Calculate cable tray fill per NEC 392 — ladder, solid-bottom, and ventilated trough trays with sizing examples and code requirements. NEC 392 Fill Rules by Tray Type 3. Step-by-Step Calculation Example 4. Common Mistakes to. Properly sizing your cable tray is critical for safety and compliance. IEC 61537 covers cable tray and cable ladder systems for the support and accommodation of cables, while NEC Article 392 governs cable. Cable tray types, fill rules for single-conductor and multiconductor cables, ampacity derating, separation requirements, and when to use tray vs conduit. This calculator features an interactive interface with advanced visualizations. Many different types of wire can be accommodated in cable trays, including High-voltage power lines.