Plenum & Non Plenum Cable

Plenum and Non Plenum refer to two types of cable insulation. A plenum area is a duct, or simply the space above the drop ceiling, from which air is drawn back into the air circulation system. Cable in plenum areas must meet standards for low smoke generation in case of a fire. If in doubt, presume plenum, because the fire marshall could make you pull it all out if you are wrong. The cost premium for plenum rated Cat3 cable is very small, but due to a worldwide shortage of plastic manufacturing capacity for Cat5 plenum insulation, the premium for Cat5 plenum is about double non plenum.