Calculation of Fireproof Sealing for Cable Trays Penetrating Walls

Fireproof sealing of cable trays requires using UL-listed firestop materials, maintaining proper gap dimensions, and following installation sequences to achieve the wall's fire rating.

Key Principles

Firestopping is essential to maintain the integrity of fire-rated walls and prevent the spread of fire, smoke, and heat through cable tray penetrations. All penetrations must be sealed tightly without visible cracks or voids, and the sealing must match or exceed the fire rating of the wall or slab .

Material Selection

• Firestop packs or pillows: Commonly used are 3M Fire Barrier Pillows or Grace KBS Sealbags, which expand under heat to seal gaps .
• Firestop mastic or caulk: Intumescent caulks like IC 15WB can be applied around cables and trays to block heat and smoke .
• Fire-resistant mineral wool or boards: Used as backing for large openings to support firestop materials .
• Modular sealing systems: Roxtec frames allow flexible, certified sealing for multiple cables and future expansions .

Gap and Dimension Guidelines

• Openings should be approximately 6 inches larger than the cable tray dimensions to accommodate firestop bags or pillows .
• Gap area between firestop packs and cables should not exceed 1 cm², and packing thickness should be at least 24 cm .
• For slab penetrations, provide 20–30 mm of firestopping and install a fire-support plate at the top .
• For large openings, a fire-resistant backing plate should be installed before sealing .

Installation Sequence

1. Reserve openings in walls or slabs for cable trays.
2. Install busways, distribution boxes, conduits, and route cables.
3. Complete grounding and waterproofing steps.
4. Apply firestopping materials in an orderly sequence, ensuring all gaps inside and around metal trunking are sealed both internally and externally .
5. Install cover plates that are square, consistent in size, and painted evenly to close the opening .
6. Schedule firestop installation toward the end of the project to allow cable installation first .

Additional Considerations

• Intumescent coatings may be applied to metal trays to prevent heat conduction through the wall .
• Maintain a firestop maintenance register to track all penetrations and ensure ongoing compliance .
• Temporary sealing with heat-expanding sacks can be used during construction before final firestop installation . By following these guidelines, cable tray penetrations can be effectively sealed to maintain fire-rated wall integrity, comply with UL standards, and ensure safety during a fire event .