I'm running cable for a motion sensor for our alarm system. I want to put it in the corner of the room and run the cable down inside the wall cavity, then through the right-side stud and down to a hole to the basement.

However, at the bottom of that wall (on the other side) is a cold air return from the adjoining room, and I know I can't run the cable in this space as long as it's part of the cold air return.

If I put a horizontal 2x4 above the cold air return and seal it with fire caulk, would that allow me to run the cable through the part of the wall I have now separated from the cold air return (safely and compliant with NEC)?

You can see the cold air return here; the 2x4 blocking would go above this opening, and the cable would be above that. Cold air return in wall

  • Will this cable carry line voltage or low voltage?
    – bib
    May 26 '16 at 10:30
  • Low voltage - 12 VDC over 22ga 4-conductor cable.
    – dabigjhall
    May 26 '16 at 11:20
  • If you use plenum rated cable it can be run in a air return but the cost are quite a bit higher for the wire. What about a piece of conduit? Since it is a open frame duct the 2X4 should work you have wires on the other side of those studs.
    – Ed Beal
    May 26 '16 at 13:41

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