My jurisdiction requires AC/MC cable (NYC).

Every time I deal with an exterior wall penetration (or see one in progress) for a surface-mount box, it looks roughly like the attached photo: hole drilled through wall, then bare MC through the wall.

Photo of MC cable through exterior brick wall

  1. How would this be attached to the exterior weatherproof box? They have a hole on the back, but it's a threaded connection (like for screwing in RMC), not a knockout. Even if it was, there's no room for the connector behind the box.

  2. How would the cable be secured on the interior side of the wall? Just MC strapped down?

I can imagine the typical answer is "just strapped down on the inside and just the conductors fed through hole in the back of the box with caulk around the box edges", but even if that's the "standard" builder/DIY answer to the above, what would be the correct to-code way?

2 Answers 2


When surface mounting a weatherproof box, I've always run rigid or EMT through the wall and terminated the armored cable on the inside wall in a junction box and then run individual cables from box to box. Most MC isn't rated for outdoor/wet locations so that's my reason for doing it this way. Got burned once in Chicago for extending armored cable outside. Sometimes it's easier to chip away the brick and recess the box.

  • 1
    Yeah, even if you were using PVC-jacketed (i.e. outdoor rated) MC, the required fitting to terminate it into a Bell box would stick out well into the wall. Commented Sep 7, 2023 at 2:12

Correct to code as I understand it (and it's not blatantly clear that this won't, in fact, fit - the hole is not tight to the cable)

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is into a listed clamp in the back of the box. Presumably one of the less bulky versions, unless you like chipping holes bigger with cable in place.

  • But what would that connector be? The back of a weatherproof box is threaded, not a knockout. And whatever that connector might be, it would probably be massively bigger than the hole, not mildly so. Commented Sep 6, 2023 at 22:29
  • The threads on a clamp to go into a knockout are compatible with the threads in a box. Take the nut off, screw it in.
    – Ecnerwal
    Commented Sep 6, 2023 at 22:32
  • 2
    @T.J.Schuck you might be missing that you can put the clamp inside the box rather than outside of it. Then the only part poking out of the box is the cable itself. It's not always helpful to run them 'backwards' like that, and they count against fill, but it works just fine and can be super useful in this sort of scenario.
    – KMJ
    Commented Sep 6, 2023 at 22:44
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    That is not generally true for a threaded weatherproof box, @KMJ. The inner end of the threads is not accessible.
    – Ecnerwal
    Commented Sep 7, 2023 at 1:39
  • 1
    I put one in for a low voltage cable just a few weeks ago and had no issue threading into the inside of the box. The threads were accessible. I didn't depend on the connection for waterproofing, and did that using caulk behind the clamp and the usual ring with weep holes against the wall. I was using something like this: homedepot.com/p/…
    – KMJ
    Commented Sep 7, 2023 at 3:42

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