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I have a house with an attached garage. On the garage wall that faces the interior of my home is a porcelain light socket with a light bulb screwed in that is switched on and off by a switch mounted nearby on the same wall. My garage has drywall. I unscrewed the light socket plate from the drywall to peak what's underneath. What I found was a 1/2" deep, 3 1/2" diameter pan box and I could see the pan box is mounted directly on OSB. The OSB has a hole drilled out and NM wiring is coming through the OSB hole into the center of the pan. Behind this wall on the interior is a laundry room and I know the garage light is on the same circuit as the ceiling light fixture for the laundry room.

Is this up to code? I don't know if this garage light socket was installed by a licensed electrician when the house was built or if it was a DIY job by the previous homeowner. I suspect it was original to the house, but I'm used to seeing junction boxes mounted to 2x4s instead of an OSB sheet directly behind drywall and I just want to confirm this ok and something an electrician might do for an attached garage on a wall shared with the interior of the house?

Picture attributed to The Spruce / Margot Cavin. Round pan box - The Spruce / Margot Cavin

Porcelin Leviton lamp holder

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As long as the box is securely mounted, then it's OK. The problem is that the MN cable coming through the OSB and directly into the box. That's a No No. You need a NM cable to box connector to fasten the cable securely to the box. So just turn the power off, remove the fixture, unscrew the box from the OSB, add the connector to the box, put the cable through it, tighten the screws to secure the cable and remount the box. You might have to enlarge the hole in the OSB to make room for the connector.

Here are two examples of the type of connectors you could use.

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  • Alright, thanks for the information. Could you clue me into what kind of cable-to-box connector is appropriate for a pan box? I'm hoping enlarging the hole isn't necessary because I don't see how to do that without risking damage to the NM cable. I suppose if it's routed through the attic I could pull it up into the attic then fish it back down after the hole is enlarged.
    – acker9
    Mar 2 at 20:08
  • The plastic bushing/clamp shown in JACK's answer is appropriate for ANY metal box with the appropriately-sized hole. It would require only the slightest (if any) enlargement of the OSB hole, done with a few strokes of a file/rasp. The bushing just gets snapped into the knockout hole in the box, and the NM cable pulled through. There is no danger of damaging the cable doing that. Metal boxes can be attached to just about any solid surface: plywood, OSB, sheetrock alone, as long as appropriate screws/anchors are used.
    – kreemoweet
    Mar 2 at 21:35
  • I did go to the home improvement store and found the plastic bushing shown in JACK's second picture (thanks!). It would have worked wonderfully except the sheathing on the NM cable was stripped down too much, almost flush to to the OSB (sigh). I realized this late. After attempting to put the bushing on, I realized this was doing more harm than good, probably biting into the wire insulation. I removed it. Moral of the story: The bushing works great, but it is designed to fit over the sheathing and you need enough of it exposed for it to work out in your favor.
    – acker9
    Mar 3 at 0:57
  • @acker9 minor repairs to sheathing can be done with white PVC tape. About 3..5 layers over the length required would suffice here.
    – P2000
    Mar 3 at 20:46

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