Plenum Definition

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	Question by Bruce Moss posted 16 Sep 2005
	Plenum Definition
I have a buiding with lab areas and within the ceilings the sealed air ducts. Is the area around the ducts considered "Plenum" area? Thanks
	Answer by Joseph Golan posted 16 Sep 2005
Dear Bruce, A plenum area is typically used for the return air of an air conditioning system. If your ducts are only a "supply" then you most likely have a return plenum environment which will require plenum rated cable. If you have separate supply and "return" ducts then the void above the dropped ceiling is not being used for a return air plenum. Another easy way to tell is if you have open grills or grill space around the lighting fixtures then is is most likely a return air plenum. Sonme locals require plenum rated cable for communication cabling even if it is not renning through a return air plenum space. Please check will your local inspector or the AHJ (Authority Having Jurisdiction for the final say. Sincerely, Joseph Golan, RCDD
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