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). This is a description of how to select, install, and support these metal or plastic frames, on which electrical wires are installed. They can be rated for outdoor, indoor, for corrosive areas, for hazardous. 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. In my opinion the safety installation of cables [armored or not] it is running in metal conduits provided with approved accessories as glands or else. However according to IEC 60079-14 in certain location you may use armored cables. Hi, Does IEC. Tray cables are high-quality cables that have been tested rigorously and generally boast armor over individual conductors for superior insulation and a robust jacket that can withstand heavy abrasion.