Non-standard equipment electrical wiring cable trays

Non-standard electrical wiring in cable trays requires careful selection of tray types, cable ratings, spacing, and EMC considerations to ensure safety and compliance with NEC and engineering best practices.

Cable Tray Selection and Materials

Cable trays are open or enclosed structures designed to support and route electrical cables. For non-standard installations, tray material and design must match environmental and mechanical requirements. Common materials include aluminum, steel, stainless steel, and FRP (fiberglass reinforced plastic), chosen for corrosion resistance, mechanical strength, and weight considerations . Specialized trays, such as wire-mesh or channel trays, can provide additional support for light instrumentation cables or aesthetic applications . Solid or ventilated bottoms may be used depending on heat dissipation and electromagnetic interference (EMI) concerns .

Cable Types and Ratings

Only UL-listed, tray-rated cables should be used, even in non-standard setups. Common types include:

• Type TC (Tray Cable): Power and control circuits, rated 600V, suitable for industrial and hazardous locations, with crush and impact resistance (TC-ER) allowing short unsupported runs to equipment .
• Type ITC (Instrumentation Tray Cable): Shielded or unshielded, for sensitive instrumentation and control applications .
• Metal-Clad (MC) cables: Can be used for power circuits in trays, providing additional mechanical protection . Cables must be segregated by function to prevent EMI, with high-power and low-power cables separated according to NEC guidelines .

Installation Considerations

Non-standard wiring often requires custom routing, bends, or transitions. Key practices include:

• Maintaining minimum bend radius to prevent conductor damage .
• Securing cables at intervals (typically ≤6 feet for TC-ER) when leaving the tray .
• Fill limits: Power cables ≤40% of tray cross-section, control cables ≤50% .
• Clearances: Maintain at least 12 inches vertical clearance above trays for access and maintenance .
• Grounding: Metallic trays can serve as equipment grounding conductors if compliant with NEC .
• Segregation and EMC: Non-standard layouts must consider electromagnetic compatibility, especially near sensitive equipment, using shielding, spacing, or grounded metallic barriers .

Exceptional and Non-Standard Practices

In specialized facilities, such as research or industrial plants, exceptions to standard practices may be allowed under strict engineering review:

• Deviations from standard tray routing or cable types must be approved by electrical engineering authorities .
• Non-standard supports or architectural constraints may require custom tray designs or reinforced supports .
• All exceptions must not compromise safety, EMC performance, or compliance with local regulations .

Best Practices

• Use competent personnel familiar with electrical installation and safety standards .
• Bundle and balance cables to minimize mechanical stress and maintain system integrity .
• Document all non-standard installations for future maintenance and compliance verification .
• Consider heat dissipation, accessibility, and future expansion when designing non-standard tray layouts . By following these guidelines, non-standard electrical wiring in cable trays can be safely implemented while maintaining compliance with NEC, UL, and EMC requirements, ensuring long-term reliability and safety.