电缆桥架尺寸计算

Per IEC 60364-5-52 Table 52-2 and NEC 392.22, the fill limits are: Ladder tray ≤50%, perforated tray ≤40%, solid trough ≤35% at design current. Exceeding these limits can cause overheating and difficulty installing or removing cables.

When multiple current-carrying cables are bundled together (touching or spaced less than one cable diameter apart), their heat dissipation is reduced. IEC 60364-5-52 Table 52-17 gives derating factors: 2 cables → 0.85, 3 → 0.80, 4 → 0.75, 5 → 0.70, 6 → 0.67, etc. For more than 6 bundled cables, use separate trays or reduce current.

Higher ambient temperatures reduce cable ampacity because the thermal resistance from conductor to ambient increases. IEC 60364-5-52 Table 52-14 gives temperature correction factors: at 30°C → 1.00, 35°C → 0.94, 40°C → 0.87, 45°C → 0.80, 50°C → 0.71, 55°C → 0.61, 60°C → 0.50. For high ambient temperatures, either use larger cables or install trays in ventilated areas.

Solid trough (solid-bottom) trays provide better mechanical protection and prevent moisture ingress — suitable for single-core cables and outdoor applications. Ladder trays offer superior ventilation for multi-core cables and easier cable installation. Perforated trays are a middle ground with moderate ventilation and some mechanical protection.

XLPE (cross-linked polyethylene) has a higher maximum operating temperature (90°C continuous, 130°C emergency) compared to PVC (70°C / 80°C). This means XLPE cables can carry higher currents for the same cross-section and are preferred for high-current substation power cables. PVC is used for control cables and low-current applications.

Direct sun exposure can increase tray surface temperature by 10–20°C above ambient, significantly reducing ampacity. The tool applies an additional 0.85 sun derating factor when sun exposure is flagged. In hot climates, consider shading trays, using aluminum instead of steel (higher emissivity), or mounting trays horizontally with clearance above for airflow.