Article 392 Cable Trays

Cable tray can be used as a support system for branch circuits, service conductors, feeders, services, communication circuits, control circuits, and signaling circuits. It is not limited to industrial locations. If it is exposed to direct sunlight then jacketed cables or insulated conductors that are sunlight resistant must be used.

(A) Wiring Methods. Refer to the noted article or section for the conditions of use of the following:

(B) In Industrial Establishments. Wiring methods of 392.3(A) can be used in accordance with their respective article's requirements. Where only qualified maintenance personnel are available, certain cables are permitted in ladder, ventilated trough, and ventilated channel-type cable trays. Single-conductor cable must be 1/0 AWG or larger and be permitted to be used in cable tray. If the cable is sized 1/0 AWG through 4/0 AWG, it must be installed in ladder-type cable tray with a maximum rung spacing of 9 in. or in ventilated trough cable tray. Welding cable can be installed in accordance with Article 630, Part IV. Equipment grounding single conductors can be insulated, covered, or bare 4 AWG or larger. Multiconductor cable type MV can also be installed as noted above.

(C) Equipment Grounding Conductors

(D) Hazardous (Classified) Locations

(E) Nonmetallic Cable Tray

Cable trays cannot be used where they are exposed to severe physical injury, in hoistways, and in environmental air-handling spaces. An exception is made in the latter case where used to support a wiring method noted in Section 300.22.

Cable trays must have proper strength and rigidity, smooth edges, be protected against corrosion, have side rails, and contain the proper fittings. Flame-retardant material must be used for nonmetallic cable tray.

The cable tray system must be installed completely as a system before the cables are installed, have the proper supports, and have covers where required. Multiconductor cables can be installed in the same tray if 600 V or less. Cables over 600 V cannot be installed with cables under 600 V, with two exceptions. The cable trays must be exposed and accessible and have room around them for adequate access. They can go through partitions, walls, and floors if installed in accordance with Section 300.21 (proper and approved firestopping methods used). Incidental support from cable tray is permitted where approved and designed to support the load. Additional requirements are noted.

Proper grounding must be attained in compliance with Article 250.96. The entire system must be grounded. Minimum size steel and aluminum trays are indicated in Table 392.7(B) of the NEC®.

1. Splices are permitted if approved methods are used, they are accessible, and are not over the side rails.
2. Cables must be fastened in sloping or vertical runs.
3. If the cable is installed in a bushed conduit and tubing for protection or support, a box is not required.
4. If installed in parallel, the conductors must be grouped with one conductor per phase in each group. Single conductors must be bound in circuit groups.
5. Single conductors.

Refer to this section in the Code and Table 392.9.

Refer to this section in the Code and Table 392.10(A).

(A) Multiconductor Cables. Multiconductor cables, rated 2000 V or less, installed as per Section 392.9 are to follow ampacities in Tables 310.16 and 310.18. The derating factors of Section 310.15(B)(2)(a) apply only to multiconductor cables of three or more current carrying conductors in cable, not in cable tray. If the tray is covered for more than 6 ft. with a solid unventilated cover, the ampacities allowed are 95% of those shown in the tables. An additional exception is allowed for a single layer in uncovered trays.

(B) Single Conductor Cables. The derating factors of Section 310.15(B)(2)(a) don't apply to cables in cable tray. Single conductor or single conductors cabled together, rated 2000 V or less, properly installed in accordance with the Code, are to use ampacities as follows:

(1) Cables 600 kcmil and larger in uncovered trays use not more than 75% of the ampacities in Tables 310.17 and 310.19. If the tray is covered for more than 6 ft. with unventilated covers, use a maximum 70% of the ampacities in the tables.

[*] See Section 240.4(D).

(2) Cables 1/0 AWG through 500 kcmil in uncovered trays use not more than 65% of the ampacities in Tables 310.17 and 310.19. If the tray is covered for more than 6 ft. with unventilated covers, use a maximum 60% of the ampacities in the tables.

(3) If single conductor cables are placed in a single layer with at least one cable diameter separation, the tray is uncovered and the cable is 1/0 AWG or larger, the ampacities in Tables 310.17 and 310.19 may be used. There is one exception.

(4) Special allowance when installed in uncovered tray with a triangular configuration.