Due to their exposure to the open air because of the cable trays, the wires contained within need a very durable outer covering. The regulations dictate that the cables must either be Type TC (also known as Tray Rated) or must be metal-armored (Type MC). Can any cable be used in a tray? The short answer is no. Cable trays are a support system for electrical cables, power, signal, and communication and optical fiber cables. NEC section 300-8 does not permit. According to the 2005 National Electrical Code® (NEC), a cable tray system is “ unit or assembly of units or sections and associated fittings forming a structural system used to securely fasten or support cables and raceways. ” Cable trays support cable across open spans in the same manner that. Cable tray systems provide a safe, organized, and flexible method for supporting insulated conductors and cables in commercial and industrial electrical installations.