Requirements for long spans of cable trays

Long-span cable trays are typically supported at intervals of 14 to 20 feet, with design and support requirements governed by NEMA, NEC, CEC, and IEC 61537 standards.

Support Span Guidelines

For long-span cable trays, the recommended support intervals are generally 14 to 20 feet, with 20 feet being the most common. Extra-long spans exceed 20 feet and may reach 20 to 40 feet in outdoor installations, such as when crossing roads or minimizing the number of expensive supports. The support span is the distance between structural supports, and the tray length should always be equal to or longer than the selected support span to maintain structural integrity.

Splice Plate Placement

Splice plates connect two sections of cable tray and are critical in long-span installations. Best practices recommend placing only one splice plate per support span to reduce stress and deflection at the joint. Matching tray length to support span helps control splice locations and ensures proper load distribution.

Load and Deflection Considerations

Cable tray systems must be designed to handle the weight of cables, environmental loads, and external forces. The distance between supports affects tray strength exponentially, so selecting a tray with adequate load rating for the chosen span is essential.

IE

C 61537 specifies mechanical strength testing, including deflection and yield strength at various spans, to ensure trays can support cables without excessive sagging.

NEM

A VE-1 and VE-2 standards provide load/span class designations for metal cable trays, harmonized with the NEC and CEC.

Material and Environmental Factors

Material selection impacts long-span performance. Steel, aluminum, stainless steel, and fiberglass trays have different strength-to-weight ratios and corrosion resistance. Outdoor or corrosive environments may require extra-long spans with stronger materials or additional protective coatings.

Thermal expansion and contraction should also be considered in long spans to prevent structural stress. Compliance with StandardsNEMA VE-1/VE-2: Defines manufacturing, installation, and load/span requirements for metal cable trays in accordance with NEC and CEC rules.

IE

C 61537: International standard for metallic cable trays, specifying construction, testing, and performance criteria, including mechanical strength and deflection limits.

U

L 568: Covers performance requirements for nonmetallic (fiberglass) cable trays.

Best Practices

Use 1/4 span support placement to minimize stress at splice locations. Ensure tray length matches or exceeds support span. Select tray material and design based on environmental conditions and load requirements.

Verify compliance with NEMA, NEC, CEC, and IEC standards for safety and long-term performance. By following these guidelines, engineers and installers can ensure structurally sound, code-compliant, and durable long-span cable tray installations.