Sealing of cable trays in low-voltage electrical 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.