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). Cable trays are a support system for electrical cables, power, signal, and communication and optical fiber cables. However, not all installations require cable trays, and it's. NEC Article 392 governs cable tray installations, covering tray types, fill limits, cable types permitted, and ampacity adjustments. That's why knowing how to avoid damaging cables during this process is so important. The National Electrical Code (NEC).