multiway-switch
I have two 3 way switches controlling one light. Sometimes when the light is on neither switch will turn off the light but one of the switches will turn light off if switch is placed half way between on and off. Would this be the switch that is wired wrong or do I have to take off the plates and look at wiring of both ?
In both pics the left most switch are the problem ones. Strange thing is they both looked wired correct. It appears the travelers red and black are both on bottom.
I agree with gregmac that is probably a wiring problem. If it isn't a wiring problem it's probably the dimmer and the dimmer itself may even be the wrong type. You might think about getting another three way switch and replacing the dimmer for test purposes only. If it works with the 3 way switch you know it's the dimmer. If it doesn't work then I would bet the dimmer was miss-wired when it was installed and I would start to see if the carriers and the line/load conductors are on the right terminals of the switch. If that isn't the problem then you probably need on site help to troubleshoot the problem.
I am assuming that most of us don't want to answer this question is because it takes quite a bit of work to try and explain how to troubleshoot the circuitry. Not that it's hard but as my instructors told me "it's easy once you learn how to do it."
Hope this helps.
I think your wiring situation looks like this
I believe it is a 3-way circuit, and the lack of any red wires, indicates the person used a cheat: using two 14/2 cables paired when he should have used 14/3 (with the red wire). So this accounts for two cables in both boxes. This leaves only one cable in the "smart switch" box. With only one cable remaining, that can only go to the lamp, meaning power is coming into the lamp, not the switch. The entire 3-way complex is a switch loop.
Since all your wires are black and white, I took the liberty of adding tape to color-code the actual functions. Where a wire is taped, think like the tape color is now the wire color. Now in any of these cables, it may be used the other way around, e.g. white for switched hot. In the 2-cable segment, any wire can be any of the functions. I am guessing.
I use yellow for both messengers because they both do the same thing, are both interchangeable (you can swap them and it won't do any harm). However they are not the same, landing both messengers on one screw terminal will not work.
Note that in the first (right) switch box, there is always-hot and switched-hot.
There is no neutral in a switch loop. Ergo you will not have much luck making that smart-switch work.
Best Answer
Get an electrician with an insulation resistance tester in to check this out further
Since both 3 way switches appear to be wired correctly, the one cause left remaining in the wiring system is a short between the two traveler wires themselves. To find this, I would have an electrician come in and unhook both traveler wires at both ends, then measure between them with an insulation resistance tester (often called a "megger"). From there, it would be a matter of chasing down any shorts found, and replacing either the entire cable or patching in a section of cable using NM splice kits to repair the situation.
If it isn't that, then I'd have the switches themselves checked, although that's less likely than an errant staple or nail causing a short.