How to position tunnel cable tray supports

Proper positioning and installation of cable tray supports in tunnels ensure safe, reliable, and code-compliant cable management while accommodating environmental and operational requirements.

Support Positioning

Support spacing is critical to maintain structural integrity and prevent sagging. For standard cable trays, supports are typically spaced every 1. 5 to 3 meters (5–10 feet) depending on tray type, material, and load.

Heavier loads or long spans may require closer spacing or additional intermediate supports. In tunnels, consider vibration, thermal expansion, and potential seismic activity when determining support intervals. Alignment and elevation are essential for smooth cable routing.

Trays should be installed level or with a slight slope to facilitate drainage and prevent water accumulation. Center-hung supports allow easier cable installation from both sides, while side-hung or wall-mounted supports may be used where ceiling space is limited.

Installation Procedure

Design and Layout: The system designer or engineer should plan the tray routing, support locations, and clearances, considering other tunnel services and local codes. Mounting Hardware: Use threaded rods, clamps, and washers to secure trays. For ladder trays, position clamps around the siderails, insert washers, and tighten hex nuts to achieve the desired elevation.

Double Tray Support: When supporting adjacent trays, use double clamps (DC) to maintain proper spacing and alignment. Material Selection: Choose corrosion-resistant materials such as galvanized steel, stainless steel, aluminum, or GRP depending on tunnel humidity, chemical exposure, and fire safety requirements. Cable Protection: Ensure trays maintain minimum bend radius for cables and avoid sharp edges.

Solid or ventilated covers may be used to protect sensitive instrumentation or control cables.

Safety and Compliance

Follow BS E

N 61537 for cable tray systems and BS 6946 for channel supports in the UK, or the National Electrical Code (NEC) in North America. Do not use trays as walkways or for personnel support; they are designed solely for cable support. Ensure all installation personnel are qualified and familiar with electrical safety procedures.

Consider fire, water ingress, and emergency power continuity in tunnel environments, using dual power supplies or UPS systems for critical circuits.

Maintenance Considerations

Inspect supports periodically for corrosion, loosening, or deformation. Maintain clear access for cable addition or replacement. Document tray layout and support positions for future maintenance and upgrades.

By following these guidelines, tunnel cable tray systems can achieve structural stability, operational reliability, and compliance with safety standards, ensuring long-term performance in challenging underground environments.