While the choice largely depends on the environment and volume of cabling, the most commonly used systems fall into three main categories: cable trays, cable trunking, and conduits. Cable Load and Thermal Management 2. 2. The NEC defines cable trays as “a unit or assembly of units or sections and associated fittings forming a rigid structural system used to securely fasten or support cables and raceways. ” That is, cable trays are infrastructure used to support and convey electrical cables - which are not enclosed. To that end this Bulletin is intended to discuss the types of cables most frequently used in cable trays and the wiring methods permitted in cable trays under the National Electric Code (NEC) NFPA 70. In general, tray rated cables are quality products that have been tested to withstand the rigors. The cable trays are open, and this helps wires to cool because of the circulation of air around them. Conduits are enclosed pipes that trap the heat. When the electricity travels through a wire, this wire becomes hot.
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