Standards for Sealing Cable Trays in Low Voltage Wiring Shafts

Cable trays in low-voltage electrical shafts must be sealed with fire-resistant materials, ensuring tight, reliable closures without visible gaps, while complying with applicable standards and installation best practices.

Firestopping and Sealing Requirements

When low-voltage cable trays pass through electrical shafts, walls, or slabs, all openings must be tightly sealed using firestopping materials to prevent fire and smoke propagation. Acceptable materials include fire-rated boards, firestop packs, firestop mastic, or fire-resistant mineral wool. For large openings, a fire-resistant backing plate should be installed before sealing to provide structural support and ensure complete coverage.

Gap limitations: The area between firestop packs and cables should not exceed 1 cm², and the packing thickness should be at least 24 cm. Metal trunking: All gaps inside and around metal cable trays or trunking must be sealed both internally and externally. Cover plates: Use square, consistently sized cover plates, painted evenly, to close openings and maintain aesthetics and safety.

Slab Penetrations

For cable trays passing through slabs in electrical shafts: Provide 20–30 mm of firestopping at the penetration. Install a fire-support plate at the top of the penetration. Ensure a waterstop of at least 50 mm at floor-level penetrations to prevent water ingress.

Technical and Safety Considerations

Cable types: Low-voltage power cables (50–1000 V AC or 120–1500 V DC) must comply with standards such as AS 1125 for conductor specifications and AS 3008 for current-carrying capacity, voltage drop, and short-circuit ratings. Control and signal cables: Must be shielded and installed in metal conduits or ducts, maintaining at least 300 mm separation from power cables to minimize electromagnetic interference. Installation sequence: Firestopping should be performed after floor and wall finishes are completed and shaft doors are installed, following a logical sequence: reserved openings → cable tray installation → conduit and cable routing → grounding → waterproofing → firestopping.

Best Practices

Maintain reasonable layout and positioning to facilitate installation and future maintenance. Ensure tight and reliable sealing without visible cracks or voids. Use appropriate fire protection materials based on the shaft environment and cable type.

Verify compliance with local standards and regulations, including Australian Standards, IEC, ISO, or other relevant codes. By following these requirements, low-voltage cable trays in electrical shafts will meet fire safety, electrical safety, and maintainability standards, ensuring both regulatory compliance and operational reliability.