4, the conductors shall be installed in groups consisting of not

more than one conductor per phase or neutral to prevent current unbalance in the paralleled conductors due to inductive reactance. Single conductors shall be securely bound in circuit groups to prevent excessive movement due to fault-current magnetic forces. Exception: Where single conductors are cabled together, such as triplexed assemblies. 70-202 NATIONAL ELECTRICAL CODE 318-9. Number of Multiconductor Cables, Rated 2000 Volts or Less, in Cable Trays. The number of multiconductor cables, rated 2000 volts or less, permitted in a single cable tray shall not exceed the requirements of this section. The conductor sizes herein apply to both aluminum and copper conductors. (a) Any Mixture of Cables. Where ladder or ventilated trough cable trays contain multiconductor power or lighting cables, or any mixture of multiconductor power, lighting, control, and signal cables, the maximum number of cables shall conform to the following: (1) Where all of the cables are No. 4/0 or larger, the sum of the diameters of all cables shall not exceed the cable tray width, and the cables shall be installed in a single layer. (2) Where all of the cables are smaller than No. 4/0, the sum of the cross-sectional areas of all cables shall not exceed the maximum allowable cable fill area in Column 1 of Table 318-9, for the appropriate cable tray width. (3) Where No. 4/0 or larger cables are installed in the same cable tray with cables smaller than No. 4/0, the sum of the cross-sectional areas of all cables smaller than No. 4/0 shall not exceed the maximum allowable fill area resulting from the computation in Column 2 of Table 318-9, for the appropriate cable tray width. The No. 4/0 and larger cables shall be installed in a single layer, and no other cables shall be placed on them. (b) Multiconductor Control and/or Signal Cables Only. Where a ladder or ventilated trough cable tray, having a usable inside depth of 6 inches (152 mm) or less, contains multiconductor control and/or signal cables only, the sum of the cross-sectional areas of all cables at any cross section shall not exceed 50 percent of the interior cross-sectional area of the cable tray. A depth of 6 inches (152 mm) shall be used to compute the allowable interior cross-sectional area of any cable tray that has a usable inside depth of more than 6 inches (152 mm). (c) Solid Bottom Cable Trays Containing Any Mixture. Where solid bottom cable trays contain multiconductor power or lighting cables, or any mixture of multiconductor power, lighting, control, and signal cables, the maximum number of cables shall conform to the following: (1) Where all of the cables are No. 4/0 or larger, the sum of the diameters of all cables shall not exceed 90 percent of the cable tray width, and the cables shall be installed in a single layer. (2) Where all of the cables are smaller than No. 4/0, the sum of the cross-sectional areas of all cables shall not exceed the maximum allowable cable fill area in Column 3 of Table 318-9 for the appropriate cable tray width. (3) Where No. 4/0 or larger cables are installed in the same cable tray with cables smaller than No. 4/0, the sum of the cross-sectional areas of all cables smaller than No. 4/0 shall not exceed the maximum allowable fill area resulting from the computation in Column 4 of Table 318-9 for the appropriate cable tray width. The No. 4/0 and larger cables shall be installed in a single layer, and no other cables shall be placed on them. ARTICLE 318 - CABLE TRAYS 70-203 (d) Solid Bottom Cable Tray Multiconductor Control and Signal Cables Only. Where a solid bottom cable tray, having a usable inside depth of 6 inches (152 mm) or less, contains multiconductor control and/or signal cables only, the sum of the cross-sectional areas of all cables at any cross section-shall not exceed 40 percent of the interior cross-sectional area of the cable tray. A depth of 6 inches (152 mm) shall be used to compute the allowable interior cross-sectional area of any cable tray that has a usable inside depth of more than 6 inches (152 mm). Table 318-9. Allowable Cable Fill Area for Multiconductor Cables in Ladder, Ventilated Trough, or Solid Bottom Cable Trays for Cables Rated 2000 Volts or Less Maximum Allowable Fill Area in Square Inches for Multiconductor Cables Ladder or Ventilated Trough Solid Bottom Cable Trays, Cable Trays, Section 318-9(a)