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I replaced the single-gang switch box on this basement stairwell stud with a double-gang (shown) so I could add a second switch. I also plan to upgrade the conduit from 1/2 to 3/4” so it’s not overfilled now. My question is - is the bigger box still NEC compliant in this location, given that it’s twice the width of the stud it’s attached to? Thanks!

enter image description here

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    Regardless of NEC, you are going to hit that multiple times with your shoulder or arm over time and curse yourself repeatedly. Go for a double/triple switch in a one-wide box.
    – Jon Custer
    Feb 7, 2023 at 14:59
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    Think the problem is more of the placement than the size. People will keep smacking into the edges on the stairs and walking on the floor. Would be better to place it flat on a wall. That box is probably the wrong type for switches also.
    – crip659
    Feb 7, 2023 at 15:00
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    Box (with appropriate cover plate) is fine for switches, but placement is indeed wrong, and as noted 1/2" conduit is more than adequate if you use THHN rather than NM/B, but if using conduit as a protective sleeve, there you are stuck with NM/B in conduit.
    – Ecnerwal
    Feb 7, 2023 at 15:34
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    manassenkatz has it right, but I would add it is not a duplex box, but a junction box. No way to mount switches in that box.
    – fogmann
    Feb 7, 2023 at 15:42
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    Now that you have it, you could mount it on the back side of that stud turned sideways and flush with the stud on the stair side. In the way switches are normally installed at the ends of stairways. It will protrude very slightly in the back, which is the right side of this picture.
    – jay613
    Feb 7, 2023 at 17:52

3 Answers 3

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I tend to agree that, given how exposed it is, it's likely going to become a nuisance and/or get ripped off the stud. There's a couple of ways to play this

Double switch

Double switch

These take up a single gang and accept any normal receptacle cover (I would highly recommend going metal for this). It looks like you've got two cables, so break out the tab on the side if it has one.

Two boxes stacked vertically

This might be more trouble than it's worth, but it would still get you a low profile. Buy two single gangs and two EMC connectors. Cut a short length of EMC and connect the bottom of the top box to the top of the bottom one. It's still allowed, and you can use stripped cable to run the extra length.

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  • Thanks Machavity! I like the double switch idea; the only problem is that one of my switches is a 2-way.
    – Michael D
    Feb 7, 2023 at 17:15
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    @MichaelD Ah. Well, fun fact: if you hook your switch up with only one of the travelers then it acts just like a single pole switch. And single-pole/multiway switch combos are a thing
    – Machavity
    Feb 7, 2023 at 17:17
  • Box fill is likely to be a problem, especially if the original box was the dreaded "handy-box" that just barely manages enough volume to allow fill for one device.
    – Ecnerwal
    Feb 7, 2023 at 17:22
  • @Ecnerwal Fair point. A deeper box might be needed
    – Machavity
    Feb 7, 2023 at 17:26
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As noted by others in comments, the problem is that people will bump the switch box on the way up the stairs. Mount it using the left knockout instead of the middle and you should be fine.

If you are, as I suspect, using conduit to provide protection to the cables but using the cables outside of conduit once they get to the ceiling, that's fine. If, however, you are actually running conduit all the way from the panel to this location then you should seriously consider switching to individual wires instead of cable. With metal conduit you don't need the ground wire, so for two switches that's at most 6 wires - and only 5 if the switches are on the same circuit so that they can share neutral. With individual wires (e.g., THHN) you are fine with 1/2" metal conduit. Except: if (as appears to be the case here) you use cables most of the way and then switch to conduit, you can't share neutral wires because the neutral current would not be properly balanced once on the cable portion. On the other hand, if you don't actually need neutral then you can leave it out and add (one or two, as needed) in the conduit section later if needed (one of the advantages of conduit).


A picture in another answer shows a double-switch that is actually a double 3-way switch. It isn't clear what kind of switch you already have and what you are adding. In the past, a 3-way switch could use /3 cable with several different possible wiring schemes. However, current code generally requires neutral in the box and so things get a bit more complicated. Your existing switch should be grandfathered, but for the new switch this could be an issue. In any case, if you use conduit with individual wires then you can't remark white as a traveler or hot wire as you can with cable, you must use white only for neutral. On the other hand, with conduit you don't need to provide neutral if you don't need it, but that may not really apply when conduit is only part of the circuit - i.e., the cable portion would still need to include a neutral wire for new switch boxes, so then you might as well bring the neutral all the way to the switch box.

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  • Thank you! Conduit is being used to run wire down from the rafters. I will use the left knockout or move the box to the right side of this beam so that people don’t hit it when walking on the outside of the stairwell. Would that placement be NEC ok? Presumably since it’s still at the opening of the room.
    – Michael D
    Feb 7, 2023 at 15:43
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    That is an old problem - even more familiar to computer network people like me (I do that as part of my real job, electrical is amateur so only in my own home). Put tape on the wires before you feed them down and then tape the other end to match. Easiest is add either blue or yellow (because neither will conflict with black, red or white) on one cable sheath and on the individual wires for that switch. Feb 7, 2023 at 15:48
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    Oh, dang, you're right! My math was off. Ignore me, comment deleted.
    – FreeMan
    Feb 7, 2023 at 16:40
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    @manassehkatz-Moving2Codidact I know that (at least as shown so far) this isn't, but "maximum number of wires for two switches" was mentioned, (since deleted) and that would raise the spectre of "if they were 4-ways..."
    – Ecnerwal
    Feb 7, 2023 at 16:47
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    @manassehkatz-Moving2Codidact An ancient trick for helping to sort out wires/cables is to loop the wire/cable when determining the length needed, then pull the end of the loop through and cut the loop end to separate the circuits. The text on the wire/cable will run in opposite directions. It won't resolve all issues if you have six black wires, but it is sometimes handy when sorting out existing wiring.
    – HABO
    Feb 7, 2023 at 17:59
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Evidently some of the folks commenting and answering have never seen how you mount devices in a 4 or 4-11/16 square box. The box appears to be a normal 4 inch square box, probably the 1.5" deep flavor. It's not actually a "2-gang" box at all, those differ in details, but a 4-inch box will accept two yokes.

A plaster ring for two devices:

Plaster ring two-device cover image from grainger

An exposed work cover for two decora devices:

2-decora exposed work cover image from gordon electric

Exposed work cover for one duplex device:

1-duplex exposed 4-inch box cover image from garvin industries

Two-switch 4-in exposed work cover:

Two-switch 4-in exposed work cover image from gordon electric supply

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    Very valid point (I've got a stack of the double-gang in the top pic, and a bigger stack of single gang), but not an answer to the question asked... ;)
    – FreeMan
    Feb 7, 2023 at 16:36
  • Learn something new everyday.
    – crip659
    Feb 7, 2023 at 16:36
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    @FreeMan Yes, this is really a "glorified comment because comments don't have pictures." I freely admit and accept that, as there was already a perfectly good answer to the question.
    – Ecnerwal
    Feb 7, 2023 at 16:42
  • Valid-ish. This box is nominally the size of a double-gang box and the term serves as a convenient size reference. This is not an answer.
    – isherwood
    Feb 7, 2023 at 19:41

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