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First time homeowner and newbie DIY-er here.

I'm replacing the light fixture in our bathroom and there's no junction box behind the wall, but I think I'm seeing insulation in there too.

There's a stud directly to the left of the circular hole (where the previous fixture had two screws into the stud, and two screws into the drywall).

Do I need to put a junction box in there? It seems unsafe not to.

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  • @isherwood I saw that post, it's similar, but I don't think it's completely applicable to mine. But maybe I'm too much of a beginner to know the difference. – David Apr 20 at 16:13
  • The answers on that question don't mention it, but it is legal to use the fixture housing as a junction box if it's suitable. You'd need a strain relief device at the entry point. In many years as a home builder this was commonly done. – isherwood Apr 20 at 16:13
  • Here's another: diy.stackexchange.com/questions/141398/… – isherwood Apr 20 at 16:14
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    More: diy.stackexchange.com/questions/154803/… The point is that you probably should retrofit a box, but it's not necessary in all cases. – isherwood Apr 20 at 16:15
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    Gotcha, thanks. I'll try to find a box that fits. – David Apr 20 at 16:16
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The big unknown is the state of the wiring behind the drywall. If it is in conduit (unlikely) then you are in better shape because you can run new wires if you need to. More likely is that this is a cable. If there is enough loose cable inside the wall that you can actually have cable (i.e., outer-sheath still attached) pull through the hole in the drywall, then you can either use a surface-mount box or use a fixture that has a box built into it - i.e., pull the cable all the way into the fixture.

However, if the cable (outer sheath) ends behind the drywall with no extra length available, then you have to cut into the wall and install a box. If the cable (outer sheath) ends too far behind the wall to get it into a box at this location then you have bigger problems.

Assuming the cable sheath ends within a few inches of the wall, you should be able to cut a hole to match a box and install a box. The left edge should be at the stud - mount the box to the stud. The cable will need to go into the box so that the outer sheath fits through a proper clamp. On plastic boxes these are usually part of the box. On metal boxes these are additional (they don't cost much, they just aren't included because a metal box used with conduit will not need them, plus sometimes you need more than one, depending on how you are using the box).

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  • Very helpful, thank you! – David Apr 20 at 16:27

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