Keep in mind that although plenum rated wiring methods may be required, the space above a dropped ceiling is not really a plenum. It is at most "other environmental air" space.Is the space an open return (no return ducts or partial return ducts)? Many years ago I could just shine a flashlight through the ceiling return grill; if I saw no sheet metal above the grill, the above-ceiling space was a plenum. If I saw sheet metal, returns were fully ducted back to the air handler.
Then they started using what I called a "directing duct" (a 90 directing the air flow toward the air handler); so much for the flashlight. It became "up the ladder" and if there was even one return not fully ducted, the space was a plenum. I'm sure my use of "worst case" may have cost me some jobs, but it always kept me in the good graces of inspectors.
Exactly.Keep in mind that although plenum rated wiring methods may be required, the space above a dropped ceiling is not really a plenum. It is at most "other environmental air" space.
If it were actually s plenum the wiring restrictions would be much more restrictive (nothing but air related circuits, and even those strictly limited.)
We do this as well. In fact, we just run plenum rated no matter where it's going. Keeps everything simple.It is a tough question (for me).
NFPA 13 defines a concealed space differently than NFPA 70 (NEC), and according to 13, the space above a suspended ceiling is concealed space. Thus either requiring sprinkler coverage or no combustibles to be in that space.
Many AHJ's consider plenum wiring to be "non-combustible", although of course it is combustible and maybe just low smoke producing.
Because of this, I interpret the code to require plenum rated cabling above a suspended ceiling, because we generally do not put fire suppression heads above a suspended ceiling.
I will be running plenum rated also, it's just the fact I already have the riser rated (cmr) in the garage. (you would think a riser if I'm interpreting correctly would need plenum also)We do this as well. In fact, we just run plenum rated no matter where it's going. Keeps everything simple.