Requirements for the cross-section of fireproof cable trays

The cross-section of fireproof cable trays must be sized to support the cable load, maintain mechanical strength, and allow proper firestopping, with width, thickness, and spacing determined by cable type, quantity, and fire protection standards.

Tray Cross-Section Design

Width and Thickness: The tray width and thickness should be selected based on the number, size, and weight of cables to prevent deformation or failure under full load. Wider trays or those with larger rung spacing reduce overall strength, so manufacturers' load charts must be consulted to ensure safe support for the intended cable load . Typical ladder tray widths range from 6 to 48 inches, with rung spacings of 6, 9, 12, or 18 inches, depending on cable type and size . For small-diameter control and instrumentation cables, 6–12 inch rung spacing is recommended, while large power cables require 9-inch or wider spacing . Material Selection: Fireproof cable trays are usually made from painted or galvanized steel for indoor use, hot-dip galvanized or stainless steel for outdoor environments, and aluminum alloy or fiberglass-reinforced plastic in corrosive or high-humidity areas . The material must withstand mechanical stress and maintain integrity under fire conditions.

Fireproofing and Firestopping

Fire-Resistant Measures: Cable trays passing through walls, slabs, or entering electrical panels must be sealed with fire-rated boards, firestop packs, firestop mastic, or fire-resistant mineral wool . The gap area between firestop packs and cables should not exceed 1 cm², and packing thickness should be at least 24 cm. Large openings require a fire-resistant backing plate before sealing, and cover plates should be square, evenly painted, and properly dimensioned . Slab Penetrations: At slab penetrations, provide 20–30 mm of firestopping and install a fire-support plate at the top. Cable trays at floor level or slab penetrations should include a waterstop of at least 50 mm . All gaps inside and around metal trunking must be sealed completely to maintain fire integrity.

Additional Considerations

• Segregation of Cables: Power and signal cables should be routed separately to minimize interference .
• Bending Radius: Maintain the minimum bending radius for cables as they exit the tray to prevent damage .
• Mechanical Strength: Ensure the tray can support the full cable load without excessive deflection, especially for wide trays or those with large rung spacing .
• Installation Sequence: Fireproofing should be applied after cable routing and grounding, following proper installation sequence to ensure effectiveness . By carefully selecting the tray cross-section, material, and fireproofing measures, fireproof cable trays can safely support electrical systems while complying with fire safety standards.