Instrumentation, signal, and telecommunications cabling should be separated from power cabling. This can be accomplished by a separate cable tray system or by a divider within a. NEC 392 recognizes several cable tray types, each with different structural properties and ventilation characteristics that affect fill rules and ampacity. Ladder tray consists of two side rails connected by rungs, similar to a ladder laid flat. It provides the best ventilation because air flows. NEC Article 392 explains cable trays, their components, appropriate wiring methods for cable trays, and instances where they are and are not permitted for use. It also focuses on construction and installation practices for cable trays.