When it comes to managing and protecting cables in various environments, both cable trays and cable ducts serve as essential components. However, they are not interchangeable. Each system has unique characteristics that make it more suitable for specific applications. An air duct is a sealed conduit that forms the critical pathway of a building's Heating, Ventilation, and Air Conditioning (HVAC) system. Understanding the differences. Section 318-4 Uses Not Permitted states that “Cable tray systems shall not be used in environmental air spaces except as permitted in Section 300-22 to support wiring methods recognized for use in such spaces. NEC Article 392 recognizes these types: Ladder tray — Two side rails connected by rungs; best airflow, most common in industrial plants. Solid-bottom tray — Full solid floor; provides physical protection and containment. A bus duct (busway system) is a prefabricated power distribution system that uses solid copper or aluminum busbars enclosed in a protective housing. What Is a Cable Tray? A cable tray is a mechanical support system designed to hold and organize insulated electrical cables.