Define Tray Dimensions: Enter the width and depth of your planned cable tray (in mm or inches). You can also set a custom limit. Select Fill Standard: Choose 40% for power cables (NEC compliant) or 50% for. NEC Article 392 governs cable tray installations, covering tray types, fill limits, cable types permitted, and ampacity adjustments. The fill rules differ significantly between single-conductor cables and multiconductor cables, and between ladder tray and solid-bottom tray. The calculation provides necessary information to avoid cable overfilling which produces dangerous situations such as overheating, mechanical damage and reduced. Cable tray fill is the proportion of usable cross-sectional area inside a cable tray occupied by installed cables.