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I'm having trouble with a three-way switch. (It may be 4-way, there are switches in my house I can't figure out). I don't recall if they ever worked properly. The light stays on regardless of the switch position. I've disconnected both switches and tested the wires. Here's what I've got:

Downstairs: 2 black (one hot), one red (hot) Upstairs: 1 black, 1 white (hot), one red (hot), 1 ground

I thought there was only supposed to be 1 hot wire in each box?

  • My wife now assures me that this outdoor light did work properly at one point. So now I'm thinking maybe I'm testing the wires wrong? I used a voltage probe and it beeped at the wires noted above. Is there another way I should test to find the hot wires? – StepByStep Jan 19 '15 at 18:41
  • My answer just below outlines which wires should be hot or not. If the switches are still wired up and the breaker is on, one of the travelers is always going to be hot in both boxes. – Craig Jan 19 '15 at 19:48
  • I removed the switches before testing the wires. That's why I'm concerned that there are 2 hot wires at each switch when the breaker is on. It looks like there should only be 1 hot wire per switch. To me that means I'm doing something wrong or something needs to be fixed. – StepByStep Jan 19 '15 at 20:36
  • If the switches are disconnected from the wires, and there are only 3 conductors in each box, then there should only be 1 hot wire in 1 of the boxes, and no hot wires in the other. The switches operate by transferring juice from the hot in that one box, over one of the travelers, then out the common on the other switch to your load (light fixture). It might be time to call an electrician. ;-) – Craig Jan 19 '15 at 20:43
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    It might be time to call an electrician. Yep. I think I'm going to do that. – StepByStep Jan 20 '15 at 0:59
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It sounds like you have power entering the junction box at the light fixture, then running to one of the switches. If you actually have power entering both switch boxes independently, this will never work and you need to look at the connections at the light fixture.

EDIT Here's a 3-way switch:

enter image description here

Here's what should be happening in your case in order for the switches to work:

  • One wire, entering one switch box, should be hot from the power source (if the circuit breaker is on, this wire is hot).

  • That hot wire should be connected to the common screw on the 3-way switch.

  • The travelers (the other two screws on the switch) should run straight from one switch to the other, with no other connections along the way, through the light fixture's j-box. (the travelers from each side will be connected to each other with wire nuts in the j-box, of course).

  • The wire that is attached to the common terminal on the other 3-way switch should be connected to the black wire on the light fixture. This is the power coming out of the switches.

  • The white wire on the light fixture should be connected (wire nut) directly to the neutral wire in the j-box under the light fixture. If you're using Romex, this is going to be the white wire in the 14-2 or 12-2 cable that supplies power into that j-box.

Here's another StackExchange answer that shows very simply how 3-way switches function.

And another very long, detailed answer (holy smoke, I thought my answer was too long).

This diagram shows 3-way switches with power entering the light fixture box, and seems less confusing than many. It's surprising how many mislabeled diagrams of 3-way switches there are out there:

enter image description here http://cindyjerrell.com/artwork/2012554_3_Way_Switch_Wiring_Diagram.html

A little more explanation

There are different ways to physically wire up 3 way switches, depending on whether power enters one of the switch boxes or enters the switched fixture. But they all add up to exactly the same thing.

You have 3 terminals on each switch. The different-colored one (usually darker) is the common, and the other two are "travelers."

So you have 2 travelers. This is usually the red and white, if your wiring is NM/Romex 3-rope, and you would use a black permanent marker or wrap black tape around the end of the white wire to indicate it is a hot conductor (not a neutral) in the switch circuit.

It sounds like you have something other than NM 3-rope going on in the wall between the light fixture and one of the switches (not the end of the world--electricity doesn't care about the color of the insulation on the wire).

The travelers always run straight between the same-colored terminals on both 3-way switches, no other connections

Depending on the positions of the switches, one of the travelers is always hot.

If the switches are positioned so that the common on both ends is connected to the hot traveler (which could be either traveler), then the circuit is complete and the light comes on.

The purpose of the travelers is to complete or break an electrical connection between the common terminals on the 3-way switches.

Now that the travelers are out of the way (connect them to the two same-colored terminals on the switches, forget about them), consider the common terminals...

Regardless of where the power enters the circuit, you run your hot wire to the common terminal on one switch, and wire the hot lead on your fixture to the common terminal on the other switch.

The entire set of 3-way switches, as a whole, just switches the juice on the common terminal of the 3-way switch at the opposite end.

  • A particular critique would be that second diagram shows white wires used without any tape with a color other than green to mark it as a ungrounded conductor. – ChiefTwoPencils Jan 19 '15 at 10:01
  • @ChiefTwoPencils I did talk about that in the 3rd paragraph after "A little more explanation," just beneath the diagram. ;-) – Craig Jan 19 '15 at 18:19
  • Yeah, my concern was if someone neglected to read it all or just shoot straight to the pic and go to work. IMHO, your answer is nice and detailed, but the diagram is a bit misleading. IIWM I'd make a point to not use white; that's all. – ChiefTwoPencils Jan 19 '15 at 20:30
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After hunting around the web incessantly for an answer I could truly grok, I found stackexchange and digested the "usual" 3-way switch solution thusly (as Sheldon Cooper would say):

  1. Begin by removing both switches.
  2. After getting taught a lesson about respect for electricity, turn off the circuit breaker and then continue removing both switches.
  3. Between both swithces, one wire (and one wire only) should be hot. Label it as your "panel hot."
  4. Install one switch at that location; wiring the "panel hot" line to that switch's Common/Hot screw. Then wire the other two wires on that switch.
  5. Go to the other switch. Toggling the first switch and testing the wires for the second switch will reveal one wire on the second switch which is never hot no matter the position of the first switch. This goes to the light. Wire it to the second switch's Common/Hot screw. Then wire the other two wires (which are the travelers) on the second switch.
  6. Test both switches; they should work unless there's something messed up at the light.
  7. Like many others, I prefer the light to be OFF when both switches are in the down position, ESPECIALLY for a light that's hard to reach. If you didn't chose wisely the first time, just reverse the travelers on one of the switches.

Thanks to all.

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