ECN Forum Forums Code Related Discussion NEC & other Code issues Cold Air Returns

When installing NM cable in a dwelling unit, do the inspectors require metal wiring methods in CA returns?

Joe- the issue that seems to have come up is the wording "passing through" versus "terminating in" the CA. If it passes through the CA perpendicular to the long dimension I don't see a problem but when you start installing boxes it's debatable. I'm curious how this forum feels about it.

I think the code prohibits it. I also think that it is a silly prohibition. The IRC allows anything, other than gas piping, to be installed in a plenum. For example, I could run a 4" ABS lengthwise through a plenum, and that wouldn't matter. I can't do this with 14-2 NM cable, however.

The "passing through" language is meaningful.
When you install a box in a return plenum, the box becomes a return air register. It is just like the dumb idea of PCs "breathing" through the diskette drive.
They end up packed with dirt.
In a dwelling that dirt could be combustible.

BTW a Florida guy would ask why you are "returning" cold air? That is the supply side.

gfretwell,

What about the "hot" water heater?

We keep it outside.

Why does hot water need to be heated, anyway?

Hot water needs to be heated for cleaning dishes as in a restaurant. They are called booster heaters and are used to increase the temperature to a higher level to meet health department requirements,

How did we migrate to this from derating NM cable?

As luck would have it, there is a new pic in the Photo forum that illustrates this issue.