Thickness requirements for ground-mounted cable trays

The thickness of metallic cable trays used as grounding conductors depends on the material and the required cross-sectional area to safely carry fault currents, as specified by NEC Table 392. 60(A).

General Guidelines

Metallic cable trays can serve as Equipment Grounding Conductors (EGC) if they meet minimum cross-sectional area requirements. The National Electrical Code (NEC) Article 392 specifies that all metallic trays must be grounded, regardless of whether they are used as EGCs, to ensure safety and prevent electrical hazards.

Minimum Cross-

Sectional Area

Steel cable trays: The total cross-sectional area of both side rails must meet the minimum specified for the intended fault current. Steel trays are generally not used as EGCs for circuits with ground-fault protection above 600 amperes. Aluminum cable trays: Aluminum trays must also meet minimum cross-sectional area requirements and should not be used as EGCs for circuits with ground-fault protection above 2000 amperes.

The cross-sectional area is calculated based on the side rails for ladder or trough trays or the metal in channel trays. This ensures the tray can safely conduct fault currents without excessive heating or damage.

Material Considerations

Steel trays: Typically hot-dip galvanized or coated to prevent corrosion. Thickness varies by manufacturer but must comply with the minimum metal area for grounding. Aluminum trays: Lightweight and corrosion-resistant, but bare copper conductors should not be used due to potential electrolytic corrosion.

Insulated conductors are recommended for bonding. Bonding: Each tray section should be bonded using grounding clamps to maintain electrical continuity and mechanical stability under fault conditions.

Practical Thickness Ranges

While exact thickness depends on tray type, material, and manufacturer, typical steel cable trays range from 1. 5 mm to 3 mm for side rails, and aluminum trays are slightly thinner due to higher conductivity, often 1. 2 mm to 2.

5 mm. Always verify with the manufacturer's specifications and NEC Table 392. 60(A) for the required cross-sectional area based on the circuit's fault current rating.

Summary

Ensure the tray material and thickness meet NEC grounding requirements. Use bonding clamps to connect tray sections and maintain continuity. Avoid bare copper in aluminum trays; use insulated conductors for bonding.

Verify the minimum cross-sectional area for the intended fault current using NEC Table 392. 60(A). By following these guidelines, cable trays can safely function as grounding conductors while complying with electrical codes and ensuring personnel safety.