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). (1) Only the following may be installed in cable tray systems: (a) Mineral-insulated metal-sheathed cable (Type MI); (b) Armored cable (Type AC); (c) Metal-clad cable (Type MC); (d) Power-limited tray cable (Type PLTC); (e) Nonmetallic-sheathed cable (Type NM or NMC); (f) Shielded. Only approved tray-rated cables should be installed. Grounding and bonding are mandatory for metallic trays. Tray fill limits must be calculated properly. Mesh trays reduce installation time while. Cable Trays have been permitted in the hazardous (classified) locations in the National Electrical Code for Class I (flammable vapor and gases) since the 1978 NEC and have been used extensively in chemical plants, refineries, and other types of facilities. This is a description of how to select, install, and support these metal or plastic frames, on which electrical wires are installed.
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