NM running through a plenum

Is there any “code” that allows a NM cable to run through a cold air return made up of two floor joists that are boxed in? The cable is more than 1-1/4" from the edge of the joist. I don’t have a picture as my battery died (a different electrical question :mad:)

Yes it is permitted as long as the cable only runs perpendicular to the studs.

This has confused me in the past. Are you saying this based on 300.22© and the way the return was built, not being specifically fabricated.

I’m guessing the exception in 300.22 © is what applies. This section shall not apply to the joist or stud spaces of dwelling units where the wiring passes through such spaces perpendicular to the long dimension of such spaces.

Yes, the NEC code reference would be 300.22©Ex. The NM cable can go through from one joist or stud to other but the cable cannot run parallel to the joist or stud.