Plenum Spaces

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 Question by David Takanashi posted 24 Oct 2002
 Plenum Spaces
Hello,

I am inquiring about information reguarding plenum spaces. I am a small company and am having a hard time finding answers to when I am required to use plenum rated cable. I have asked many different people and the answers vary. I was under the impression that I was required to use it in office environment with drop celings but with further investigation I was under the impression that I would only need it if I was actually going through an air vented space. For instance if I had to go directly through a vent because there was no way around it. I was also told that if I asked the owner of the building or the building management then they should know if it has to be plenum cable. Also if the job requires plenum is it an industry standard to charge for the extra price or do you pick up the cost? Any information will be greatly appreiciated.

Thanks,

David
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 Answer by Dmitri Abaimov posted 28 Oct 2002
Dear David ,

The plenum is considered ANY space that let air move in it. Basically, if you have drop ceiling office, you need plenum with the only exception: if you have ducted air returns (returns, not feeds, it's important). The reason is really simple and logical: unless you have ducted returns, you do not control the way the air takes to escape the high pressure locations. Therefore, it will most likely move freely above the ceiling, bringing fresh oxygen to possible flames and spread fire really quick.
The owner may not know definition of plenum space, but he/she will definitely be able to tell how HVAC is designed in your space. This way you'd know if you need to use plenum cable.

Cabling industry is the same as all the others: if there is an extra cost involved, a customer ultimately pays for it. The cable is nearly three times more expensive, which will bring the cost of your cabling up, obviously. On the other hand, if they don't use plenum-rated (CMP) cable, the building will not conform to fire code, and the cabling will have to be replaced, which will cause greater financial damage.

Sincerely,
Dmitri Abaimov, RCDD
Dear David ,

The plenum is considered ANY space that let air move in it. Basically, if you have drop ceiling office, you need plenum with the only exception: if you have ducted air returns (returns, not feeds, it's important). The reason is really simple and logical: unless you have ducted returns, you do not control the way the air takes to escape the high pressure locations. Therefore, it will most likely move freely above the ceiling, bringing fresh oxygen to possible flames and spread fire really quick.
The owner may not know definition of plenum space, but he/she will definitely be able to tell how HVAC is designed in your space. This way you'd know if you need to use plenum cable.

Cabling industry is the same as all the others: if there is an extra cost involved, a customer ultimately pays for it. The cable is nearly three times more expensive, which will bring the cost of your cabling up, obviously. On the other hand, if they don't use plenum-rated (CMP) cable, the building will not conform to fire code, and the cabling will have to be replaced, which will cause greater financial damage.

Sincerely,
Dmitri Abaimov, RCDD

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