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Please be patient folks, this is the first time I've tried asking a question here :-)

I use full conduit wiring (usually 3/4" EMT) for new stuff in my shop/garage areas. The new stuff sometimes has to connect to NM cable wiring. I usually formally transition to my new EMT conduit wiring in a metal box, with the NM coming in thru a knockout and clamp in a protected way (e.g., thru the back of a 4 square box that is surface mounted on a sheetrock wall).

But, this isn't always reasonable. So I have some questions about what is and isn't allowed when using EMT as protection for NM cable as it approaches a box.

  1. When using EMT for protection of NM cable, is it OK to attach the EMT sleeve to the box using a box connector, just as one would in full EMT conduit wiring?

  2. If attaching the protection with a box connector is OK, how is the requirement met for securing the cable within 12" of the box (as required in 334.30) if the EMT sleeve is longer than 12"? Is the EMT sleeve itself considered as "securing and supporting" the NM, provided the EMT is itself properly secured?

I understand that the NM must be secured with 12" of the entry to the sleeve, I'm asking about the other end, where the NM passes into the box. I'm asking about the general case of cable entering a typical junction box, I know there is a special rule for entering an electrical panel thru a sleeve.

  1. Is there a requirement to clamp the NM if it enters the box thru a sleeve? I can see how this could be done with an interior clamp integral to the box (e.g., an old style metal gangable device box), but a typical knockout clamp couldn't be used because the EMT adapter would preclude that.

It feels like if there is no clamp as the NM comes in, then we've really already transitioned to conduit wiring, which means we really don't have a sleeve anymore, it's now conduit.

  1. Would using a NM/EMT transition fitting when the NM first enters the EMT sleeve (more than 12" away from the box) make any difference at all? Are these fittings ever required, and if so, for what? You can't just strip the sheath from NM and go into conduit wiring with them, because the conductors in NM aren't suitable for conduit wiring as they aren't intended for pulling, wet environments, etc as THHN or XHHW would be. So what the heck are these NM/EMT fittings used for?

So thanks for any insights you can offer, I've seen a lot of really thoughtful responses from the folks that hang out here.

1 Answer 1

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If you put a NM clamp on the cable entering the conduit, after that point the cable is in conduit, where wires and cables don't need to be clamped, because they are protected by conduit and can't be yanked on. Securing NM is needed when it comes into a box and then transitions out to the world exposed to whatever might want to hook onto it and pull.

So, yes, the EMT sleeve should use a normal connector to the box.

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  • thanks for the quick reply. So it sounds as if I should just secure the NM when it enters the sleeve (one way could be an NM/EMT transition clamp), then attach the other end of the sleeve to the box with an EMT box connector, leave the sheath on the NM all the way thru the EMT until it enters the box. Then secure the EMT properly to the wall, and that's it. No matter how far the NM runs in the EMT, no support is needed except securing at the sleeve entry point. Do I have that right? It sounds right and sensible to me, but it sure seems hard to tease that out of the NEC :-).
    – tekrefugee
    Jun 1, 2023 at 21:48
  • NM is a wiring method consisting of NM cables that need to be stapled and clamped. Conduit is a wiring method where wires (or cables) don't need to be clamped. You are transitioning the cable from one wiring method to the other.
    – Ecnerwal
    Jun 2, 2023 at 12:01

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