To safeguard of persons and property from electrical hazards, when installing cable in a Plenum ceiling you want to be sure that you use Plenum cable.
What is a Plenum Ceiling?
According to Article 100 of the Nec, "Plenum" is "a compartment or chamber to which one or more air ducts are connected and that forms part of the air distribution system".
Why is plenum Cable different?
Plenum cable is coated with a flame-retardant material that reduces the amount of toxic fumes and smoke when burned. Toxic fumes and smoke can become a dangerous factor in plenum ceiling for the simple reason that a Plenum ceiling design can allow for these toxic fumes and smoke to travel through air ducts to the whole building during a fire.
The NEC quotes made here is for general information purposes only and cannot be guaranteed typing or interpretation accuracy. It's recommended that a check with the local Fire Marshall and or Building inspector in your area to advises you on the code for your community.