What are plenum-rated cables designed for?

Plenum-rated cables are specifically designed for installation in air-handling spaces, which are areas used for air circulation and where air ducts may be located. These spaces can be found in ceilings or under raised floors in commercial buildings where the HVAC systems operate. Because these cables are often in close contact with airflow, they must meet strict fire safety standards to minimize the release of toxic fumes and smoke in the event of a fire. The outer insulation of plenum-rated cables is made from materials that have lower flame spread and smoke generation characteristics, making them suitable for such environments.

The other options refer to different installation contexts that do not require the same level of fire safety considerations as plenum spaces. For instance, underground installations and exterior installations have different environmental exposures and safety requirements, while residential wiring is usually subject to local building codes that vary by jurisdiction but do not typically involve the same fire hazard risks associated with air-handling spaces. Therefore, the design and purpose of plenum-rated cables are focused on ensuring safety in environments where air circulation may be affected by the presence of combustible materials.