 14/3 in the box the other will have 14/3 and 14/2 (power feed). On the switch that only has the 14/3 look at what colour wire is on the black (common) screw on the 3-way switch. At the light box the 14/3 that did not have the common wire in it has the wire from the switch that you just looked at. Test to be sure, attach the colour that was on the common to one wire of the meter you will have 0 ohm between one of the other two wires, flip the switch and it should now be open and the remaining wire will be 0 ohms, flip the switch and that wire will now be open. Take that colour of wire that was on the black screw and tie it to the black wire from the light. The 4 left over wires (2 from each 14/3) are the travelers and tie together red to red and black to black or white (depends what colour was on common). Put black tape on the white traveler to indicate that it is hot


      • #4
        Robert Wilber
        Licensed Philadelphia Electrician
        Philadelphia License # 3516 - 16765
        (LIFE SAFETY WARNING! [disclaimer]
        Electricity is dangerous!
        You can be injured or killed!
        Improper installations can cause fire, injury and death!
        Should you be doing this yourself?)
        I think you are all asleep at the switch
        It sounds like there is NO 3 way operation [probably]
        what we have here is a failure to communicate ....
        There are two cables at the light/fan box and 2 switches controlling it.
        I didn't hear anyone say there was a three way operation
        there are 2 switches. period.
        I suspect that the box was wired so you could have a fan and light controlled by two switches at the same location. Am I right?
        I think that the feed comes in on the 2-wire. period. The 3-wire is a dual switch leg, and there are 2 single pole switches. period.
        If this is the case ---'cause the guy didn't say he changed anything at the switches....
        the black from the 2-wire is the hot feed.
        The White from the 2-wire is the neutral.
        The white from the three wire goes to the black from the 2-wire and is wirenutted and pushed in the box. alone, to carry the hot to the switches [switch leg]
        The white from the 2-wire goes to the wire from the fan/light combo.
        The red is the return from one of the 2 switches. this gets connected tro the black or the blue [light] of the fan/light.
        The black is the OTHER switched hot, which gets connected to the light/fan wire [black or blue] that you didn't connect to the red.
        I believe this will make the problem go away ... [if I understand the problem correctly]
        Licensed Philadelphia electrician
        Philadelphia emergency lighting certification


        • #5
          Yeah, RobertWilbur, I think you're theory is right on. I haven't seen the setup; I'm just going by what was told to me.

          The replacement fixture is not a combo, just a light. I think that is causing some confusion because the wire that would get connected to the blue wire is now left without a mate. What happens in this case?


          • #6
            In that case, one of the wires [either the black or red] would not be connected to anything.
            ... and just cap off the blue wire.
            Perhaps the best case would be to contact your friend and get more information, or perhaps have him read this thread and comment.
            It would be easier to reach a useful conclusion if we had the details to examine.
            I have played "whisper down the lane" before ...
            Licensed Philadelphia electrician
            Philadelphia emergency lighting certification


            • #7
              Re: 3 way wiring question