Plenum cable is cable that is laid in the plenum spaces of buildings. The plenum is the space that can facilitate air circulation for heating and air conditioning systems, by providing pathways for either heated/conditioned or return airflows. Space between the structural ceiling and the dropped ceiling or under a raised floor is typically considered plenum; however, some drop ceiling designs create a tight seal that does not allow for airflow and therefore may not be considered a plenum air-handling space. It is imperative that you research your State and Local Building Codes before Installation as to what constitutes a Plenum space and what can, and cannot be placed there. Even non-Plenum Drop ceilings as defined herein may be considered Plenum Spaces according to your Local Code. The plenum space may be used to house the communication cables for computer and telephone network only if the Codes are followed to the Letter of the Law.