How to seal up cable trays in vertical shafts

Cables in vertical shaft trays should be sealed using firestop packs, intumescent caulks, or watertight seals to ensure fire protection, water resistance, and mechanical stability.

Firestopping in Vertical Shafts

When cables pass through vertical shafts, walls, or slabs, all openings must be tightly sealed with firestopping materials to prevent fire and smoke spread. Common materials include fire-rated boards, firestop packs, firestop mastic, and fire-resistant mineral wool. For large openings, a fire-resistant backing plate should be installed before sealing.

Firestop packs should be placed in an orderly sequence, ensuring that gaps between packs and cables do not exceed 1 cm² and packing thickness is sufficient, typically not less than 24 cm. All gaps inside and around metal trunking must be sealed both internally and externally, and cover plates should be square, evenly painted, and properly fitted.

Watertight Sealing

For vertical cable tray runs, especially in concrete pull boxes or outdoor/wet environments, watertight penetration is critical. Individual cable seals using pressure-fit seals are recommended for a truly watertight solution. Specialist products like Roxtec or Hawke transit systems can be used if installed correctly.

Alternatively, a dam can be built around the cable penetrations and filled with flowable silicone, such as Dow Corning 734, which fills all crevices and cures to form a watertight barrier.

Mechanical Fixation and Cable Management

Vertical cable installations must account for cable weight and tension. Use high-tensile steel wire armor, pulling grips, or socks to prevent cable rupture during installation. Fail-safe mechanisms should be in place to prevent free fall in case of a pulling wire failure.

Once installed, cables should be properly fixed with mounting brackets, clamps, or cleats that maintain constant lateral clamping force, avoiding slippage or mechanical deformation due to thermal expansion or load cycling.

Installation Sequence

Complete floor and wall finishes in the shaft and install shaft doors. Install cable trays and busways, ensuring proper alignment. Route cables carefully, considering weight and bend radius.

Apply grounding and waterproofing measures. Seal all penetrations with firestop packs, mastic, or watertight seals. Install cover plates or protective barriers to complete the seal.

Key Considerations

Ensure no closed loops of ferromagnetic steel in the shaft to avoid interference. Maintain minimum bend radius for cables exiting trays. Use UL-listed firestop systems and follow manufacturer instructions for compliance.

Plan installation carefully to allow for maintenance and future cable additions. By combining firestopping, watertight sealing, and mechanical fixation, vertical shaft cable trays can be safely and effectively sealed, ensuring compliance with safety standards and long-term reliability.