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Install & Replace

Three-Way Switch Doesn't Work Right

We have two three-way switches (we think) at either end of our hallway.  One of the switches is a dimmer switch.  The other is not.


The switch at the entrance to the hallway, the dimmable one, will turn on the light.  Then, we go to the end of the hall, and turn off the light.  If we go back to the entrance and flip the dimmable switch, it won't turn on the light again.  Moreover, if after doing that, we go back to the end of the hall and flip the other switch, it won't turn on the light again.


The only way we can control the light is to either turn it on or off from the entrance dimmable switch, or if we turn it off at the other end, then we have to turn it back on from that end.


What's going on?  How can we fix it?

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Posted 2012-10-25T20:36:24+0000  by thebigad thebigad

Hello thebidad.  Welcome to the Community!


It would help to know if you just installed these switches and things just don't work right, or if they used to work just fine and now they don't.  In the former case, you may simply have a miswiring issue.  In the latter, one of the switches has likely gone bad.


Three way switches work by alternating the power connection between 2 "legs" called travelers.  There are a pair of wires that run between the two switches.  Each switch powers one or the other leg at all times.  When both switches are aligned so that they both send power through the same leg, the light goes on.  See the diagram below.  The travelers I am talking about are shown as a pair of red wires that run between the two switches.


Dimmer Wiring.png


Many modern dimmers can be wired as both single switch or 3-way, hence the diagram you see above.  In addition, you can tell if a regular toggle switch is a 3-way by noticing that there is no "on or off" molded on to the toggle.  When in doubt,  pull the switch and look for that pair of travelers.  They do not have to be red, and often are not.  Ignoring the optional green ground, a 3-way will have 3 wires, and a single pole switch will only have 2.


One more idea; look at the 3-way dimmer diagram above.  If the power in line is hooked up to a traveler feed, you may also get the odd switching troubles you are experiencing.  


Is this what you are looking for?  Let me know if I can be of more assistance.





Posted 2012-10-26T20:22:04+0000  by Chris_HD_CHI

Thanks for the input.  We bought the house and the home inspector failed to notice the problem.  The diagram and your explanation is helpful.  Let me open up the plates and see what we have going on...

Posted 2012-10-29T13:43:32+0000  by thebigad

You're welcome thebigad.


If it turns out that this is a wiring problem instead of just a bad switch, a couple of things to note would be helpful.


First off, see if your wiring is inside conduit, or if cables, (NMB or often called Romex) are being used.  This will have an impact on both the wire colors being properly assigned as well as how easy it may be to fix.


Second has to do with wire colors.  There are "typical" colors used by convention that many electricians follow which can be helpful in figuring out what goes where.  Not everyone follows them, but sometimes this can help.


Let us know what you find.  We will try to help you as best we can.






Posted 2012-10-30T14:56:09+0000  by Chris_HD_CHI

I opened it up this weekend.  Here's what I found:


The entry dimmer three-way switch.  The black wire is hot.  The red wire appears to have been inserted in the "common" hole.


The other non-dimmer is also a three way switch.  But on this end, the white wire is hot.  And the black wire was in the "common" hole.  So, I thought this was simple, and put flipped the red/black wires, so that the red wire would be in the "common" hole, like in the dimmer three-way switch.  


When I did that, however, nothing worked at all.  So, I returned everything the way it was, and the lights work as before, but not properly as a three-way should.


What to do now?  Is there some kind of wiring issue?  Or should I try getting new switches?

Posted 2012-11-12T14:32:37+0000  by thebigad

Hello thebigad.


I think that you indeed have a wiring issue.

Look at the diagram below and see if this makes sense:

Three Way.png

You need 2 traveler wires for a 3 way switch to work properly.

In your description I only hear about 2 wires per switch as I tried to show in the diagram.

In this scenario, the light will turn on only when both switches are trying to power the same, (in this case the upper) traveler leg.  The "lower" traveler leg appears to be missing.


When working properly, the light would turn on when both switches power either the upper, or both switches power the lower traveler leg.  The light goes off when either switch changes power over to the traveler leg that the other switch is not powering.  In that way, either switch can complete the circuit and power the light when you flip its lever.


You also mention a white wire being used on a switch.  This is normally only done when the home is wired with cable, often called NM-B or "Romex" which is a trademark brand name.

In this case that white wire should be clearly marked with black electrical tape to indicate that it is a power wire instead of a neutral.  The problem is that it appears that you have a cable wired home, and not enough wires to correctly wire the 3-way switch setup.  The only way to run another wire would be to run new cable between the switches.  With tubular conduit this would be fairly easy, but with cable it usually is not.


I may be misinterpreting your posts, but if what I have said here makes sense you will have to rewire this circuit.

I recommend that you have an electrician look at this and get an estimate on what it will cost to remedy.






Posted 2012-11-13T15:08:56+0000  by Chris_HD_CHI
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