When the cable tray is installed outdoors, the cable tray should be equipped with a protective cover at its upper layer or each layer. It instructs us on how to construct them, where to locate them, and how to stuff them with wires without using too much. These regulations ensure that the metal or plastic frames that contain the wires are robust enough to ensure. 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. 6 (requirements for cable tray installations). These essential components: Example: Stainless steel covers meet NEC 392. 10 (B) corrosion resistance.