Inside Width o

f Cable Tray

Maximum Allowable Fill Area for Single-Conductor

Cables in Ladder or Ventilated Trough Cable Trays

Column 1 Column 2 a

Applicable for 392.10(A)(3) Only

Applicable for 392.10(A)(2) Only

mm mm 2 in.2

in.

mm2 in.2

150 6 4,200 6.5 4,200 - (28 Sd) b 6.5-(1.1 Sd) b

225 9 6,100 9.5 6,100-(28 Sd) 9.5-(1.1 Sd)

300 12 8,400 13.0 8,400 - (28 Sd) 13.0-(1.1 Sd)

450 18 12,600 19.5 12,600 - (28 Sd) 19.5-(1.1 Sd)

600 24 16,800 26.0 16,800 - (28 Sd) 26.0-(1.1 Sd)

750 30 21,000 32.5 21,000-(28 Sd) 32.5-(1.1 Sd)

900 36 25,200 39.0 25,200 - (28 Sd) 39.0-(1.1 Sd)

The maximum allowable fill areas in Column 2 shall be calculated. For example, the maximum allowable fill, in mm 2, for a 150 mm wide cable tray in Column 2 shall be 4200 minus (28 multiplied by Sd) [the maximum allowable fill, in square inches, for a 6-in. wide cable tray in Column 2 shall be 6.5 minus (1.1 multiplied by Sd)].

The term Sd in Column 2 is equal to the sum of the diameters, in mm, of all cables 507 mm 2 (in inches, of all 1000 kcmil) and larger single- conductor cables in the same ladder or ventilated trough cable tray with small cables.

392.11 Ampacity of Cables, Rated 2000 Volts or Less, in Cable Trays.

(A) Multiconductor Cables. The allowable ampacity of multiconductor cables, nominally rated 2000 volts or less, installed according to the requirements of 392.9 shall be as given in Table 310.16 and Table 310.18, subject to the provisions of (1), (2), (3), and

310.15(A)(2).

(1) The derating factors of 310.15(B)(2)(a) shall apply only to multiconductor cables with more than three current-carrying conductors. Derating shall be limited to the number of current-carrying conductors in the cable and not to the number of conductors in the cable tray.

(2) Where cable trays are continuously covered for more than 1.8 m (6 ft) with solid unventilated covers, not over 95 percent of the allowable ampacities of Table 310.16 and Table 310.18 shall be permitted for multi-conductor cables.

(3) Where multiconductor cables are installed in a single layer in uncovered trays, with a maintained spacing of not less than one cable diameter between cables, the ampacity shall not exceed the allowable ambient temperature-corrected ampacities of multiconductor cables, with not more than three insulated conductors rated 0 through

2000 volts in free air, in accordance with 310.15(C).
FPN: See Table B.310.3.

(B) Single-Conductor Cables. The allowable ampacity of single-conductor cables shall be as permitted by

310.15(A)(2). The derating factors of 310.15(B)(2)(a) shall not apply to the ampacity of cables in cable trays. The ampacity of single-conductor cables, or single conductors cabled together (triplexed, quadruplexed, etc.), nominally rated 2000 volts or less, shall comply with the following:

(1) Where installed according to the requirements of

392.10, the ampacities for 600 kcmil and larger
single-conductor cables in uncovered cable trays
shall not exceed 75 percent of the allowable
ampacities in Table 310.17 and Table 310.19. Where cable trays are continuously