Glossary  >  Plenum



Definition of Plenum: The plenum refers to an enclosed space or chamber above the drop-down ceiling or under raised floors used to provide air circulation, heating, ventilation, and HVAC systems within a building.

Plenum is also used in networking to refer to cables rated for use within plenums—thus, plenum-rated cables. Plenum-rated cables are also known as Communications Multi-purpose Plenums (CMP). They have a higher flame rating and pose a lower risk of spreading fire or introducing toxic smoke within the plenum and, by extension, a building's airflow.

When installing a cell phone signal booster, use plenum-rated cables to meet the code and safety standards. The best way to ensure this is to have your signal booster professionally installed by a reputable company.

The most commonly non-plenum cables include communications multipurpose riser (CMR) and communications multipurpose cables (CM).

Type Fire Resistance Applications Jacket Material Toxic Fumes Cost
CMP High fire resistance Rated for use in plenum airspaces Fire-retardant PVC or FEP Jacket Produces low levels of toxic fumes Most expensive
CMR Moderate fire resistance Used in vertical applications and risers Standard PVC jacket Produces higher levels of toxic fumes Less expensive than CMP
CM Minimal fire resistance Fit for non-fire code rated applications Standard PVC jacket Produces higher levels of toxic fumes Least expensive

Example of Plenum in a sentence

"Building codes require that only plenum rated cables are used in plenum spaces."

Related Terms for Plenum