What are the methods for fixing cable trays in low-voltage electrical shafts

Cable trays in low-voltage electrical shafts should be securely supported using wall brackets, suspended supports, or center suspensions, with proper spacing, bonding, and compliance with standards like NEC and NEMA VE 2.

Key Installation Principles

Support and Mounting: Cable trays must be mechanically supported to prevent sagging and ensure stability. Common methods include: Wall or Side Brackets: Fixed to the shaft walls to support horizontal or vertical tray runs. Brackets should be rated for the tray load and allow for minor adjustments during installation.

Suspended Supports: Rods or threaded hangers from ceilings or structural beams can support trays in vertical shafts, especially for long vertical runs. Center Suspensions: Used for wide trays or heavy cable loads to prevent bending or deflection in the middle of the span. Support Spacing: Supports should be positioned according to tray type and load.

For low-voltage applications, typical spacing is: Straight Runs: Supports at intervals recommended by the manufacturer, often every 1. 5–3 meters (5–10 ft) for light-duty trays. Elbows and Bends: Additional supports near bends, tees, or crossovers to maintain alignment and prevent stress on connectors.

Expansion Joints: Provide expansion connectors at building expansion points or long runs to accommodate thermal movement. Fastening and Bonding: Trays should be fastened using bolts, clamps, or guides that allow longitudinal movement to prevent stress on the tray and cables. All trays must be electrically bonded with jumpers at expansion joints and grounded at intervals (e.g., every 15 m or 50 ft) to maintain electrical continuity and safety.

Conduit drop-outs should be bonded to the tray using grounding bushings or compression lugs. Material and Environmental Considerations: Steel, stainless steel, or aluminum trays are commonly used, with galvanization or corrosion-resistant finishes for durability. Closed or ventilated trays may be selected based on heat dissipation, electromagnetic interference protection, and aesthetic requirements.

Compliance with Standards: Installation must follow NEC, NEMA VE 2, and manufacturer instructions for low-voltage systems. Ensure adherence to local electrical codes and standards for low-voltage cable insulation, spacing, and fire safety.

Practical Tips

Avoid placing connectors at the center of spans; position them between support points or at quarter points. Maintain minimum bend radii for cables exiting trays to prevent conductor damage. Use appropriate covers or barriers for instrumentation and control cables to protect against mechanical damage and electromagnetic interference.

By following these methods, cable trays in low-voltage electrical shafts can be installed safely, efficiently, and in compliance with relevant standards, ensuring long-term reliability and ease of maintenance.