Requirements for Unplated Cable Trays

Unplated cable trays must meet mechanical, electrical, and installation standards to ensure safety, load-bearing capacity, and corrosion management.

Mechanical Strength

Unplated cable trays must be designed to support the weight of cables and any additional environmental loads without excessive sagging or deformation. IEC 61537 specifies load testing methods, including deflection and yield strength tests at spans commonly ranging from 1m to 2m, ensuring the tray can safely carry the intended cable load with an appropriate safety margin . Manufacturers typically provide test certificates to confirm compliance.

Corrosion Considerations

While unplated trays lack protective coatings, they must still be suitable for the intended environment. In non-corrosive indoor environments, bare steel trays may be acceptable, but in humid, coastal, or chemical-prone areas, additional corrosion protection (like galvanization or painting) is recommended to prevent structural degradation . Material selection, such as stainless steel or aluminum, can also mitigate corrosion risks.

Electrical Continuity and Grounding

Unplated metallic trays often serve as part of the grounding system. IEC 61537 requires that trays used for bonding or grounding maintain a resistance of less than 0.1 ohms across joints to safely carry fault currents . Accessories like bonding plates, jumpers, and clamps must also meet these continuity requirements. Continuity tests should be performed after installation, especially if trays are painted or coated post-fabrication.

Ventilation and Fill Ratio

Proper ventilation is essential to prevent overheating of cables. IEC 61537 recommends perforated or ventilated tray designs and specifies maximum fill ratios—typically 40% for power cables and 50% for control cables—to ensure adequate airflow and prevent overloading . Maintaining these limits is critical for thermal management and long-term cable performance.

Installation Requirements

Unplated trays must be installed according to standards such as NEC Article 392 and NEMA VE 1. Key requirements include:

• Maintaining minimum clearances (e.g., 12 inches vertical clearance for access and maintenance)
• Avoiding prohibited areas like hoistways or enclosed spaces
• Ensuring proper separation between high-power and low-power cables to reduce electromagnetic interference
• Using compatible fittings, bends, and risers for structural integrity and continuity

Summary

In essence, unplated cable trays must satisfy mechanical load capacity, electrical continuity, ventilation, and installation standards. While bare trays are acceptable in controlled environments, attention to corrosion, grounding, and proper installation is critical to ensure safety and compliance with IEC 61537, NEC 392, and NEMA VE 1 standards .