Comparison of Current Carrying Capacity of Ladder-Type Cable Trays and Trough-Type Cable Trays

Ladder-type and trough-type cable trays generally have equivalent current-carrying capacity when cables are installed in free-air conditions, with differences arising mainly from ventilation and heat dissipation characteristics.

Ladder-

Type Cable Trays

Design and Ventilation: Ladder trays consist of two side rails connected by rungs, creating an open structure that allows maximum airflow around cables. This design promotes efficient heat dissipation, reducing the risk of cable overheating and allowing higher current ratings in practice for densely packed or high-power cables. Applications: Ladder trays are ideal for heavy-duty power cables, long-span installations, and situations where heat buildup must be minimized.

They also facilitate easy cable entry and exit, inspection, and maintenance.

Current-

Carrying Capacity: According to BS 7671 standards, ladder trays are treated as free-air installations (Methods 32–34), meaning their CCC is calculated similarly to perforated trays under free-air conditions. The open design ensures minimal heat accumulation, which can be advantageous for high-current applications.

Trough-

Type (Perforated) Cable TraysDesign and Ventilation: Trough or perforated trays have a solid or partially perforated base, which provides better support for smaller or flexible cables and mixed services. Ventilation is less than ladder trays, so heat dissipation is slightly reduced, but perforations allow some airflow to prevent excessive temperature rise. Applications: Trough trays are preferred for control, instrumentation, and telecommunication cables where neat routing and protection are priorities.

They prevent sagging of small-diameter cables and support mixed cable types effectively.

Current-

Carrying Capacity: When using free-air reference methods, the CCC of trough-type trays is equivalent to ladder trays for the same cable formation. De-rating factors for grouping, insulation type, and ambient temperature still apply, but the tray type itself does not inherently reduce CCC.

Key Considerations

Airflow and Heat Dissipation: Ladder trays provide superior natural ventilation, which can improve practical CCC for high-power cables. Trough trays may require additional spacing or de-rating in dense installations. Mechanical Support: Ladder trays are better for long spans and heavy cables due to their rung support, while trough trays prevent sagging of smaller or flexible cables.

Installation Flexibility: Ladder trays allow cable entry/exit at any point, whereas trough trays may require planning for cable routing and support. Standards Compliance: Both tray types follow BS 7671 free-air methods for CCC calculations, so the choice is often based on mechanical and environmental considerations rather than electrical capacity alone. Conclusion: While ladder-type trays offer better ventilation and may be preferred for high-current, heavy-duty applications, both ladder and trough-type trays have equivalent current-carrying capacity under free-air conditions, with differences mainly in mechanical support, cable management, and heat dissipation efficiency.