What are the fire protection requirements for cable tray supports

Cable tray supports must be fire-resistant, securely mounted, and properly spaced to prevent collapse and maintain cable integrity during a fire.

Fire-Resistant Support Materials

Cable tray supports should be made from materials that will not fail under fire conditions, such as steel, galvanized steel, or other fire-rated metals. Fire-resistant supports ensure that the cable system remains intact and functional during a fire, preventing premature collapse and maintaining critical power or communication lines . For fire-rated cables, the supports themselves must also be fire-resistant to match the cable's rating .

Support Spacing and Mechanical Stability

Supports must be installed at appropriate intervals to prevent undue mechanical strain on the cables. The spacing depends on cable type, diameter, and weight, following guidance such as the IET Selection and Erection Guidance Notes or NEC Article 392 . Supports should maintain the tray level, plumb, and securely mounted, with horizontal deviation ≤2 mm per meter and vertical deviation ≤3 mm per meter . Proper support spacing also ensures that the tray does not collapse during a fire, which is critical for safety and system reliability .

Firestopping at Penetrations

Where cable trays pass through walls, floors, or slabs, openings must be sealed with firestopping materials such as fire-rated boards, firestop packs, firestop mastic, or mineral wool . Large openings require a fire-resistant backing plate, and gaps around cables should not exceed 1 cm², with packing thickness of at least 24 cm . At slab penetrations, a fire-support plate should be installed at the top, and waterstops of at least 50 mm height are recommended at floor level .

Coatings and Protective Measures

Additional fire protection can be applied using fire-resistant coatings or tapes, such as FLAMMOTECT-A or DG-CR 0.7, which form a protective shield around cables and trays . These coatings prevent flame propagation, enhance environmental resistance, and help maintain cable functionality during a fire.

Compliance and Safety Considerations

• Ensure metallic trays are grounded if used as equipment grounding conductors .
• Maintain clearances for installation and maintenance, typically at least 12 inches above the tray .
• Separate high-power and low-power cables to reduce fire risk and electromagnetic interference .
• Avoid using cable trays in hoistways or enclosed spaces where fire could spread rapidly . By combining fire-resistant supports, proper spacing, firestopping at penetrations, and protective coatings, cable tray systems can maintain structural integrity and functionality during a fire, ensuring safety and compliance with standards .