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I have a three-way switch where I would see a spark behind the switch every time I tapped it, so I wanted to replace the switch. Upon replacing the switch and wiring it all up as before, I now get a short (circuit breaker trips) whenever the switch is in the "on" position. If I take the switch out and connect the "hot" wire to one of the two travelers (or leave the 3-way in question off), the other 3-way switch in the circuit, and the light that they control works fine, but if I connect the "hot" to the other traveler, the breaker trips instantly.

Here's a diagram of the wiring in the box. I've only investigated this box; not the one housing the other 3-way switch, so that's not included. S1 is the switch in question; I don't believe S2 is related, but it's also in the box and shares some wires so I've included it. Circles represent where wires are coming into the box; squares are switches; and triangles are pigtails. Finally, both switches are grounded through the box; there are no ground wires in this diagram. Forgive my bad diagram, and if I've misused any words here; I'm new at this stuff!

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Questions:

  • Does this wiring make sense?
  • How can I find the source of the short? I've inspected all the wires and everything appears to be sheathed correctly and not contacting any other wires or the box.
  • I haven't opened the other switch which shares control over the light. Is it possible the problem lies there?
  • Any other ideas, or anything else I should check?
  • Can you post photos of the insides of the boxes? – ThreePhaseEel May 6 '17 at 21:56
  • The usual problem with 3-ways is putting the wires on the new switch in the exact same physical position as on the old switch, and not paying any attention whatsoever to the colors of the screws, which determine which wire is common and which are travelers. Those positions are not consistent on different models of switch. – Harper - Reinstate Monica May 7 '17 at 3:00
  • @nvioli Looks like you have only one 3 Way and one normal switch - you are supposed to have two 3 way switches – Ken May 7 '17 at 4:31
  • @Ken he said in the text he excluded the other 3-way from the drawing. This being the problem. He is confused as to which wires are messengers, because he focused on the physicality of the wiring rather than the functionality. – Harper - Reinstate Monica Jun 11 '17 at 15:20
  • @Harper - after rereading, yes you are correct he states it is not part of the drawing (which he should have as it is part of the circuit)- which would have allowed him to resolve his problem more easily. I did post the wiring of a 3 way for the op - so he could verify what he had with what was in the drawing. As it turns out he had his traveler and hot mixed up. – Ken Jun 12 '17 at 20:42
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I apparently wasn't paying attention when I took the old switch out, and had reversed the positions of the power wire with one of the travelers. I was sure that the power wire attached to the black screw on the switch, but when someone else looked at the switch, he suggested the power wire should go to one of the brass screws. After wiring everything back up the switch is now working.

  • Indeed, that is the #1 mistake people make with 3-ways. They look at the physical positions of the wires, and move the wires over to the new switch in the corresponding physical positions. Unfortunately, manufacturers like to put the common in a different place on every switch. – Harper - Reinstate Monica Jun 12 '17 at 20:53
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You should have a 3 Way switch as S1 and a 3 way switch as S2 and a traveler.

See the diagram below.

3 Way Switch Diagram

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