By definition, the plenum space (where plenum rated cable is used) usually includes the space above a drop or
false ceiling and below a
structural ceiling or below a raised floor, depending upon where
HVAC duct is located.
Given this definition, some inspectors will say that
plenum rated cable is requires ANYWHERE within the above-named spaces. Other inspectors insist that
installers may use
PVC cable as long as they are not entering an area of
moving air.
Plenum Cable is often manufactured with
Teflon, while the non-plenum varieties are most often found to use
PVC and other toxic components. The
composition of the plenum rated cable allows it to produce less smoke than non-plenum cable when subjected to heat and fire.
The plenum rating requirement is intended to reduce the potential smoke
inhalation risk and toxicity to building
occupants during a
fire situation.