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I have a 3 way switch that was wired incorrectly when the switches were replaced with a different color switch. Is there a methodical way for me to identify which wires represent which piece of the system so I can correct the bad wiring?

Currently if switch 1 is on, switch 2 can turn light on or off. If switch 1 is off, then switch 2 does nothing.

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3 Answers

up vote 17 down vote accepted

I had this EXACT issue when I moved into my new (to me) house. The original owner was a bit of a handyman and had done several small (and big) projects all over. In many cases regarding electrical work he'd done, I had to go back in and clean up.

Here's a fail-safe process to fix a three way setup that isn't working:

  1. Turn off the breaker controlling this light. You may also need to cut additional breakers if either or both of the 3-ways are in "multi-gang" boxes with other switches on different circuits. Use a non-contact voltage tester to ensure all of the screws on the side of all the switches in both boxes are dead before pulling out any switches.
  2. Disconnect all wires from both of the 3-way switches (but do not unwrap or un-nut any of the twisted wire bundles, or disassemble any other switches). Pull these wires out of the box and separate them so there is no bare copper touching any other metal.
  3. Turn the panel breaker back on. From this moment until step 5, the second you are not extremely cautious around every bit of bare metal in that box, you will pay for it.
  4. Probe all the wires you disconnected and separated one at a time with your non-contact voltage tester, being extremely careful not to touch any of the other wires with the tester or any part of you. You will find one loose black wire in one of the two boxes that is live, and all other wires should be dead. The live wire is your panel hot; remember it.
  5. Turn off the breaker at the panel again.
  6. Back at the box with the wire you identified as the panel hot, connect the hot wire to the "common" terminal of the 3-way switch for that box. Looking at the body of a three-way switch, the common terminal is the terminal that has another terminal screw on the switch body facing the same way, but doesn't have a screw directly across the switch body facing the other way. A picture's worth a thousand words; see below.
  7. The other two insulated wires you removed from the switch are the "traveler" wires. One will be black, and the other red, and they should both be a part of the same "trunk" of Romex wire. Connect the black to one of the remaining terminals other than the grounding terminal, and the red to the other terminal.
  8. Both of the two wire "trunks" should have white and bare wires in addition to the black and/or red; ALL the white wires in the box should be twisted into a bundle with a wire nut, and all bares should be twisted in a bundle with or without a nut.
  9. Screw the terminals down firmly, attach the ground wire to the green grounding terminal screw if one was connected (bathrooms require a bare wire ground to be connected to the switch, most other rooms don't), cover all the switch terminals with a layer or two of electrical tape, and, being careful not to short out any wires, push the wires and switch back into the J-box and screw it down.

A three-way switch, with terminals identified

  1. Now, go to the other switch box. Examine the loose wires which you disconnected from the switch (there should be two black and one red). The black wire that doesn't go into the same outer insulation conduit as the red wire is the hot lead to the light. The other two wires are the other ends of your traveler line. Both these "trunks" should have white and bare wires in addition to the black and/or red; the white wires should be twisted into a bundle with a wire nut, and bares should be twisted in a bundle with or without a nut.
  2. Connect the light's hot wire to the switch's common terminal.
  3. One note; if you connect the black wire from the traveler to the same side of the second switch that you connected the black traveler wire to on the first switch, the switches must be set opposite each other (one up and one down) for the light to be off. Personally, I prefer to be able to turn every light in the house off by pushing all the light switches down. If you're like me, then swap the red and black wires of the traveler pair, connecting the black wire to the opposite traveler terminal from the one you used on the first switch. This will result in the circuit being off when the switches are set the same way (both down or up).
  4. Connect the traveler wires to the other switch terminals in the manner you choose, and connect the ground if you have one. Wrap the terminals in electrical tape, and put the switch back in the wall box.
  5. Turn the panel breaker(s) back on. Have another person stand at one switch, while you stand at the other. If the light is on, flip one of the switches. Now, have the other person flip their switch; the light goes on. Flip yours (light off). Flip theirs again (light on), then flip yours again (light off). You've now gone through all four combinations of light positions, and verified that either switch can turn the light on or off.
  6. If something still doesn't work, turn off the panel and take the switches out of the box (but don't disconnect them). Make sure none of the terminals are shorting out against any other piece of metal in the box (including the box itself, if it's conductive). If it STILL doesn't work, replace one or both switches (they're about $3 a pop). if it STILL doesn't work, I'd call an electrician; there may be a break in the wires of this circuit, or there may have been a mix-up involving multiple switches in the boxes; pretty much any way you slice it it could be dangerous or expensive for you to continue to try to fix it.
  7. Once the switches are working to your satisfaction, put the switch plate back on over the box (make sure before you start screwing in plate screws that ALL the holes line up), and enjoy your repaired three-way circuit.
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+1 awesome details –  shufler Dec 12 '11 at 20:01
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Can we get instructions that don't assume you can see which wires come from which outer insulation conduits in Part II step 1? And that don't assume the color of the wires? –  emmby Apr 26 '12 at 3:28
    
If you're not sure about the wires in the second box, disconnect all the wires from the second switch (with the first wired up) and then turn the power back on. Have someone else stand at the other switch, and when you tell them, toggle it. Probe the wires with your NCVT and you will find two wires that alternate getting power. These are your "travelers" ("black" and "red" wires). Turn the power back off, then try pulling on those wires; if they're Romex, one more jacketed wire and a bare wire wire will move with them. The jacketed wire is neutral and the bare is ground. –  KeithS Apr 26 '12 at 14:38
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As far as the colors, the NEC mandates that white-jacketed wires must be neutrals, and green or bare wires must be grounds. All other wires in one bundle are "hot"; the current convention is black and red, but brown, orange and yellow have been used in the past and are still used in 3-phase wire. In any case, you should be able to tell which colors of wire you're looking for from your 4-conductor bundle after wiring the first switch. If you can't tell, you either have really old non-Romex, or some paint crew was a little overzealous; try scraping a little paint off to uncover the insulation. –  KeithS Apr 26 '12 at 14:49
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Just for reference: NEC 200.6 Means of Identifying Grounded Conductors., covers neutral markings. While NEC 250.119 Identification of Equipment Grounding Conductors. handles Ground markings. –  Tester101 Sep 19 '12 at 12:30
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As Karl points out, first find the hot (source) wire. On a standard three way switch, this is usually attached to the screw on the side of the switch that only has one screw. The screw on the switch is usually a darker color too. There will be one of these on each switch obviously, so there are really only two wires to test. Use a multimeter by touching the wire, and the other lead from the multimeter to the white (in the US) or to ground.

Once you find the hot, the wire attached to the other switch on the side with the single screw is probably the one that goes to your lights.

The other two wires should be attached to both switches, and these are called the travelers. They let the power move from one switch to the other switch, and alternate sending power based which way the switch is positions. So one of these is always hot.

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Since testing for the hot (line) and load conductors requires having the power turned on, use extreme caution. Wear gloves and disconnect the power as soon as the test is complete before changing your wiring around. Also be sure to operate the switch with the meter in place to be sure you have the line wire properly identified. The 120vac will be present no matter how the switches are positioned from either side. The load wire will turn on and off as you toggle either switch. –  shirlock homes Aug 12 '11 at 10:27
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Yes. You will need some basic testing equipment; a multimeter should do. There will be a live wire coming in one box, and two traveller wires also in that box (usually a black/white pair.) The traveler pair will go to the other box.

Use your multimeter to figure out what is live whe nothing else is. This is the hot 'in' wire. The next two wires are the traveler. The third wire in the other box at the far end of the traveler is the wire that goes to the Fixture. It sounds like the traveler on the far side of the box might have gotten swapped with one of the wires to the fixture. Just take it apart, figure out which wire is supposed to be which, and put it back together right.

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the travelers are also frequently the red and black wires. –  mohlsen Aug 11 '11 at 11:45
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