What are the holes in a cable tray called

Perforated cable trays typically have holes occupying at least 30% of the tray base area, as defined by BS 7671.

Standard Requirements

According to BS 7671, a perforated cable tray must have a regular pattern of holes that occupy at least 30% of the base area. This ensures adequate ventilation and heat dissipation for cables, allowing the tray to meet current-carrying capacity requirements using Reference Method E or F. Trays with less than 30% perforation are treated as unperforated, with reduced ampacity considerations (Reference Method C) for the cables installed.

Practical Considerations

In practice, most standard perforated trays have less than 25% of their weight removed by holes, which may limit airflow if cables cover the perforations. Achieving more than 30% perforation often requires basket or ladder-type trays, as punching a flat sheet beyond this threshold can compromise structural integrity. Ladder trays: Open construction with rungs, providing excellent ventilation and high ampacity.

Ventilated trough trays: Solid bottom with slots or holes, offering moderate ventilation. Wire mesh (basket) trays: High perforation, flexible, and ideal for data or low-voltage cables.

Design Implications

The percentage of holes affects: Airflow and cooling: Higher perforation improves heat dissipation. Cable support: Excessive perforation may reduce mechanical strength. Compliance: Ensures adherence to standards like BS 7671 or NEC 392.

For most installations, a 30–40% perforation is typical, balancing ventilation and structural stability. For very high airflow needs, basket trays are preferred, as they can exceed 30% open area without compromising support. In summary, perforated cable trays are designed with at least 30% of the base area as holes, but practical designs often range from 25% to 40%, depending on tray type and application.