Cable trays 300mm (12 inches) wide or larger typically require detailed seismic bracing, with widths between 500mm and 900mm commonly used in high-seismic installations.

Key Considerations

Tray Width and Load: The need for seismic bracing is influenced by the tray's width, cable fill, and total weight. Smaller trays (e.g., 200mm) carrying light control cables may not exceed the seismic threshold of 150 N/m (≈15 kg/m), whereas trays 300mm wide or larger often require detailed calculations to determine bracing needs . Wider trays carry more cables and have higher mass, increasing lateral and longitudinal forces during seismic events . Common Widths in Seismic Zones: In high-seismicity projects, cable trays are often 0.5m to 0.9m (20–36 inches) wide, especially for ladder-type trays supporting multiple layers of power or communication cables . These widths allow sufficient structural strength while accommodating seismic bracing systems, including diagonal braces and strut channels. Tray Type and Bracing: Ladder trays are preferred for primary distribution in seismic areas due to their stiffness and efficient weight-to-strength ratio. Perforated or trough trays may be used but require careful evaluation of support spacing and cable retention . Wire mesh or basket trays are suitable for lighter loads but need reinforced splice and support details. Seismic Bracing Design: The bracing system, including transverse and longitudinal braces, strut channels, clamps, and anchors, is often more critical than the tray width itself. Braces must resist lateral sway, longitudinal movement, and uplift, and their spacing depends on tray width, cable load, and seismic zone . Wider trays generally require more frequent or stronger bracing to maintain stability. Code Compliance: Always verify tray width and bracing requirements against local building codes, seismic design category, and project-specific structural calculations. IEC 61537 and national standards provide guidance, but final design must be engineered for the specific site and cable load .

Practical Recommendation

• Trays <300mm wide: Often do not require extensive seismic bracing if carrying light cables.
• Trays 300–500mm wide: Require careful evaluation; bracing may be needed depending on cable weight and seismic zone.
• Trays 500–900mm wide: Common in high-seismic installations; bracing is mandatory, with diagonal and longitudinal supports integrated into the design . In summary, tray width is a key factor in seismic bracing design, but the final decision must consider cable load, tray type, support spacing, and local seismic codes. Wider trays generally necessitate more robust bracing to ensure safety and compliance.