Cable Tray Fill / Sizing Calculator
Calculate cable tray fill ratio and determine if a tray width is adequate for the installed cables, per NEC 392 / NEMA FG1 / IEC standards.
Results
What is it?
Cable tray fill ratio is the ratio of the total cross-sectional area of installed cables to the usable tray area. NEC Article 392 limits fills: 50% for a single layer of cables in ladder tray; 40% for mixed sizes. Fill limits ensure heat dissipation, airflow, and future capacity.
How to use
Select the tray width from standard sizes and enter the usable depth (typically 50–150 mm). Enter the number of cable runs and the average outer diameter per cable. The 50% fill limit is standard — adjust for your applicable code or derating requirements.
Example scenario
10 cables of 25 mm OD in a 300 mm × 100 mm tray. Cable area = 10 × π × 12.5² = 4909 mm². Tray area = 30,000 mm². Fill = 4909/30000 = 16.4% — well within the 50% limit. The tray can accommodate up to 30 similar cables.
Pro tip
Always leave future capacity — a 30–40% fill provides room for expansion without re-routing. For higher fill ratios, apply current derating factors to cable ampacity (NEC 310.15). Separate power and control cables into different trays or use barriers to reduce electromagnetic interference.