Plenum Cable

A plenum space is an area of a building that circulates air for heating and cooling systems. These spaces can either be for the heated or cooled air or for the return flow. Dropped ceilings and raised floors also count as plenums if they facilitate the air circulation. Plenum cable refers to any cable that has been rated for use in plenum spaces.

Because plenum spaces have moving air in them, fire and smoke can move throughout a building at an accelerated rate once they reach them. The most important aspects a cable must have before being rated for plenum spaces deal with resistances. Plenum cables must resist flame and have low smoke emissions when they do come in contact with flame. Any fumes emitted must be non-toxic. 

A plenum rated cable could possibly be used in other areas depending on what type of cable it is. Certain types of plenum cable, like plenum fire alarm cable, will have even further restrictions on their uses. However, the restrictions placed on plenum rated cable make for a more expensive cable that might not be conducive for use in a non-plenum area. Therefore, most plenum cable will only ever be used in a plenum space, which limits the uses available for plenum cable.

Polyvinylchloride (PVC), Polytetrafluoroethylene (PTFE) and Fluorinated Ethylene Polymer FEP) are often used as the coating on the jacket that gives a cable its plenum rating. PVC is a thermoplastic polymer that is used often in other cable jackets and insulation.  During a fire, PVC releases a gas that provides its retardancy. The gas, HCI, can be toxic, but only under certain circumstances where the air is too hot to breathe. 

PTFE is often used as a coating on cookware that gives it a nonstick surface. This surface is achieved because PTFE is very nonreactive, and it is for this same reason that PFTE is used on plenum cables. FEP is like PTFE, only it is easier to make. It has the same nonreactive quality, which makes it resist flame.