CABLE TRAYS

318-1. Scope. This article covers cable tray systems including ladders, troughs, channels, solid bottom trays, and other similar structures. 318-2. Definition. Cable Tray System. A unit or assembly of units or sections, and associated fittings, forming a rigid structural system used to support cables and raceways. 318-3. Uses Permitted. (a) Wiring Methods. The following shall be permitted to be installed in cable tray systems under the conditions described in their respective articles: (1) Mineral-insulated, metal-sheathed cable (Article 330); (2) electrical nonmetallic tubing (Article 331); (3) armored cable (Article 333); (4) metalclad cable (Article 334); (5) nonmetallic-sheathed cable (Article 336); (6) shielded, nonmetallic-sheathed cable (Article 337); (7) multiconductor service-entrance cable (Article 338); (8) multiconductor underground feeder and branch-circuit cable (Article 339); (9) power and control tray cable (Article 340); (10) power-limited tray cable (Sections 725-50, 725-51, and 725-53); (11) other factory-assembled, multiconductor control, signal, or power cables that are specifically approved for installation in cable trays; (12) intermediate metal conduit (Article 345); (13) rigid metal conduit (Article 346); (14) rigid nonmetallic conduit (Article 347); (15) electrical metallic tubing (Article 346): (14) rigid nonmetallic conduit (Article 347); (15) electrical metallic tubing (Article 348); (16) flexible metallic tubing (Article 349); (17) flexible metal conduit (Article 350); or (18) liquidtight flexible metal conduit and liquidtight flexible nonmetallic conduit (Article 351). (b) In Industrial Establishments. In industrial establishments only, where conditions of maintenance and supervision assure that only qualified persons will service the installed cable tray system, any of the cables in (1) and (2) below shall be permitted to be installed in ladder, ventilated trough, 4-inch (102-mm) ventilated channel cable trays, or 6-inch (152-mm) ventilated channel cable trays. (1) Single Conductor. Single conductor cable shall be No. 1/0 or larger and shall be of a type listed and marked on the surface for use in cable trays. Where Nos. 1/0 through 4/0 single conductor cables are installed in ladder cable tray, the maximum allowable rung spacing for the ladder cable tray shall be 9 inches (229 mm). Where exposed to direct rays of the sun, cables shall be identified as being sunlight-resistant. Exception No. 1: Welding cables as permitted in Article 630, Part E. Exception No. 2: Single conductors used as equipment grounding conductors shall be permitted to be No. 4 or larger. (2) Multiconductor. Multiconductor cables Type MV (Article 326) where exposed to direct rays of the sun shall be identified as being sunlight-resistant. ARTICLE 318 - CABLE TRAYS 70-199 (c) Equipment Grounding Conductors. Metal in cable trays, as defined in Table 318-7(b) (2), shall be permitted to be used as equipment grounding conductors in commercial and industrial establishments, only where continuous maintenance and supervision assure that qualified persons will service the installed cable tray system. (d) Hazardous (Classified) Locations. Cable trays in hazardous (classified) locations shall contain only the cable types permitted in Sections 501-4, 502-4, 503-3, and 504-20. (e) Nonmetallic Cable Tray. Nonmetallic cable tray shall be permitted in corrosive areas and in areas requiring voltage isolation. (FPN): It is not the intent of this article to limit the use of cable trays to industrial establishments only. 318-4. Uses Not Permitted. Cable tray systems shall not be used in hoistways or where subject to severe physical damage. Cable tray systems shall not be used in environmental air-handling spaces except to support wiring methods recognized in Section 300-22(c). 318-5. Construction Specifications. (a) Strength and Rigidity. Cable trays shall have suitable strength and rigidity to provide adequate support for all contained wiring. (b) Smooth Edges. Cable trays shall not have sharp edges, burrs, or projections that may damage the insulation or jackets of the wiring. (c) Corrosion Protection. Cable trays shall be made of corrosionresistant material or, if made of metal, shall be adequately protected against corrosion. (d) Side Rails. Cable trays shall have side rails or equivalent structural members. (e) Fittings. Cable trays shall include fittings or other suitable means for changes in direction and elevation of runs. (f) Nonmetallic Cable Tray. Nonmetallic cable trays shall be made of flame-retardant material. 318-6. Installation. (a) Complete System. Cable trays shall be installed as a complete system. Field bends or modifications shall be so made that the electrical continuity of the cable tray system and support for the cables shall be maintained. (FPN): It is the intent to permit discontinuous segments and termination of cable tray installations where the system provides for the support of cables in accordance with their corresponding articles and where adequate bonding is provided in the cable tray system design. (b) Completed Before Installation. Each run of cable tray shall be completed before the installation of cables. (c) Supports. Supports shall be provided to prevent stress on cables where they enter raceways or other enclosures from cable tray systems. 70-200 NATIONAL ELECTRICAL CODE (d) Covers. In portions of runs where additional protection is required, covers or enclosures providing the required protection shall be of a material compatible with the cable tray. (e) Multiconductor Cables Rated 600 Volts or Less. Multiconductor cables rated 600 volts or less shall be permitted to be installed in the same cable tray. (f) Cables Rated Over 600 Volts. Cables rated over 600 volts shall not be installed in the same cable tray with cables rated 600 volts or less. Exception No. 1: Where separated by a solid fixed barrier of a material compatible with the cable tray. Exception No. 2: Where cables over 600 volts are Type MC. (g) Through Partitions and Walls. Cable trays shall be permitted to extend transversely through partitions and walls or vertically through platforms and floors in wet or dry locations where the installations, complete with installed cables, are made in accordance with the requirements of