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enter image description hereenter image description hereSingle three way switchthree way switchesI have two three way switches operating two different lighting circuits in a 2 gang box. Power feed for both circuits is in the same box. Is there a way to combine both circuits and replace the two 3-ways with one 4-way switch?

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    Conceptually: Left box = lights 1, right box = lights 2, middle box = power in for 1 and 2. So the key question is: Do the common wires (switched hot) from left and right come back to the middle and go from there to the two sets of lights? Or does the common wires and neutrals extend from left to lights 1 and from right to lights 2? If it is the first (commons back to middle) then this should be trivially easy. If it is the second then it gets quite a bit more complicated. Switch box pictures showing wires/cables would help a LOT. Commented Mar 31 at 15:42
  • Please see pics.
    – Gary
    Commented Mar 31 at 18:20
  • two gang box has two three way switches. power comes into this box and is jumpered to commons on both switches, neutrals from both lights are wire nutted to the feed neutral.
    – Gary
    Commented Mar 31 at 18:26
  • There are two switches like the second pic. One for each light system. I'm confusing myself! This is a 3-way switch system at the top and bottom of my stairs that operates a light in the stair well. Another 3-way switch system at the bottom of stairs and the outside basement door that operate the basement lights. Power comes into the two gang box at the bottom of the stairs. I want one four way switch system. one switch at the top of the stairs, one at the bottom and one by the door. All switches will turn all basement and stairwell lights on and off
    – Gary
    Commented Mar 31 at 18:34

2 Answers 2

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Since this is all on a single incoming feed...

Since you have a single incoming power feed, you should be able to take the incoming hot, send it to one of the three way switches, then have the travelers come to a 4 way in the middle of the box, and then send them off to the other 3-way and get your load back from that to split to the two outgoing lighting feeds.

If this was two separate circuits...

Merging two 3-way switches for two separate circuits into a single switch is possible, but requires an actual DPDT switch such as a Leviton 1282, not a 4-way switch. Note that the 1282 has a center position that is totally OFF; this may be desirable, or simply something you'll have to work around.

You would also need to handle-tie the breakers for the two circuits together as per NEC 210.7, which may require moving breakers around in your panel:

If two or more branch circuits supply devices or equipment on the same yoke or mounting strap, a means to simultaneously disconnect the ungrounded supply conductors shall be provided at the point at which the branch circuits originate.

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  • I misspoke when I said two circuits. It is one breaker feeding the switch box and then power is jumpered between the switches so the breaker box will be fine.
    – Gary
    Commented Mar 31 at 13:51
  • I'm trying to find a wiring diagram for such an arrangement, could you provide one?
    – Gary
    Commented Mar 31 at 13:53
  • I'm trying to have one 4 way setup to turn on both lights. I want all lights to be off or on together
    – Gary
    Commented Mar 31 at 13:55
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    One breaker, power is split in switch box
    – Gary
    Commented Mar 31 at 15:26
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    @Gary -- updated, although photos of the insides of the switch boxes would certainly be helpful (don't have remote X-ray vision to see what's going on over at your place!) Commented Mar 31 at 16:38
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Based on comments, the three boxes are: top, bottom, outside. Top and outside each have a switch and an onward cable (switched hot/neutral) to lights. Bottom has incoming power and a switch & cable to top and a switch and cable to outside.

There are certain configurations where this might work without new cables. I don't think this is one of those configurations. The basic problem is that you have three wires (ignoring ground) between the various switch boxes. Two wires in each are travelers, which in theory could be travelers to a bottom 4-way switch instead of to a pair of three way switches. However, you also need:

  • Neutral going to each light fixture via top and bottom.
  • Hot going to one 3-way switch (let's put it to top).
  • Switched hot coming from the last 3-way switch (outside) to all the lights - which means a wire looping back from outside to bottom to top.

That means 5 wires (traveler 1/traveler 2/neutral/hot/switched hot) from bottom to top and 4 wires (traveler 1/traveler 2/neutral/switched hot) from bottom to outside. 5 > 3, 4 > 3 - so this just doesn't work.

If this were a new installation, it would be done a bit differently, but would still probably need either 4-wire cable or in some sections both a 3-wire cable and a 2-wire cable. There is no easy way to do this kind of retrofitting.

Smart Switches to the Rescue

The solution is to use smart switches. Put the "main" switch at bottom, replacing the two 3-way switches in that box. We know that has incoming power and cables to the other boxes. Rewire the cables so that you have a simple hot/neutral/switched hot to top and outside. Then, depending on the type of smart switch, you either put in a "battery powered remote that looks like a regular switch" or a powered remote that gets hot/neutral but doesn't actually switch any hot lines. Those two switches (top and outside) simply signal the main smart switch (either wirelessly, which usually does not mean WiFi, or over the power line) to toggle the lights in a manner similar to a traditional 3-way/4-way set of switches.

There are a number of different smart switch varieties available. I won't recommend one because (a) we usually don't do that here as such items change and so the answer becomes obsolete quickly and (b) I don't have any specific ones to recommend at the moment. But if you pick one and want to know if it will work, feel free to ask about specifics.

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