Ethernet Plenum Cat5e Cable: Plenum cable is cable that is laid in the plenum spaces of commercial and residential buildings (dropped ceiling, raised floor). The plenum space is typically used to house the communication cables for computers and telephones. However, these plenum spaces can become fire hazards. Since plenum spaces hold a fresh stream of oxygen, if a fire hits a plenum space, the oxygen can feed and spread the fire through the entire plenum space throughout the structure. Plenum cable is coated with a fire-retardant coating so that in case of fire it does not give off toxic fumes as it burns. For this reason, plenum cable is used instead of regular cable to meet fire codes in place for laying communication cable in plenum spaces.