I intend to install motion-activated lights outside a garage (there is a breaker panel with available capacity for lighting).

I can run regular NMB #14/2wG wire within the open walls or down from the eaves. I know to use a waterproof junction box. What's the best way to get the wire into the box without exposing the cable to UV light or to moisture? I'd like to keep it simple, avoiding conduit etc.

My thought is to drill an oversized hole in the wall and put a waterproof cable bushing on the box's back knockout. The wire won't be exposed and would be behind a waterproof box, around which I'll caulk. Is this a safe and economical approach?

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    Connectors have to have a UL equivalent approval. Since NM is not approved for "damp" location nobody can get approval for a waterproof connector. Where I work NM cable or it's wires cannot break the vertical plane of exterior wall, even in exterior conduit or weather proof boxes. I can recess a box into the wall and use NM. Jun 6, 2021 at 23:57
  • Don't they make a wet rated NM? NMWU? Jun 7, 2021 at 0:18
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    OP is in GA, I should have prefaced my comment with "In the US..." NMWU (Canada) is not recognized by the NEC. He could use UF, but ooph, it's hard to work with. Jun 7, 2021 at 0:47

2 Answers 2


To do it correctly to code, you need to transition to a wet rated wire type inside the building before going outside the building to a wet-or-damp location. All exterior conduit is defined as (and normally is) a wet location, from condensation if nothing else. Thus, being a "waterproof" box is not quite what you think it means. It's not uncommon to need to add a drain hole for the condensate...

That's as easy as a junction box inside with a short conduit nipple to outside and some THWN wires.

Grab some "duct seal" putty while you are at it to pack around the wires entering the conduit to keep inside and outside "more separate." That helps to keep air prone to condensing from traveling through the conduit to the inside box, and perhaps also bugs, etc.


Is your garage framing open to the inside? If so, the most common way to do this in New England would be to staple NM cable down along a stud, then feed it through a small hole in the wall into the back of a box. The box could be an old-work box recessed into the siding or a surface-mounted weatherproof box.

As others have noted, it can be questioned whether the outside box and the transition though the siding counts as a dry location. Nobody would care here, but they might in other parts of the country. If your area requires a permit and inspection, perhaps you could call the inspector and ask.

  • What you described is what I had planned. I had a question about how to mechanically secure the wire where it enters the back of a surface mounted box. That’s where I proposed using a water tight cable bushing. The inside of a surface mounted waterproof box being considered a wet area was a surprise to me. It seems like the simple approach might be safe, yet not be permitted by the code. Seems like an “edge case”.
    – jbbenni
    Jun 7, 2021 at 11:07

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