Cable Tray Fill Calculator
Check multiconductor-cable fill in a ladder, ventilated trough, or ventilated channel cable tray against NEC 392.22(A). Enter each cable by outside diameter and the tool applies the right rule (Table 392.22(A) Column 1, Column 2, or the single-layer diameter check) and returns the minimum standard tray width. Default NEC 2020; Table 392.22(A) values are unchanged from 2017 through 2023.
How to use this calculator
- Add each multiconductor cable in the run: its outside diameter in inches (from the cable cut sheet) and how many of that cable.
- Check the "4/0 AWG or larger" box for any cable whose conductors are 4/0 or bigger. That flag decides which NEC rule applies.
- Pick a tray width to test a specific size, or leave it on Auto to get the minimum standard width that passes.
- Read the rule applied, the governing fill (area or sum of diameters), the allowable limit, and the pass/fail result.
NEC reference
Fill is computed per NEC 2020 Article 392.22(A)(1) for multiconductor cables rated 2000 V or less in ladder, ventilated trough, or ventilated channel cable trays. Where all cables are 4/0 AWG or larger, the sum of the cable diameters must not exceed the tray width in a single layer (392.22(A)(1)(a)). Where all cables are smaller than 4/0, the sum of the cable cross-sectional areas must not exceed the Column 1 allowable fill area in Table 392.22(A) (392.22(A)(1)(b)). Where the tray mixes 4/0-and-larger cables with smaller cables, the smaller cables area must not exceed Column 2, equal to Column 1 minus 1.2 times Sd, the sum of the diameters of the 4/0-and-larger cables (392.22(A)(1)(c)). Table 392.22(A) values are unchanged across the 2017, 2020, and 2023 editions.
Results are for reference only. Verify against the applicable adopted edition of the NEC and consult a licensed electrician for code compliance.
Table 392.22(A) Column 1 allowable fill area
Ladder, ventilated trough, or ventilated channel trays, multiconductor cables rated 2000 V or less. Column 1 is the maximum allowable cable cross-sectional fill area for the tray width. Column 2 (used when 4/0-and-larger cables share the tray with smaller ones) is this value minus 1.2 times Sd.
| Inside tray width (in) | Column 1 max fill area (in²) |
|---|---|
| 6 | 7.0 |
| 9 | 10.5 |
| 12 | 14.0 |
| 18 | 21.0 |
| 24 | 28.0 |
| 30 | 35.0 |
| 36 | 42.0 |
Column 1 equals the tray width times 7/6. Cable cross-sectional area is taken as the circle of the cable outside diameter, area = π × OD² / 4.
Worked example: mixed cable tray
A 12 in ladder tray carries three 4/0 multiconductor power cables (1.75 in outside diameter each) plus ten smaller control cables (0.6 in outside diameter each). Because the tray mixes 4/0-and-larger with smaller cables, Column 2 applies.
- Sd (4/0-and-larger diameters): 3 × 1.75 = 5.25 in.
- Column 1 at 12 in: 14.0 in² (Table 392.22(A)).
- Column 2 allowable: 14.0 − 1.2 × 5.25 = 7.7 in² for the smaller cables.
- Smaller-cable area: 10 × (π × 0.6² / 4) = 10 × 0.2827 = 2.83 in².
The 2.83 in² of smaller cables is well under the 7.7 in² Column 2 limit, and the 5.25 in of large-cable diameter fits a single layer in the 12 in tray, so the run passes at 12 in with room to spare. Drop to a 9 in tray and Column 2 falls to 10.5 − 6.3 = 4.2 in², which still passes; a 6 in tray gives 7.0 − 6.3 = 0.7 in², which the smaller cables would exceed.
Which rule applies
- All cables 4/0 AWG or larger. The sum of the cable diameters must not exceed the tray width, and the cables must lie in a single layer (392.22(A)(1)(a)). This is a width check, not an area check.
- All cables smaller than 4/0 AWG. The sum of the cable cross-sectional areas must not exceed the Column 1 value for the tray width (392.22(A)(1)(b)).
- A mixture of both. The 4/0-and-larger cables go in a single layer, and the smaller cables area must not exceed Column 2 = Column 1 minus 1.2 times Sd (392.22(A)(1)(c)).
This calculator selects the rule automatically from the cables you enter and their 4/0-and-larger flags, then reports the governing quantity and the applicable limit.
Scope and limitations
Version 1 covers multiconductor cables rated 2000 V or less in ladder, ventilated trough, or ventilated channel trays. It does not cover single-conductor cables (NEC 392.22(B), a different table with the 1.1 times Sd factor and a 1000 kcmil threshold), solid-bottom trays (Columns 3 and 4 with the 90 percent single-layer rule), control- and signal-cable-only trays, or cables rated over 2000 V. Cable tray ampacity and conductor derating (392.80) is a separate calculation.
Frequently asked questions
How do you calculate cable tray fill?
For multiconductor cables in a ladder or ventilated trough tray, pick the rule by cable size: all 4/0-and-larger uses a sum-of-diameters check against tray width; all smaller than 4/0 uses a sum-of-areas check against Column 1; a mixture checks the smaller cables area against Column 2 = Column 1 minus 1.2 times Sd.
What cable diameter should I enter?
Use the cable outside diameter from the manufacturer cut sheet, not the conductor AWG. Cable outside diameter varies by cable type, jacket, and manufacturer, so the published value for your exact cable is the accurate input.
Is cable tray fill a fixed percentage?
No. Unlike conduit fill, NEC 392.22(A) sets an allowable fill area in square inches per tray width rather than a single percentage. This tool reports the fill as a percentage of that allowable area so you can see how much headroom remains.
What about single-conductor cables?
Single-conductor cables are sized by NEC 392.22(B), a separate table with different thresholds (1000 kcmil) and a 1.1 times Sd Column 2 factor. This calculator handles multiconductor cables only.
Related calculators
- Conduit Fill Calculator: conductor fill for EMT, RMC, IMC, and PVC per NEC Chapter 9, Table 1.
- Conduit Size Calculator: minimum conduit trade size for a conductor bundle.
- Wire Ampacity Calculator: derated ampacity of a specific conductor.
- Cable Size Calculator: multi-conductor cable ampacity with more-than-3-conductor derating.
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