Plenum or not?

[linksolo]

I am looking at a building structure that is open from the floor to the roof structure (no drop ceiling). The air handling units are mounted on the roof top itself and are ducted through the roof into the space below. Both the distribution air and the return air are ducted down to 10-15' AFF. It is essentially built like a warehouse structure but does have drop ceilings in some areas. I am trying to find out if plenum rated cable is required in this environment. All cables will be installed at 25' AFF in the roof structure. We submitted non-plenum rated cable and it was approved and it was also detailed in the estimate.

 

[cowboyjwc]

If everything is ducted, then it's not a plenum.

 

[linksolo]

Even if the duct is placed in the open areas right? I attached a basic drawing to make sure we are on the same page.

 

[GoldDigger]

Even if the duct is placed in the open areas right? I attached a basic drawing to make sure we are on the same page.

Yes.
And if there had been a suspended ceiling and the air duct terminated at gratings in the suspended ceiling, the answer would still be yes.
But if a duct (either supply air or return air) ended above the suspended ceiling and the air flowed down (or up) through gratings in the suspended ceiling, then the space above the ceiling would still not be a plenum under NEC, but it would be "other environmental air space" and some restrictions would apply to wiring placed above the ceiling.

 

[Smart $]

Even if the duct is placed in the open areas right? I attached a basic drawing to make sure we are on the same page.

I'm in agreement with cowboy John.

The plenum rules do not apply to habitable areas for which the prime purpose is not air handling [300.22(C)]. The ducts themselves separate the habitable area from spaces which the prime purpose is air handling.

 

[linksolo]

Thanks for your clarification guys. I appreciate it.