When is a drop ceiling considered a plenum?

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flownder

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Is the drop ceiling always considered a plenum, regardless of the drop ceiling purpose, i.e., CRAC air return? If this is the case, then any cable not plenum rated will not be allowed above the drop ceiling. Is there any situation where non plenum rated cable (SOOW or TC, tray cable) will be allow in the drop ceiling.

I have come across a situation where someone want to run a 3-phase, TC rated whip, from a PDU, over a wall via the drop ceiling and power equipment of the other side. The ceiling is not being used as an air return plenum. Can this be done? This site is in Las Vegas for those who know local code.

Thanks for your help.
 
Re: When is a drop ceiling considered a plenum?

Simple answer is that type TC can't be used like this anyway. See Article 336.

You could run it in EMT (but then just pull THHN conductors) or you could use MC.

-Hal
 
Re: When is a drop ceiling considered a plenum?

If the space above the drop ceiling is used for environmental air transfer, meaning the air above the drop is apart of the air return, then it is a plenum area and plenum rated cables shall be installed.
 
Re: When is a drop ceiling considered a plenum?

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

If the cavity is used for return air I think it's other space for environmental air 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.
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. It depends on the installation.

Charlie
 
Re: When is a drop ceiling considered a plenum?

i assume that the above ceiling is a plenum if part of a return path, supply for environmental air.

paul
 
Re: When is a drop ceiling considered a plenum?

Paul,
i assume that the above ceiling is a plenum if part of a return path, supply for environmental air.
Click to expand...
No. That would be "other space used for enviromental air", as Charlie pointed out.
Don
 
Re: When is a drop ceiling considered a plenum?

I agree with Don and Charlie. It seems the NEC definition of a plenum is different than what HVAC people use. I think our mechanical engineer would call it a plenum, but the NEC doesn't.

Steve
 
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