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I was working a side job today and re-wired quite a few 3 and 4-way circuits. I have a good understanding on how each work, but when I hooked up a 3-way dimmer on a 4-way circuit, the light would come on only if I had a certain switch on. Basically, I put it where I thought was at the switch leg end of the circuit. I'm only assuming this because the first 3-way is a foot away from the panel then the 4-way and finally the last 3-way. I've heard several people say to put it on the switch leg end (granted it's wired for a traditional 4-way circuit) or the switch that is not the line side. I also heard it does not matter... as long as it's obviously not in the middle. What the heck is the problem here???

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3 Answers

Was it a standard dimmer switch, rather than a 3-way one?

When replacing an on/off switch with a dimmer switch, you must make sure the type of switch (standard, 3-way, 4-way) matches. They make all three types of on/off switches, but I've only ever seen standard and 3-way dimmers. I figure the rarity of use for 4-way dimmers, combined with the rarity with which they would be purchased, make them not worth manufacturing.

Anyway, in a 4-way circuit (or more-way), you can replace either 3-way on/off switch (which will either be the first or last switch) with a 3-way dimmer. But it must be a 3-way dimmer, not a basic dimmer.

I refer you to some excellent diagrams on wikipedia to see how multi-way circuits work. Note the difference between how a 3-way and 4-way switch work. If you can find a 4-way dimmer switch, you could replace any 4-way switch in a multi-way circuit with it. Otherwise, it's either got to be the first or last switch.

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+1 But I have never seen or heard of a 4-way dimmer. 4-way switches are just reversers of connection (A1-A2, B1-B2 switches to A1-B2, B1-A2). You can have several 4-way switches in a circuit, so long as you have two 3-ways at either end. I think you can always substitute one 3-way dimmer for one of the 3-way regular switches. When wired right, every switch can turn on or off the lights, but usually only at the level the dimmer is set to. –  bib Oct 26 '12 at 13:29
    
Correct, no 4 way dimmers. The 3 way must be at either end of the switch legs, whatever it takes. If the dimmer is desired in a location where only a 4 way switch makes sense, the only solution is to extend the power and double back the switch legs so that it becomes the "end". If the OP's circuit is not working, either it's not a 3 way dimmer, the switch legs are run in a non-intuitive manner, or the dimmer is connected incorrectly (power to switch leg terminal). He seems to be knowledgeable, so the switch legs are probably run non-intuitively. –  bcworkz Oct 26 '12 at 20:18
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Let's get our lingo straight. In a 4-way switch network, there are 3 switches:

1) Line end 3-way switch

2) middle of network 4-way switch

3) load end 3-way switch

If you want to install a dimmer, I'd buy a Lutron 3-way dimmer at a compatible wattage for the load. Identify which of the 3 switches is at the Line end. The common lug on this Line End switch remains hot (120 VAC) when you toggle its switch. This Line End 3-way is the one you replace with the 3-way dimmer.

Sounds like you tried to install the dimmer at the Load End. As you describe, the switch on the dimmer was not sufficient to toggle the load state. That's because the Line voltage coming to it is conditional on the first two switch settings.

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Here is how three way and four way switches should be wired: enter image description here

For deeper understanding, here is what it looks like schematically: enter image description here

And here are specifics about wire marking and the different types of romex used: enter image description here

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