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.