Latest Calculation Rules for Cable Tray Supports

Cable tray supports must be calculated based on tray type, load, span, and compliance with IEC 61537 and BS 7671 standards, using defined spacing formulas and safety considerations.

Key Standards and Guidelines

IEC 61537 is the international benchmark for metallic cable tray systems, covering mechanical strength, corrosion resistance, electrical continuity, fire resistance, ventilation, and installation compatibility . Compliance ensures trays can safely carry cable loads over time and maintain system integrity. BS 7671 provides additional guidance on mechanical stresses, support intervals, and fire-resistant support requirements, emphasizing that cables must not experience undue strain or risk premature failure .

Support Spacing Principles

Support spacing depends on tray type, material, load, and installation environment:

• Ladder trays: Typically 1.5–3 meters between supports depending on load and cable weight .
• Perforated or solid-bottom trays: May require closer spacing due to reduced structural rigidity .
• Vertical runs: Supports should follow vertical spacing rules; for long vertical runs exceeding 32 meters, strain relief sections are recommended, offset by at least 2 cable diameters per section .
• Bends and elbows: Supports must be placed on either side of bends, with the internal radius not less than the minimum bending radius of the cable .

Calculation Formula

The number of supports can be calculated using: Support Quantity = Total Tray Length ÷ Support Spacing + 1 For example, a 20-meter tray with 2-meter spacing requires: 20 ÷ 2 + 1 = 11 supports .

Material and Environmental Considerations

• Supports must be made of materials compatible with the tray (steel, stainless steel, or aluminum) and resistant to corrosion, especially in marine or chemical environments .
• Fire-resistant supports are mandatory for all cable types to prevent premature failure during fire events .
• Coatings or galvanization may be applied to improve durability and prevent contact corrosion in humid or contaminated atmospheres .

Practical Installation Notes

• Measure each tray section separately, including elbows, tees, and crossovers .
• Ensure proper ventilation and fill ratio to prevent overheating and maintain cable performance .
• Use strain relief sections for long vertical runs to reduce mechanical stress on terminations .
• Verify compliance with local regulations and CE, UL, or other certification requirements for the specific tray system . By following these rules, engineers can ensure safe, efficient, and code-compliant cable tray installations that maintain structural integrity and electrical safety over the system's lifetime.