Plenums

[stonecutter]

In a 3 and 4 story town house style dwellings with attached 2 car garage, I have contractors who are being required to install a fire sprinkler system. The contractor has run the the sprinkler pipe in the garages to drop 4 heads in each garage. The original garage ceiling is 12' in height. The builder did not board the garage ceiling at 12'. The panel board is in the garage and all wiring is properly supported throughout the ceiling and walls.
So, the sprinkler heads were required to be dropped 3 feet per fire marshal instructions. So, they dropped the heads and installed a drywall ceiling at 9 feet to meet the heads. The sprinkler system is a wet system, and in our region, the likelyhood of the sprinkler pipe freezing is very high, so the building contractor has the mechanical contractor supply heat from the furnace to the space in between the original 12 foot ceiling and the new 9 foot ceiling. There is no return vent for this space, only a supply air. Is the space above the 9 foot ceiling considered a space being used for environmental air and should the wiring, which is NMC throughout, be changed to meet the requirements of NEC art. 300.22 (2014)?
Would like to hear your opinions on this.
Thank you

 

[publicgood]

Tough one. I’d say yes since the environmental air definition uses OR. With the goal of non-plenum wiring methods having potential to produce smoke.
—
Informational Note No. 1:  The space over a hung ceiling used for environmental air-handling purposes is an example of the type of other space to which this section applies.
Informational Note No. 2:  The phrase “Other Spaces Used for Environmental Air (Plenum)” as used in this section correlates with the use of the term “plenum” in NFPA 90A-2012, Standard for the Installation of Air-Conditioning and Ventilating Systems, and other mechanical codes where the plenum is used for return air purposes, as well as some other air-handling spaces.

Plenum. A compartment or chamber to which one or more air ducts are connected and that forms part of the air distribution system

Air Distribution System. A continuous passageway for the transmission of air that, in addition to air ducts, can include air connectors, air duct fittings, dampers, plenums, fans, and accessory air-handling equipment but that does not include conditioned spaces.

Environmental Air. Air that is supplied, returned, recirculated, or exhausted from spaces for the purpose of modifying the existing atmosphere within the building.

 

[hbiss]

No. The environmental air in an environmental air space is conditioned air that is recirculated throughout an occupied space using the space above the ceiling as a return duct. That's why it's important to limit the amount of smoke and combustion gasses that cables in that space can give off because it will be distributed throughout the occupied areas.

But in this case it's just a dead end. It's a heated space with no return. So I wouldn't call it an environmental air space.

-Hal

 

[GoldDigger]

No. The environmental air in an environmental air space is conditioned air that is recirculated throughout an occupied space using the space above the ceiling as a return duct. That's why it's important to limit the amount of smoke and combustion gasses that cables in that space can give off because it will be distributed throughout the occupied areas.

But in this case it's just a dead end. It's a heated space with no return. So I wouldn't call it an environmental air space.

-Hal

:thumbsup:

Plenum. A compartment or chamber to which one or more air ducts are connected and that forms part of the air distribution system

Air Distribution System. A continuous passageway for the transmission of air that, in addition to air ducts, can include air connectors, air duct fittings, dampers, plenums, fans, and accessory air-handling equipment but that does not include conditioned spaces.

I have to agree that it is not a plenum space by any definition, nor is it part of the air distribution system, as the area over a suspended ceiling that is used for air return would be. The clincher is that last part, that rules out simple conditioned spaces. It is not delivering air somewhere else, it is the destination. Even if there were a return duct in the above ceiling space, it would not IMHO be any thing but a simple conditioned space.