What is the purpose of a plenum in an air distribution system?

The purpose of a plenum in an air distribution system is primarily to connect air ducts and facilitate the distribution of conditioned air throughout a building. A plenum acts as a central distribution point where air can flow freely, either as a supply for heating and cooling or as a return path for air to be re-circulated. This function is essential for maintaining proper airflow and ensuring the efficiency of the HVAC system.

While the other options pertain to important aspects of electrical systems and environmental protection, they do not relate to the specific role of a plenum within air distribution. For instance, regulating electrical circuits, housing circuit breakers and fuses, or protecting wiring from moisture are functions that deal with electrical installations and safety rather than the air distribution mechanism. Therefore, the connection of air ducts through the plenum is what makes the function of a plenum vital in HVAC systems.