covered for more than
1.8 m (6 ft) with solid unventilated covers, the
ampacities for 600 kcmil and larger cables shall not
exceed 70 percent of the allowable ampacities in
Table 310.17 and Table 310.19.
(2) Where installed according to the requirements of
392.10, the ampacities for 1/0 AWG through 500
kcmil single-conductor cables in uncovered cable
trays shall not exceed 65 percent of the allowable
ampacities in Table 310.17 and Table 310.19. Where cable trays are continuously covered for more than 1.8 m (6 ft) with solid unventilated covers, the ampacities for 1/0 AWG through 500 kcmil cables shall not exceed
60 percent of the allowable ampacities in Table
310.17 and Table 310.19.
(3) Where single conductors are installed in a single layer in uncovered cable trays, with a maintained space of not less than one cable diameter between individual conductors, the ampacity of 1/0 AWG and larger cables shall not exceed the allowable ampacities in Table 310.17 and Table 310.19.
Exception to (B)(3): For solid bottom cable trays the am- pacity of single conductor cables shall be determined by
310.15(C).
(4) Where single conductors are installed in a triangular or square configuration in uncovered cable trays, with a maintained free airspace of not less than 2.15 times one conductor diameter (2.15 x O.D.) of the largest conductor contained within the configuration and adjacent conductor configurations or cables, the ampacity of 1/0 AWG and larger cables shall not exceed the allowable ampacities of two or three single insulated conductors rated 0 through 2000 volts supported on a messenger in accordance with
310.15(B). FPN: See Table 310.20.
(C) Combinations of Multiconductor and Single- Conductor Cables. Where a cable tray contains a combi- nation of multiconductor and single-conductor cables, the allowable ampacities shall be as given in 392.11(A) for multiconductor cables and 392.11(B) for single- conductor cables, provided that the following conditions apply:
(1) The sum of the multiconductor cable fill area as a per- centage of the allowable fill area for the tray calculated per 392.9, and the single-conductor cable fill area as a percentage of the allowable fill area for the tray calculated per 392.10, totals not more than
100 percent.
(2) Multiconductor cables are installed according to
392.9 and single-conductor cables are installed
according to 392.10 and 392.8(D) and (E).
392.12 Number of type MV and Type MC Cables (2001
Volts or Over) in Cable Trays. The number of cables
rated 2001 volts or over permitted in a single cable tray
shall not exceed the requirements of this section.
The sum of the diameters of single-conductor and multiconductor cables shall not exceed the cable tray width, and the cables shall be installed in a single layer. Where single conductor cables are triplexed, quadruplexed, or bound together in circuit groups, the sum of the diameters of the single conductors shall not exceed the cable tray width, and these groups shall be installed in single layer arrangement.