Is this a Plenum?

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encoreman

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I have been asked to determine if certain areas are plenums. It is very critical since the type of cable we need to run is not available in plenum rated and is very difficult to put in conduit.

In this particular case, there is a room on the second floor of a building. In this room is an air handling unit. The discharge exits on one side of the unit and the return is on the opposite side. There is no ducting on the air handling equipment.

So, is this a plenum?

Can we run regular cable in this room?

Thanks in advance!

Jack
 
encoreman said:
I have been asked to determine if certain areas are plenums. It is very critical since the type of cable we need to run is not available in plenum rated and is very difficult to put in conduit.

In this particular case, there is a room on the second floor of a building. In this room is an air handling unit. The discharge exits on one side of the unit and the return is on the opposite side. There is no ducting on the air handling equipment.

So, is this a plenum?

Can we run regular cable in this room?

Thanks in advance!

Jack
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In my opinion, no otherwise anywhere there is a cold air return there is a plenum. Can you imagine the entire interior of my house being a plenum. That being said I would check with the ahj cause no telling what they will say.
 
Great example. I should have thought of that myself. I was reading in the nec Article 100 - "Plenum. A compartment or chamber to which one or more air ducts are connected and that forms part of the air distribution system."

So, in this case there is no "air distribution system".

Thanks for your quick reply and insight!

Jack
 
Although most people would call this a plenum, I believe calling this an "other space used for enviromental air" would be more correct. Wiring methods would have to be per 300.22(C).

In the NEC, 300.22(B) covers plenums. But per the NEC a plenum doesn't include air spaces above ceilings that most of us refer to as plenum spaces, and it also doesn't include an air handling room.
 
steve66
Although most people would call this a plenum, I believe calling this an "other space used for enviromental air" would be more correct. Wiring methods would have to be per 300.22(C).
In the NEC, 300.22(B) covers plenums. But per the NEC a plenum doesn't include air spaces above ceilings that most of us refer to as plenum spaces, and it also doesn't include an air handling room.
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Respectfully, IMHO, air handler rooms that are not ducted and use the room as part of the air distribution system is in line with the definition of Plenum in Article 100.
 
ron said:
Respectfully, IMHO, air handler rooms that are not ducted and use the room as part of the air distribution system is in line with the definition of Plenum in Article 100.
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Ron how is it different then a return grill anywhere in the building. The entire building is a plenum???
 
ron said:
Respectfully, IMHO, air handler rooms that are not ducted and use the room as part of the air distribution system is in line with the definition of Plenum in Article 100.
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Ron:

OK, I give. After looking at the definition, you're right about this being a plenum.

But I think I was still half right in that it can still be wired per 300.22(C). (Not that you ever said otherwise.)

300.22(B) refers to "ducts or plenums specifically fabricated to transport enviromental air".

It doesn't fit that, so we go to 300.22(C), which basically refers to all other air handling spaces.

So its a plenum space that can be treated as an "other space used for enviromental air", and wired per 300.22(C).

So the wiring still needs to be plenum rated, or in conduit.

Steve
 
300.22 (C)
(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.
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If the prime pursose of the room or space is air handling it is a plenum. In general wiring is not allowed to be installed in a plenum.

part of 300.22 (B)
Equipment and devices shall be permitted within such ducts or plenum chambers only if necessary for their direct action upon, or sensing of, the contained air
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(C) makes these other spaces that are not primarily for air handling - not a plenum.
 
I appreciate everyone's input. It gave me some good insight into the code and issues around plenums. The 200.22(C) was especially helpful.

Initially, I didn't read the code carefully enough. Article 100 "Plenum. A compartment or chamber to which one or more air ducts are connected and that forms part of the air distribution system."

300.22(C) ..."This section shall not apply to habitable rooms or areas of buildings, the prime purpose of which is not air handling."

The air handling unit in the space is for that space only. It is NOT part of an "air distribution system". It is habitable and the prime purpose is not air handling.
 
encoreman said:
I appreciate everyone's input. It gave me some good insight into the code and issues around plenums. The 200.22(C) was especially helpful.

Initially, I didn't read the code carefully enough. Article 100 "Plenum. A compartment or chamber to which one or more air ducts are connected and that forms part of the air distribution system."

300.22(C) ..."This section shall not apply to habitable rooms or areas of buildings, the prime purpose of which is not air handling."

The air handling unit in the space is for that space only. It is NOT part of an "air distribution system". It is habitable and the prime purpose is not air handling.
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I agree after reading your reply. For some reason, from your original question, I was picturing a large air handler that served a large portion of the building, located in a mechanical room. Somthing that had a common return flowing throguh that room.
 
kwired said:
300.22 (C)


If the prime pursose of the room or space is air handling it is a plenum. In general wiring is not allowed to be installed in a plenum.

part of 300.22 (B)


(C) makes these other spaces that are not primarily for air handling - not a plenum.
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It's a minor point, and maybe not entirely important. (And one I didn't understand until I read Ron's comment, and read the code again).

But a space can be a plenum, and still fall under 300.22(C).

If you read (C), it says it excludes plenums covered in (A) and (B). But (A) and (B) don't include ALL plenums. Just some.

So an example would be the return air space above a suspended ceiling. It's a plenum space. But (C) covers the wiring in this space, because its not a plenum covered in (A) or (B).

Steve
 
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