What is a plenum air space

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bison

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Is an open joist and deck ceiling in a retail store considered a plenum ceiling. example; an exposed ceiling of a Walmart or Home Depot with roof top RTU's, no duct work, just supply and returns on the ceiling side of the roof top units.
I would appreciate any information on this subject, Thanks
 
Re: What is a plenum air space

Is there a space between a flat surface above the joist and a flat surface below the joist, thus forming a compartment or chamber, and is the air conditioning system pushing air through that space? If so, then yes it is a plenum.
 
Re: What is a plenum air space

An open ceiling in a retail store would not be a plenum area. If this was the case all the merchandise would need to be rated to be installed in environmental air ducts.
 
Re: What is a plenum air space

charlie b, The retail space is about 180,000 sq. ft. of open space, no suspended ceiling, it is wide open from concrete floor to metal roof deck.
so from my understanding, this ceiling space would not require plenum cabling. correct?
 
Re: What is a plenum air space

I intentionally picked the wording of my question out of the NEC Article 100 definition of ?plenum.? If there is no compartment or chamber, there is no plenum.
 
Re: What is a plenum air space

Sheet metal ductwork is a plenum for instance.

A room is not a plenum.

Add a dropped ceiling and the space above the ceiling may or may not be "Other Space Used for Environmental Air" but is never a plenum.


300.22(C) Other Space Used for Environmental Air. This section applies to space used for environmental air-handling purposes other than ducts and plenums as specified in 300.22(A) and (B). It does not include habitable rooms or areas of buildings, the prime purpose of which is not air handling.


FPN: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.
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Re: What is a plenum air space

Pop a ceiling tile and take a look. If you can see wood it's not an "other space for enviromental air. If the space is nothing but drywall, steel, and /or monokote it could be a plenum. Look at the return air grills. If they are not ducted then it's a plenum.
 
Re: What is a plenum air space

Larry I am confused with your post.

Air handling or not, the space above a suspended ceiling is not a plenum as far as I understand it.

[ September 20, 2004, 06:53 PM: Message edited by: iwire ]
 
Re: What is a plenum air space

Bob
My post was confusing. Please substitute the words "other space for enviromental air" in place of the word plenum.
FOr years and even today, people still call that space a "plenum". Old habits, especially bad ones die hard :D
 
Re: What is a plenum air space

What ever you call it an acoustical tile ceiling used as an air return needs plenum rated wiring and light fixtures
 
Re: What is a plenum air space

Originally posted by gmreynol:
What ever you call it an acoustical tile ceiling used as an air return needs plenum rated wiring and light fixtures
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All the light fixtures or other equipment need is a metal enclosure. Non-metallic equipment needs to be listed for the purpose.

300.22(C)(2) Equipment. Electrical equipment with a metal enclosure, or with a nonmetallic enclosure listed for the use and having adequate fire-resistant and low-smoke-producing characteristics, and associated wiring material suitable for the ambient temperature shall be permitted to be installed in such other space unless prohibited elsewhere in this Code.
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Re: What is a plenum air space

We replaced 250 metal can lights installed in new retail store because they were not plenum rated.
 
Re: What is a plenum air space

Posted by iwire:

Add a dropped ceiling and the space above the ceiling may or may not be "Other Space Used for Environmental Air" but is never a plenum
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I never knew this, but you are right. The handbook makes this very clear in 300.22. Still, the definition in article 100 seems to indicate such a space would be a plenum!!

Steve
 
Re: What is a plenum air space

Originally posted by sandsnow: Pop a ceiling tile and take a look.
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This has been an interesting discussion, but I would like to return to the original point. I think in the specific case described in the original post, there is no ceiling tile to pop. If you were to stand on the roof and drill a hole (e.g., to install a satellite dish), and looked into the hole, you would see the floor. No suspended ceiling exists. Therefore, no ?compartment? or ?chamber? exists. Therefore, no plenum exists. Put it another way: If you can stand on the floor and see the wire (OK, you might need binoculars), then the wire does not need to be plenum rated.
 
Re: What is a plenum air space

Originally posted by gmreynol: We replaced 250 metal can lights installed in new retail store because they were not plenum rated.
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Were they installed in a suspended ceiling? If so, that would be a different case then the one being described here.
 
Re: What is a plenum air space

gmreynol,
We replaced 250 metal can lights installed in new retail store because they were not plenum rated.
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If the can lights had a metal enclosure, and if the space they were installed in was "other space used for enviromental air", then the replacement was not required by the NEC. See 300.22(B)(2).
Don
 
Re: What is a plenum air space

Originally posted by charlie b:
This has been an interesting discussion, but I would like to return to the original point. I think in the specific case described in the original post, there is no ceiling tile to pop.
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I agree, I was responsible for the drift of the topic into areas that have ceilings.

I thought it was fairly clear that an open habitable space was not a plenum and that this would be good time to point out the space above a dropped ceiling whether used for air handling or not is never a plenum. :)

I find this to be a very misunderstood area of the NEC.

Bob

[ September 21, 2004, 03:28 PM: Message edited by: iwire ]
 
Re: What is a plenum air space

Sorry for the drift, but we did have to replace the 250 cans, fortunately the store furnished the cans. Not only did they have to buy new cans, that were built like nothing I've ever seen, they paid us to tear them all out and install the new ones. I heard a rumor that this wasn't the first time that this had happened to them. They save more money getting caught every once in a while than purchasing the so called expensive "plenum or environmental air..." rated cans.
 
Re: What is a plenum air space

gmreynol,
They save more money getting caught every once in a while than purchasing the so called expensive "plenum or environmental air..." rated cans.
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Plenum rated light fixtures are not required by the NEC for installations in a ceiling that is used for return air. They are not getting "caught", they are being forced to make an change that is not required by the NEC. If they would challenge this in court, it is very likely that the inspection authority would be required to reimburse them for these costs.
Don
 
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