Under what condition can non-plenum rated cables be used in a plenum?

Using non-plenum rated cables in a plenum is permitted when they are installed in a plenum-rated raceway. This is important because plenum spaces are areas designed for air circulation in heating and air conditioning systems, which can pose a significant fire hazard if non-plenum rated cables are used. Plenum-rated cables are specifically designed with materials that have a lower flame spread and produce less smoke when they burn, making them safer for use in such environments.

By housing non-plenum rated cables in a plenum-rated raceway, the raceway provides a barrier that helps contain any potential fire hazards and limits the spread of smoke, thus adhering to safety codes and regulations. This approach allows for the use of non-plenum rated cables while still maintaining the safety and integrity required in plenum spaces, as the cable itself is not directly exposed to the plenum environment.