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. NEC section 300-8 does not permit any tube, pipe, or equal for water, air gas, drainage, steam, or any service other than electrical in raceways or cable trays containing. Compared to ordinary power cables, armored cables can resist external impacts, pressure, abrasion, and rodent damage, making them widely used in underground tunnels, cable tray systems, chemical plants, mines, outdoor installations, and data communication networks. You should consider it as a series of instructions that make the buildings resistant to. maintain spacing or to keep cables in place when the tray is ect the minimum bend ra-dius for cables as they exit the bottom of the cable tray. A rung spacing of 6 to 9 inches (150 to 230 mm) is preferable when the cable tray cont d for instrumentation and control applications that require. Armored cables are used in applications where cables will be exposed to mechanical or environmental damage under normal operating conditions. These applications include power circuits in industrial plants, commercial buildings, processing plants and central and substation utility applications. However according to IEC 60079-14 in certain location you may use armored cables.