What to do when the wires barely fit in the box? We got them to fit with a lot of fusing, but I'm not sure if that's okay or not. Lots of smushing down and the outlet covers don't fit flush on some. My concern is twofold - that getting all the wiring in there as fiddly and bent to make it fit will somehow make a dangerous situation. And if we just did it outright wrong and that's why it's not fitting.

Part of the problem: using GFCI outlets, surface mounted PVC and plastic boxes because this is in a wet location and I couldn't find any other boxes that were appropriate. 20amp circuit, so the wiring was fairly stiff.

Specifics: Big project this weekend to wire a fish room. As it is to be around water, went with pvc and plastic gang boxes and gfi on each outlet (at a wince-worthy expense) With the help of a friend who is not an electrician but has done a lot of cabling and electrical work, we installed 2 20amp circuit breakers in an empty panel, and 11 boxes with 22 GFI outlets using romex 12 gauge. I think this was the first time he worked with 12 gauge wiring though. We were actually able to make most of them fit, but there is a lot of wire in each box, and some of the outlets are sitting at odd angles because of the way the wire was put in there.

It might be fine, and with some more finessing get the ones at angles in there the rest of the way. But I want to verify it's okay, and if its not, figure out where and how to get deeper boxes to be used in a wet area. (I did see plenty of deeper boxes but not in an area that was meant to be surface mounted and weather resistant).

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    I understand it might be too late, but you could have used one GFCI receptacle at the beginning of each run, wiring the ordinary receptacles to the "load" side of the GFCI receptacle. They would still all be protected. Dec 18, 2014 at 17:44
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    See diy.stackexchange.com/a/33077/4207 for the NEC box fill chart
    – Steven
    Dec 18, 2014 at 18:12
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    I did each one separately because it's for aquarium systems, and if one pops, I want as many others to keep running. More expensive, but if one fails, it won't kill the life support system on the rest of the systems.
    – Tami
    Dec 18, 2014 at 19:30
  • Steven, looking at the gang box chart and I dont understand what a conductor is. Is it just a wire? Something else?
    – Tami
    Dec 19, 2014 at 7:57
  • @Tami Yes, a conductor is just a wire. :-) Dec 19, 2014 at 8:43

2 Answers 2


One option is to use a single gang mud ring for double gang box.enter image description here you can get metal or plastic ones.


You can definitely get deeper boxes, and you can also get box extenders, but at some point you'll be limited by the depth of your walls and you'll need to use double-gang boxes to get more room.

Since you commented that you're using a separate GFCI for each fish tank, I presume that you're pigtailing the wires through the boxes, and not feeding downstream GFCI's through the upstream GFCI's?

Somebody else already mentioned the box fill chart in a comment. You can also find handy little box fill calculators on the web.

EDIT: The answer that suggests using a single gang mud ring for a double gang box is spot on, that's what I meant by going to double-gang boxes, and you can certainly get the mud rings in metal or plastic.

You can also get single-gang boxes with a behind the wall cavity to one side:

enter image description here

Are your walls open so that you could replace the boxes (relatively) easily with double-bang boxes? If you've already put the sheetrock up but haven't taped it yet, you could unscrew it and replace the boxes. If you use double-gang boxes with mud rings, just fill the gaps beside the boxes (where you cut the holes in the sheetrock bigger) with joint compound and tape over them.

  • Yup, they are pigtailed. That is adding to the wire volume in each box. I have been searching high and low for deeper surface mounted boxes, and have not found them. The extenders I've seen appear to be for metal boxes? But I need to get a closer look to see if they'll work.
    – Tami
    Dec 19, 2014 at 9:41
  • Are you able to extend the boxes without them sticking out of the walls? If your walls are still open, I'd just put in double-gang boxes with mud rings, works great, leaves you with a single-gang face plate, and lots of room inside the boxes. Dec 19, 2014 at 17:06
  • You can definitely get single-gang plastic box extenders, too. Although they are typically intended for extending a box back out to the wall surface when you put tilei or some other material on your wall, which causes the boxes to be recessed, which of course violates code because the box must come all the way out to the faceplate so that electrical connections aren't exposed directly to building materials. Dec 19, 2014 at 17:15
  • Walls are not open. These are surface mounted using pvc conduit and plastic weatherproof boxes. This is the box: menards.com/main/mobile/electrical/rough-electrical/…
    – Tami
    Dec 19, 2014 at 18:47
  • Went with pvc for the weather resistance, but that box is the only one I could find at a few different hardware stores. It does all fit, but just barely. I think in part because of the depth of the gfci outlets. Because of the pigtailing, I think that would make 9 conductors in that box? If I understand the box conductor chart, which I might not)
    – Tami
    Dec 19, 2014 at 18:51

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