I'm running wire for a 70V audio system and there is a barrier wall in the way of my run. I was wondering if it is legal as far as NFPA 70 / NEC goes if I just poke a hole in the wall (non-insulated and hollow) and run the cable through that? The cable is CL2 so it should be rated for in-wall, but I have no idea if I should still get a piece of conduit to run the cable through.


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    What do you mean by "barrier wall" in this context? Apr 30, 2019 at 2:32
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    Cl2 is listed for use in 1 &2 family dwellings in other than air handling spaces (risers, ducts and plenum) nec725.179.c. So it can be run in the wall with or without conduit in your home. Note, in some cases I have had to use step up then step down audio transformers to kill ham & police/fire radio bleed over on my audio system in our riding arena the longer your wiring is the greater chance of having this problem but transformers can take care of the problem.
    – Ed Beal
    Apr 30, 2019 at 13:34

1 Answer 1


Commercial occupancy? In the US, the two main things you have to be aware of is penetrations in fire rated assemblies and cable jacket ratings for commercial low voltage. 70V speakers don't count as high voltage, it's the same rules as network cables (CAT5/6 or Fiber).

Typically commercial low voltage installers will use plenum rated CMP cables everywhere to simplify things, and then use intumescent fire caulking to seal any gaps in any wall penetrations in fire rated assemblies for small bundles of wires. Usually 3-4 wires or so.

In situations where they need many wires (10+) they'll put in a short piece of conduit, and use intumescent fire caulking to seal the outside of the conduit to the fire rated assembly, then put their wires inside the conduit, then stuff the hole with mineral wool insulation and/or intumescent fire caulking.

If this isn't a fire rated assembly, and you're using plenum rated cable, then pretty much anything goes. Doing whatever looks the most visually appealing and professional usually takes precedence, but that's probably because the rest of us don't really know the rules. I probably shouldn't suggest to do something just because everyone else does it that way though.

I can't speak to your CL2 cable though. In a residential abode you shouldn't have a problem unless that wall cavity is being used as an air return for HVAC, but in commercial everything above the ceiling is usually used for HVAC return air, so plenum rated cable is all that gets used so it's all I really know much about.

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    Hey Dotes, thanks for the response! It really did answer my question. This install is single-story commercial with a drop ceiling. Even though you said not to do something that everyone else does, the rest of the low voltage cable used in the install looks to be CMR. I'm fairly certain that means not plenum/fire rated, so I guess the CL2 will be okay as-is, at least for low voltage. I may just surround the hole with some fire caulking however for peace of mind, it's relatively cheap. May 1, 2019 at 4:56

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