MI cables in cable trays should be spaced to allow heat dissipation, prevent mechanical stress, and maintain accessibility, typically using 150–230 mm rung spacing and 150 mm vertical clearance between trays.

Horizontal and Vertical Spacing

For MI cables, which are dense and have high thermal conductivity, adequate spacing is critical to prevent overheating. In ladder or ventilated trays, a rung spacing of 6 to 9 inches (150–230 mm) is recommended to support the cables and maintain separation between layers, especially for instrumentation or control circuits . When multiple trays are stacked or installed vertically, a minimum vertical clearance of 150 mm between trays is advised. This ensures proper airflow, facilitates heat dissipation, and allows future cable additions or maintenance . Horizontal spacing between power and signal trays should generally be at least 0.5 meters, though shielding can reduce this to 0.3 meters if electromagnetic interference (EMI) is a concern .

Support Intervals

MI cables are heavier than standard PVC-insulated cables, so tray support spans should be shorter to prevent sagging. Typical support intervals for ladder trays range from 1.5 to 3 meters for straight runs, with shorter spans for heavy MI cables or long horizontal runs . For indoor installations, short-span trays are supported every 6–8 feet (1.8–2.4 meters), while intermediate spans may be 10–12 feet (3–3.6 meters) .

Tray Type Considerations

• Ladder trays: Provide excellent ventilation and are preferred for MI power cables due to heat dissipation.
• Ventilated trough trays: Suitable for medium-voltage MI cables; allow moderate airflow while offering some protection.
• Solid-bottom trays: Offer maximum protection but reduce heat dissipation; spacing may need to be increased to prevent overheating .

Additional Recommendations

• Maintain cable separation to reduce mechanical stress and EMI.
• Avoid overfilling trays; follow NEC 392 fill rules to ensure proper airflow and prevent overheating .
• Use tie-downs or cable clamps at rungs to prevent shifting, especially in vertical runs or at bends .
• Consider thermal expansion of MI cables in long runs and provide adequate spacing at bends and supports . By following these spacing and support guidelines, MI cables can be safely installed in cable trays while maintaining system reliability, thermal management, and ease of maintenance.