Cable tray supports should be spaced according to cable type, diameter, and installation method, typically ranging from 1.0 to 3.0 meters for horizontal runs, with closer spacing for bends and vertical sections.

Horizontal and Vertical Support Spacing

For horizontal cable tray runs, the distance between supports generally depends on the tray type, cable weight, and load. Standard practice recommends:

• Straight horizontal runs: Supports every 1.5 to 3 meters depending on tray material and cable load .
• Bends, tees, or changes in direction: Supports should be placed on either side of the bend to prevent sagging and undue stress on cables .
• Vertical runs: For long vertical sections, strain relief sections should be incorporated, typically offsetting the cable by at least 2 cable diameters per section. For runs exceeding 32 meters, a short horizontal section (at least 1 meter) is recommended to relieve tension .

Cable Diameter Considerations

The distance between fixings increases with cable diameter. Smaller cables (e.g., ≤9 mm) require closer support spacing, while larger or stiffer cables can span longer distances without sagging . Flexible cables in J-hanger or similar systems require calculations to maintain a small deflection (typically 2%) to prevent displacement during thermal expansion .

Vertical and Horizontal Clearance

• Vertical spacing between trays: Minimum 150 mm to allow airflow, maintenance, and future expansion .
• Horizontal spacing between parallel trays: Minimum 0.6 meters for general trays; 0.5 meters between power and signal trays to reduce electromagnetic interference (EMI). Shielded trays may reduce this to 0.3 meters .
• Height above ground: At least 2.2 meters for safe access .
• Top clearance from ceiling or obstructions: Minimum 0.3 meters .

Regulatory and Safety Considerations

• All cable supports must be fire-resistant to prevent premature failure in case of fire, as per BS 7671 Clause 521.10.202 .
• Supports should prevent undue strain on cables and terminations, ensuring mechanical stability and compliance with IET On-Site Guide recommendations .
• Cross-sectional fill of trays should not exceed 50% to maintain proper ventilation and prevent overheating .

Summary

Proper cable tray fixing distances depend on cable type, diameter, tray material, and installation layout. Key points include:

• Support straight runs every 1.5–3 meters.
• Place supports near bends and vertical changes.
• Maintain minimum vertical and horizontal clearances for airflow and maintenance.
• Use fire-resistant supports and avoid overfilling trays. Following these guidelines ensures mechanical stability, safety, and compliance with electrical standards while facilitating maintenance and future expansion.