Final answer:
Non-plenum rated cables can be used in a plenum if enclosed in a fire-rated duct or conduit. Plenum spaces require higher safety standards due to their role in air circulation.
Step-by-step explanation:
Cables that are not plenum rated can be used in a plenum when they are enclosed in a duct or conduit that has the proper fire-rating. Plenum spaces are areas of a building that facilitate air circulation for heating and air conditioning systems, and they usually have higher fire safety requirements because they can spread flames and smoke quickly throughout a building. To comply with building codes and regulations, cabling used in these areas must be plenum-rated or otherwise protected to prevent the spread of fire and toxic fumes in the event of a fire.