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I just bought a 3-way dimmer switch for the kitchen. There are only two switches that switch the overhead lights. I went to take off one of them to install the dimmer and the switch had 5 wires (2 red, 2 black and a ground) hooked up to it. That would imply to me that it's a 4-way switch, but there's only two switches. What gives?

EDIT

I solved the mystery. There was a 3rd switch that was hidden behind a wine rack. The electrician that installed stuff in my house must haven been on crack when he put stuff in (My brother-in-law who is an electrician said "He must have been a real @#%#% because there's no reason your wiring should be laid out like this"). The electrician put in 3 separate gang boxes (not a 3-gang box, 3 separate boxes) for switches - one above, one below and one two studs over. Honestly I'm surprised that it passes code because it controls the over head lights to the room.

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    Maybe there is another one covered over somewhere. How many wires are in the other switch? – wallyk Jul 5 '14 at 18:43
  • The other switch has 2 blacks, a red and a ground. These are only the ones wired to the switch - there are white ones that are wired to each other but not the switch – 2 Left Thumbs Jul 5 '14 at 18:56
  • Did the first switch have four connections on it (four terminals), or three? If it has only three, the extra black is for chaining power onto the next device (outlet or switch) and you have a pair of 3-ways. – wallyk Jul 5 '14 at 19:16
  • Switch A has 2 Blacks and a Red connected. Switch B has 2 blacks and 2 Reds. Since all 4 wires are connected to the switch, how is it chaining power as it might potentially be turned off? – 2 Left Thumbs Jul 5 '14 at 19:26
  • What I also don't understand is that the single gang box that has switch A has 3 2-wire romex and one 3-wire romex going into it. Switch B just has 2 3-wire romex in it. – 2 Left Thumbs Jul 5 '14 at 20:05
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That IS a 4-way switch which means you do have two other 3-ways. The wiring you have can't mean anything else.

A standard 3-way dimmer cannot be placed in this location.

  • Assuming you're correct (which is what I believe) then where is the 3rd switch? I've been in this house for 5 years and flipped all of those switches and there's only 2 switches that control those overhead lights. – 2 Left Thumbs Jul 6 '14 at 19:28
  • Obviously can't tell from here, but the way it's wired it can't be any other way, unless of course someone removed the other 3-way and spliced the wires through in a hidden junction box. – Speedy Petey Jul 7 '14 at 19:33
  • What would it look like if it were spliced through in the hidden junction box? Is that maybe the mystery 4th romex in the Switch A box? Assuming that it is just spliced, is it possible to put the 3-way dimmer in where switch B was? – 2 Left Thumbs Jul 8 '14 at 0:35
  • @2LeftThumbs If it were spliced in a hidden junction box it would look exactly how it currently looks. – Brad Gilbert Jul 8 '14 at 22:31
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    If there is a hidden 3-way, or fixed wiring that replaces it, you could put a 3-way in this position, as only one of the travelers from the 3rd location would ever be live ... but it would possibly create confusion later. It would be best to find the 3rd location and figure out what's going on there. Perhaps a switch was moved during a remodel, is in a closet, or behind an appliance? – TomG Oct 4 '14 at 19:13
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As Speedy said, your wiring is indeed characteristic of a four-way switch. Four-way dimmers are not a COTS item; however, you can put a dimmer there with the help of a 3-position, 2-pole (DPDT) wall switch such as this Hubbell-Bryant 4825I, mounted in a dual gang box and wired as in the following diagram (travelers are black and red, grounds are green, neutrals are gray, and in-box jumpers are blue, but you can use any color for those save for white, gray, or green:

A way of wiring a dimmer into a four-way circuit with the aid of a DPDT switch -- not quite equivalent to a four-way switch, but it's the closest I could come with typical mains-wiring parts

Do be forewarned though that the results of this aren't quite the same as a regular four-way switch: in particular, if you flip the switch fully at this location, you won't be able to turn it on at one end without flipping the switch at the other end as well. (I might come up with a better answer -- but it'll take me a while to fiddle with things, and 4PDT wall switches aren't a thing, either -- can you use a suitably rated electronics-type toggle switch in mains wiring?)

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While the partial solution in my earlier answer does provide at least some dimming functionality at a four-way location without replacing the switches at all locations with multi-way communicating dimmers and matching companion devices, it is possible to construct a true four-way dimmer from a single-pole, three-wire (switched/dimmed hot) dimmer and 3 SPDT relays.

However, this requires:

  • A single-pole, three-wire dimmer such as the Lutron Skylark SF-10P
  • A dual SPDT relay such as the Functional Devices RIBU2C
  • A single SPDT relay such as the Functional Devices RIBU1C
  • The presence of a neutral (grounded) conductor in the switch box -- if there is no neutral, do not proceed with this approach
  • A 1/2" and a 3/4" conduit knockout in the box or extensions thereof
  • and a whopping 61 in3 of box space, worst case -- this will require either the replacement of an existing single gang box with a square box and matching 2.125" deep extension box or the use of 2 extra gangs of masonry-type or device-type box atop what's needed for the existing devices.

Wiring diagram of the setup

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