Cable Tray Fill Calculator

Calculate minimum cable tray width and allowable fill area for ladder, ventilated, and solid bottom trays per NEC Article 392 and §392.22.

NEC edition

Inputs

cables
in
cables
in

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⚡ Test your knowledge
NEC Article 220 was renumbered in the 2026 code cycle. What is the new article number?
  • A. Art. 100
  • B. Art. 120
  • C. Art. 200
  • D. Art. 230
💡 NEC 2026 renumbered Article 220 (Branch-Circuit, Feeder, and Service Calculations) to Article 120.
Energy Management Systems were moved from Article 750 to which article in NEC 2026?
  • A. Art. 100
  • B. Art. 125
  • C. Art. 130
  • D. Art. 150
💡 NEC 2026 moved Energy Management Systems from Article 750 to Article 130.
Which NEC standard size overcurrent device comes after 90A?
  • A. 95A
  • B. 100A
  • C. 110A
  • D. 105A
💡 Per NEC §240.6(A), the standard sizes are …90, 100, 110, 125… There is no 95A standard size.

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How it works & the NEC rules behind it

Under NEC Article 392 (§392.22), sizing a cable tray depends on the tray type (ladder, ventilated trough, or solid bottom) and whether the cables installed are multiconductor or single-conductor.

NEC §392.22 Sizing Rules:

  • 1. Multiconductor Cables 4/0 AWG or Larger (§392.22(A)(1)(a)): Must be installed in a single layer. The minimum inside tray width must equal or exceed the sum of the cable outside diameters (OD).
  • 2. Multiconductor Cables Smaller than 4/0 AWG (§392.22(A)(1)(b)): Total cable cross-sectional area cannot exceed the maximum allowable fill area specified in NEC Table 392.22(A) (Column 1).
  • 3. Solid Bottom Cable Trays (§392.22(A)(3)): Allowable fill area is reduced (approximately 75% of ventilated ladder capacity).
  • 4. Single Conductor Cables (§392.22(B)): For single conductors 250 kcmil through 900 kcmil, the sum of cable areas must not exceed Table 392.22(B)(1) limits. 1000 kcmil and larger must be in a single layer.
  • 5. Control & Instrumentation Cables: Limited to 50% fill area for ladder/ventilated trays and 40% fill area for solid bottom trays.

Formulas & equations

Single Cable Cross-Section Area = π × (Diameter ÷ 2)² Ladder Allowable Area (sq in) = Tray Width (in) × Fill Constant (NEC Table 392.22(A)) Cable Tray Fill (%) = (Total Cable Area ÷ Max Allowable Area) × 100%

NEC reference table

Inside Tray Width Ladder / Ventilated Max Fill (sq in) Solid Bottom Max Fill (sq in) Control Cable Max Fill (50%)
6 inches7.0 sq. in.5.5 sq. in.9.0 sq. in. (3" depth)
9 inches10.5 sq. in.8.0 sq. in.13.5 sq. in.
12 inches14.0 sq. in.11.0 sq. in.18.0 sq. in.
18 inches21.0 sq. in.16.5 sq. in.27.0 sq. in.
24 inches28.0 sq. in.22.0 sq. in.36.0 sq. in.
30 inches35.0 sq. in.27.5 sq. in.45.0 sq. in.
36 inches42.0 sq. in.33.0 sq. in.54.0 sq. in.

*Source: NEC Table 392.22(A) (Allowable Fill Area for Multiconductor Cables).

Worked example, step by step

Example: Sizing Ladder Tray for 12 Multiconductor Power Cables

Cables: 8 cables with 0.85" OD and 4 cables with 1.15" OD.

  • 1. Calculate Areas: 8 × [π × (0.85/2)²] = 4.54 sq in; 4 × [π × (1.15/2)²] = 4.15 sq in.
  • 2. Total Cable Area: 4.54 + 4.15 = 8.69 sq. inches.
  • 3. Table 392.22(A) Lookup: A 6" ladder tray allows 7.0 sq in (too small). A 9" ladder tray allows 10.5 sq in (8.69 ≤ 10.5).
  • 4. Fill Percentage: (8.69 ÷ 10.5) × 100% = 82.8% fill. Specify minimum 9" Wide Ladder Cable Tray.

Frequently asked questions

Under NEC §392.20(B), cables rated over 600V (or 1000V in newer editions) cannot be installed in the same cable tray with cables rated 600V or less, unless separated by a solid, fixed barrier of material compatible with the tray.

Under NEC §392.22(A)(1)(a), multiconductor cables containing conductors 4/0 AWG or larger must be installed in a single layer with no stacking. The minimum tray width must equal the sum of all individual cable outer diameters (OD).

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