The recommended vertical spacing between two-layer cable trays is typically at least 12 inches (300 mm) to ensure safety, maintenance access, and minimize electromagnetic interference.

Recommended Spacing

For installations with stacked cable trays, industry standards and best practices suggest:

• Minimum vertical clearance: 12 inches (300 mm) between the top of the lower tray and the bottom of the upper tray to allow for maintenance, inspection, and airflow for heat dissipation .
• Electromagnetic interference (EMI) considerations: When power and instrumentation/control trays are stacked, maintaining at least 12 inches of separation reduces EMI and preserves signal integrity .
• Use of dividers or partitions: If space constraints prevent full separation, a metal partition can be installed between trays to further reduce interference .

Factors Affecting Spacing

1. Cable Type and Heat Generation: Ladder-type trays with high-current power cables may require additional spacing to allow proper ventilation and prevent overheating .
2. Tray Material: Metal trays can act as EMI shields, potentially allowing slightly reduced spacing, whereas non-metallic trays may require larger gaps .
3. Environmental Conditions: In hazardous or high-temperature environments, spacing may need to be increased to comply with fireproofing or explosion-proof requirements .
4. Maintenance Access: Adequate spacing ensures that technicians can safely access cables for inspection, testing, or future expansion .

Applicable Standards

• NEC 392 (USA): Specifies general cable tray installation requirements, including spacing for maintenance and safety .
• NEMA VE 1 & VE 2: Provide detailed guidance on tray construction, load capacity, and installation practices, including spacing considerations .
• IEC 61537: International standard for cable management systems, including spacing and test methods for global projects .

Practical Tips

• Always plan for future expansion by leaving extra vertical space beyond the minimum 12 inches.
• Ensure tray supports are properly rated to handle the combined weight of stacked trays.
• Consider airflow and heat dissipation when stacking trays with high-current cables to maintain ampacity and prevent derating. By following these guidelines, you can ensure that two-layer cable tray installations are safe, maintainable, and compliant with industry standards.