Find the minimum cable tray width for multiconductor cables using NEC 392.22(A) for ladder, ventilated trough and solid-bottom trays — or size by percent fill of the tray cross-section, as most IEC project specifications do. Enter cable diameters in mm or inches.
Fill only. Check cable ampacity derating for grouping in tray (NEC 392.80 / IEC 60364-5-52), tray load rating and support span separately. Single-conductor cables follow NEC 392.22(B), which this tool does not cover.
| Width | Allowed | Used | Utilization | Status |
|---|
The NEC treats cable tray differently from conduit. Instead of a single percentage, it splits cables into two groups:
| Inside width | Ladder / vent. — col. 1 | Ladder / vent. — col. 2 (mixed) | Solid — col. 3 | Solid — col. 4 (mixed) |
|---|---|---|---|---|
| 6″ (150 mm) | 7.0 | 7.0 − 1.2 Sd | 5.5 | 5.5 − Sd |
| 12″ (300 mm) | 14.0 | 14.0 − 1.2 Sd | 11.0 | 11.0 − Sd |
| 18″ (450 mm) | 21.0 | 21.0 − 1.2 Sd | 16.5 | 16.5 − Sd |
| 24″ (600 mm) | 28.0 | 28.0 − 1.2 Sd | 22.0 | 22.0 − Sd |
| 30″ (750 mm) | 35.0 | 35.0 − 1.2 Sd | 27.5 | 27.5 − Sd |
| 36″ (900 mm) | 42.0 | 42.0 − 1.2 Sd | 33.0 | 33.0 − Sd |
Sd = sum of the diameters (in) of the 4/0 AWG and larger cables in the same tray.
IEC 61537 defines tray systems but no fill rule, so specifications set their own — typically 40–50% of the usable cross-section (width × load depth), sometimes with a stated spare capacity. The percent method in this tool adds up every cable's area, π × D² ÷ 4, and compares it with that limit.
20 control cables of 15 mm OD and 4 power cables of 50 mm OD (4/0 AWG class).
A tray that passes fill can still be wrong. Cables in tray are derated for grouping, the tray has a load rating per metre for its support span, and power and control cables are often required in separate trays or with a barrier. Size the conductors with the Cable Size Calculator and conduit runs with the Conduit Fill Calculator.
Under NEC 392.22(A), add the diameters of cables 4/0 AWG and larger and compare them with the tray width, and add the cross-sectional areas of smaller cables and compare them with the allowable fill area in Table 392.22(A). On IEC projects, total cable area is usually limited to 40–50% of the tray cross-section.
14.0 in² for multiconductor cables smaller than 4/0 AWG. With large cables in the same tray it drops to 14.0 − 1.2 × Sd, where Sd is the sum of their diameters.
Large power cables carry high current and generate significant heat. Laying them side by side in one layer lets that heat escape; stacking them would trap it and overheat the insulation.
No. Single-conductor cables follow NEC 392.22(B), which uses different rules for 1000 kcmil and larger and for 1/0 to 4/0 AWG conductors. This tool covers multiconductor cables only.
IEC 61537 does not set one, so project specifications do. 40% to 50% of the usable tray cross-section is common, often with a requirement for 20–25% spare capacity.
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