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I'm interested in replacing an existing outlet (in a wall that's finished with drywall) with a two-gang duplex (four outlets total), using an "old work" box. This box is located in the garage, so I'd like it to be sturdy.

Is it considered good practice to screw the box sideways into the stud?

Photo and diagram of old work 2-gang box

It appears from another forum that this might violate electrical codes. In the US, where I am:

NEC 314.23. Supports. (B) Structural Mounting. (1) Nails and Screws. Nails and screws, where used as a fastening means, shall be attached by using brackets on the outside of the enclosure, or they shall pass through the interior within 6 mm (1/4 in.) of the back or ends of the enclosure. Screws shall not be permitted to pass through the box unless exposed threads in the box are protected using approved means to avoid abrasion of conductor insulation.

If so, is there a better way to support old work boxes than just relying on the drywall tabs?

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    In general, if you can screw into the stud, you don't use an old work box. In other general, blue plastic boxes - ugh. When I was an ignorant teenager, sure. Now, no. Steel is good.
    – Ecnerwal
    Commented Apr 11, 2021 at 12:42
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    If you want to talk about electrical code, you have to talk about where you live. In Canada boxes come with holes to screw to studs, both inside and outside the box. The way this is worded "pass through" the box makes me think of an old installation style where long nails or screws were driven right through the box and into the stud, which is a huge pain to work around, but also easier to remove for rework than external fasteners. Arguably the wall you want to drill through is an end of the enclosure, so the head of a fully driven screw would be within 6mm of it. Not my code though.
    – K H
    Commented Apr 11, 2021 at 12:56
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    The purpose/advantage of an old work box is that you use it where there is no stud to attach to. The tabs bind it to the drywall. If you use the tabs then you do not need to screw it to a stud. IF you have a stud to attach to then you would use the box that jack recommends in his answer.
    – Alaska Man
    Commented Apr 11, 2021 at 18:36
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    I installed a number of double- and triple-gang boxes like that when we initially updated the wiring in our house. I've had no problems with either outlets or switches feeling wobbly. Of course, I've got plaster & lath walls, so it's stiffer than just drywall, but, depending on exactly where the box hits, there's a fair bit of play available if it's just plaster supporting the ears. I really haven't had any issue even with those boxes. If you were to have any wobble, it would most likely be on the end away from the stud anyway, and your screws wouldn't help that.
    – FreeMan
    Commented Apr 12, 2021 at 17:11
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    There's no issue with plastic boxes, ignore the vague FUD about them in the first comment.
    – TylerH
    Commented Apr 12, 2021 at 19:09

4 Answers 4

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Junction boxes are not to have additional holes drilled into them for securing them to studs. The box you have shown can be used and mounted fairly secure if you take the time to cut the opening as small as possible so the box tabs have more drywall to support it.

A better solution is to get a box similar to the one below with side screws already included to be mounted to the stud. This is the same size as the old work box but allows you to screw directly into the stud.

enter image description here

Southwire Smart Box 2-Gang Adjustable Depth Device Box #MSB2G

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    JACK: I'd forgotten about those, that's also a good option and a much faster install than my answer. Still, though, I think my solution would result in a more rigid mount....the question then becomes, how important is a bit of flex vs. the additional time and effort of my solution. Up to the OP. +
    – George Anderson
    Commented Apr 11, 2021 at 14:59
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    @GeorgeAnderson I think these are relatively new on the market as I don't remember seeing them when I was working. I recently used one for a utility outlet changing my dryer from three prong to four prong just to keep Harper happy :-) The box had very little flex and that was eliminated with the cover. I have used your solution many times but added a few drywall screw so I didn't have to wait for the glue to dry. +1
    – JACK
    Commented Apr 11, 2021 at 15:17
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    Thanks JACK. That works too. The only reason I suggested glue was to prevent the need of patching over additional screws in the drywall...which would be visible. LOL regarding keeping Harp happy! Take care.
    – George Anderson
    Commented Apr 11, 2021 at 16:02
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    In other words, get a new work box rather than an old work box...
    – TylerH
    Commented Apr 12, 2021 at 19:07
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    @Jack this doesn't apply worldwide, so could you add the electrical code or jurisdiction it applies to? I'm sorry you're not allowed to attach boxes this way. Do you have to put up with non-beautiful non primary colored wire as well?
    – K H
    Commented Apr 13, 2021 at 1:41
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No, and you'll crack the box if you try.

Plastic is not metal. Plastic boxes are flimsy things. They don't have any strength except where they have been gusseted specifically to have strength.

This means you cannot simply add mounting points anywhere on the box. The box will simply crack there, either from the violence of a self-drilling screw, or the stress points from a drilled hole clamped by a tightened screw, or the physical strain of people wrestling plugs out of a stiff socket.

No, boxes of this type are made to be used exactly one way: placed in a drywall hole exactly the size of the provided template, and then clamp to the drywall using the ears on the outside and the swinging clamps on the inside. You are required to use that box that way, or not at all. NEC 110.3(B).

I quite agree "to the drywall" is a bad deal and will not withstand ordinary stresses of wrestling a 3-prong socket out of a new, quality (stiff) receptacle socket. I'd find another way.

Try steel

If you want to 'freestyle' mountings like this, it's time to move over to steel boxes. Steel has the strength to allow you to drill holes where you please and use them for mounting screws. Steel is also vastly superior for every purpose of a junction box (containing arc fires, not melting and letting a fire spread, causing loose or arcing wires to trip the breaker).

It even self-grounds switches and certain receptacles, so one less wire to wrestle. Really, in a metal box you attach your cables' ground wires to the box first and push them all the way into the back of the box, and never touch them again.

For old work, you need to select a box that has internal cable clamps. This will also have fewer knockouts which makes it easier to find hole locations.

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    Many (most?) plastic boxes are of a more flexible kind, and don't cracky that easily. Although I tend to use a drill bit intended for woodwork for drilling holes in plastic. Then a truss-head or pan-head screw, maybe even with a washer to spread out the pressure.
    – einpoklum
    Commented Apr 11, 2021 at 21:37
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    The most common j-boxes (read cheapest) are the soft plastic variety. My father-in-law loves to screw those to the joist and they take to it decently well. I would imagine the fiberglass hard shell variety would not fare so well.
    – Machavity
    Commented Apr 12, 2021 at 19:51
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    The flexibility is part of the problem @einpoklum. If you use improper attachment points that are not gusseted, the box will at the least flex and shift, meaning your box is moving around while you wrestle plugs in/out of a stiff socket. That in turn can result in cracking at the stress points added through drilling. Plastic, as a material, is simply not metal - and UL has not tested or approved these boxes for field modification.
    – Harper - Reinstate Monica
    Commented Apr 12, 2021 at 19:55
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    @Harper-ReinstateMonica: Isn't "gussetting" for corners? Or do you mean some kind of reinforcement plating or extra plastic around the attachment point? Anyway, I'm just not used to seeing metal electric boxes.
    – einpoklum
    Commented Apr 12, 2021 at 20:01
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    And you did even say "certain" receptacles, but in my experience, those receptacles are super rare and I wouldn't want someone to get the wrong idea. The ones that don't self ground appear to self ground is the problem I see. I'm not going to mess with art, but if it appeals to you, you could say "special" receptacles rather than "certain" receptacles.
    – K H
    Commented Apr 13, 2021 at 3:10
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When I've had to do this, here's how I did it: Cut the new opening to size for the new box. Then cut 2 pieces of 1/2" plywood about 2" x 8" or so. Apply glue and slip them into the opening above and below with the edges aligned horizontally with the edge of the top and bottom respectively. Clamp in place until the glue dries. Then use a box with plaster ears (flanges) using them to screw into the sheetrock/plywood. I'd mark the holes and pre-drill because if you bust out the plywood, you'll have a real mess on your hands! It's a little time consuming, but turns out a great result.

Your other option of course is to simply cut out the sheetrock from one stud to the other, install a new work box and repair the sheet rock, but I don't think that's what you want to do.

BTW, just screwing inside the box to the stud will result in a lot of movement of the box when plugging in and unplugging cords. Don't ask me how I know this! Did it once, never again.

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Buy a better box if you want it to be sturdy. Partially because there's a shortage, I couldn't buy a 2-gang old work plastic blue box like the one you pictured in the question. Nearby, there was a much pricier fiberglass box that came with metal tabs.

Fiberglass old work box

Not only will that box grip anything, it doesn't warp at all. The next step up from there would be a metal box, but that might require clamps and other things to get the wire safely in (plus you need to bond metal boxes).

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    In some areas you can just buy metal old work boxes if you don't want plastic, which likely cost less than this super fancy fibreglass one I've never seen. There are actually 3 different styles of metal old work box you can get where I live, 4 if you include F clips. Here the plastic one costs a few cents more and isn't available in every store. Having to ground metal boxes is more advantage than disadvantage as they come with 2 or more ground screws, each of which can fasten 2 ground wires, so you often don't need a wire nut or Wago and you get some free box volume as a result.
    – K H
    Commented Apr 13, 2021 at 1:51

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