# JB's in plenum space



## NJELEC (Oct 19, 2010)

Not sure if this has been addressed before, but can anyone provide a code section that requires junction box's (1900 / 411's) to be plenum rated in a space that is used for air handling? 300.22(C) refers to "metal enclosures", 314 wasnt helpfull either. I have not been able to find a section that requires metal box's have to be vapor tight or plenum rated. I've used plenum box's in the past but never questioned what drove the requirement for them.


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## MechanicalDVR (Dec 29, 2007)

NJELEC said:


> Not sure if this has been addressed before, but can anyone provide a code section that requires junction box's (1900 / 411's) to be plenum rated in a space that is used for air handling? 300.22(C) refers to "metal enclosures", 314 wasnt helpfull either. I have not been able to find a section that requires metal box's have to be vapor tight or plenum rated. I've used plenum box's in the past but never questioned what drove the requirement for them.


 
Anything that is within the plenum space has tobe plenum rated.


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## NJELEC (Oct 19, 2010)

Agreed, but can you provide a code section that requires metal box's to be rated for air handling space?


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## raider1 (Jan 22, 2007)

What kind of air handling space are we talking about?

300.22(C)(3) deals with boxes installed in suspended ceiling spaces used for return air.

Chris


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## NJELEC (Oct 19, 2010)

typical 2X4 suspended ceiling. Raised floor below, wall cavities will provide return path to ceiling. area will be used for electronic production. I agree the extra steps are required to maintain a clean air supply, but I have not been able to assign a defined NEC section that requires metal box's to be "plenum rated" or "approved for air handling spaces". Could fall under the building code??


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## Dennis Alwon (May 9, 2009)

All you need are metal jb. Think of the jb's in suspended ceilings all over the world where the ceiling is a plenum. We typically use 4" sq. box. Even some plastic boxes can be plenum rated. I don't see the issue with metal enclosures.


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## don_resqcapt19 (Jul 18, 2010)

There are sealed boxes available and they are required by the Chicago code. The NEC does not require anything special in a 300.22(C) space.


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## NJELEC (Oct 19, 2010)

I've used the sealed type in the past. Engineer specified the plenum box right before we start the project. Curious if it was code driven, AHJ, or preference. Thanks for the feedback


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