Residential Return Air

[jhawkbb]

We are wiring a new house and this thing has return air all over the place. The problem spot is in the basement. There is an island in the kitchen directly above a return air bay. I know wires can run across return air but how about diagonally up and through the floor? And what is the thought of recessed cans in return air (juno IC22W)? Metal boxes are accepted, so is a recessed can ok because it is all metal? Again due to duct work and return air being all over the ceiling in the basement we pretty much have to put them in return air unless we can talk the contractor into surface mounted fixtures to be mounted on round boxes that will fit under the ducts.

 

[kwired]

Strict reading of the requirements means NM cable can only pass perpendicular across the environmental air space.

Used to have an inspector that would count cables passing through on each side of a panned off floor joist bay, if there was same number and type of cables on each side he assumed they passed directly through. If not same he assumed one turned and went elsewhere in the environmental air space. Reality of this approach was that in some cases that he rejected there was still less NM cable exposed inside the environmental air space. NEC was not really all that clear (and still isn't this would have been about time 1993 NEC applied) as to whether it meant what he was interpreting - they must pass straight through and can not turn inside the environmental air space.

But you do have other options - use a wiring method that is suitable for use in environmental air space like AC or MC cable or any metal raceway.

Spaces above suspended ceilings that are used to handle environmental air have same requirement and the light cans are acceptable there, as well as AC/MC and metal raceways.

 

[wwhitney]

I know wires can run across return air but how about diagonally up and through the floor?

The language in the NEC 300.22(C) exception is

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.

Diagonally up and through the floor can still be perpendicular to the "long dimension of such spaces". Basically, the wire has to stay in a single cross section of the joist bay, be it crossing from side to side, or top to bottom, or diagonally.

Cheers, Wayne

 

[mopowr steve]

I'm not sure if you'll get dinged for the cans in the return air spaces for reasons of reducing the cross section of return air space for required cfm.

In critical areas like this with cans the HVAC guys and myself do a little dance to make things work out.

 

[Dennis Alwon]

Just sleeve the nm cable in metal flex.