Crossing of fire cable trays and cable trays

Fire-rated cable trays must be routed with proper separation, barriers, and firestopping measures when crossing or running alongside other cable trays to ensure safety and compliance.

Separation and Routing Principles

When fire-rated or life-safety cable trays cross or run near other cable trays, physical separation or barriers are essential to maintain circuit independence and prevent fire propagation.

U

K and international standards recommend: Dedicated containment for life-safety circuits, separated from other power or signal trays by either a fire-resistant barrier or a minimum horizontal air gap, typically around 300 mm for roof-mounted installations. Segregation of power and signal cables in separate trays to reduce electromagnetic interference and maintain safety. Shortest and straightest routing to minimize cable length, reduce losses, and simplify maintenance.

Firestopping at CrossingsWhen cable trays penetrate walls, floors, or slabs, firestopping is mandatory to prevent fire and smoke spread: Use fire-rated boards, firestop packs, mineral wool, or intumescent caulks to seal openings around trays. Ensure tight packing with gaps around cables not exceeding 1 cm² and a minimum packing thickness of 24 cm for large openings. Fire pillows or moldable putty can be used for retrofitting or new installations, providing UL-listed fire containment for openings.

For vertical tray runs, covers or fire barriers are critical because open vertical trays can act like chimneys, spreading fire rapidly.

Material and Tray Considerations

Indoor trays: Painted steel or galvanized steel. Outdoor or corrosive environments: Hot-dip galvanized, stainless steel, aluminum alloy, or fiberglass-reinforced plastic. Tray width and thickness should support the cable load and prevent deformation, especially at crossings.

Use splice plates and proper hardware for structural integrity at intersections.

Practical Recommendations

Maintain circuit independence: Life-safety or fire-rated circuits should not share trays with non-critical circuits. Install fire barriers where physical separation is impractical. Regular inspection: Check grounding, tray integrity, and firestop condition periodically to ensure ongoing safety.

Follow manufacturer guidelines for firestop products, including the number of pillows, putty sticks, or caulk required for specific tray sizes. By adhering to these principles, the crossing of fire-rated cable trays with other cable trays can be performed safely, minimizing fire risk and ensuring compliance with electrical and fire safety standards.