All questions and answers are based on the 2017 NEC.
Q. What is the NEC rule regarding the continuity of cable tray systems and their accessibility?
A. Cable trays must be installed as a complete system, except mechanically discontinuous segments between cable tray runs, or between cable tray runs and equipment as permitted. The system must provide for the support of the cables and raceways in accordance with their corresponding Articles [Sec. 392.18] (Figure).
A bonding jumper, sized in accordance with Sec. 250.102 and installed in accordance with Sec. 250.96, must bond the sections of metal cable tray, or the cable tray and the raceway or equipment.
Each run of cable tray must be completed before the installation of cables or conductors [Sec. 392.18(B)].
Cable trays can extend through partitions and walls, or vertically through platforms and floors if the installation is made in accordance with the firestopping requirements of Sec. 300.21 [Sec. 392.18(D)].
Cable trays must be exposed and accessible, except as permitted by Sec. 392.18(D) [Sec. 392.18(E)].
Sufficient space must be provided and maintained about cable trays to permit adequate access for installing and maintaining the cables [Sec. 392.18(F)].
Q. What does the Code require for overcurrent protection of flexible cords, flexible cables, and fixture wires?
A. Flexible cord and flexible cable must be protected by an overcurrent protection device in accordance with its ampacity as specified in Table 400.5(A)(1) or Table 400.5(A)(2). Fixture wires must be protected against overcurrent in accordance with their ampacity as specified in Table 402.5. Supplementary overcurrent protection, as discussed in Sec. 240.10, can provide this protection [Sec. 240.5(A)].
Branch-circuit overcurrent protection must be provided for cords connected to listed appliances or luminaires. If flexible cord is used with a specific listed appliance or luminaire, the conductors are considered protected against overcurrent when used within the appliance or luminaire listing requirements of [Sec. 240.5(B)(1)]. Note: The NEC only applies to premises wiring, not to the supply cords of listed appliances and luminaires.
The branch circuit overcurrent protection device can be used to protect fixture wires when they are tapped to the following circuits [Sec. 240.5(B)(2)]:
(1) 20A – 18 AWG, up to 50 ft of run length
(2) 20A – 16 AWG, up to 100 ft of run length
(3) 20A – 14 AWG and larger
(4) 30A – 14 AWG and larger
(5) 40A – 12 AWG and larger
(6) 50A – 12 AWG and larger
Flexible cord used in listed extension cord sets is considered protected against overcurrent when used within the extension cord’s listing requirements 240.5(B)(3).
Q. What are the Code permitted uses of a cable tray?
A. Cable trays can be used as a support system for service, feeder, or branch-circuit conductors, as well as communications circuits, control circuits, and signaling circuits [Sec. 392.10]. Cable tray installations aren’t limited to industrial establishments. If exposed to the direct rays of the sun, insulated conductors and jacketed cables must be identified as being sunlight resistant. The manufacturer must identify cable trays and associated fittings for their intended use.
Cable trays used to support service-entrance conductors must contain only service-entrance conductors unless a solid fixed barrier separates the service-entrance conductors from other conductors [Sec. 230.44].
These materials are provided to us by Mike Holt Enterprises in Leesburg, Fla. To view Code training materials offered by this company, visit www.mikeholt.com/code.
