National Standard for All-Copper Grounding Wire for Cable Trays

The National Electrical Code (NEC) requires that all-copper grounding conductors in cable trays be sized according to Table 250. 122 and installed to provide a continuous, low-impedance path for fault current.

NEC Requirements for Copper Grounding Conductors

The NE

C Article 250 governs grounding and bonding in electrical systems, including cable tray installations. All metallic cable trays must be grounded, whether or not they are used as the equipment grounding conductor (EGC) (NEC 250. 96).

Copper conductors are preferred for their conductivity and corrosion resistance, especially in environments where aluminum trays are used, as bare copper in aluminum trays can cause galvanic corrosion.

Sizing of Copper Grounding Wires

The size of the copper EGC is determined by the rating of the overcurrent protection device (OCPD) protecting the circuit, as specified in NEC Table 250. 122. For example, a #4 AWG copper conductor may be required for circuits protected by a 100 A breaker, while larger circuits require proportionally larger conductors.

The NE

C also permits a single conductor copper wire to serve as the common EGC for all circuits in a cable tray, provided it is properly bonded to each tray section (NEC 318-3(b)(1), Exception 2).

Installation and Bonding Practices

Bonding to Cable Tray Sections: Copper EGCs should be mechanically and electrically bonded to each or alternate cable tray sections using listed connectors to ensure continuity under fault conditions. Insulation Considerations: In aluminum trays, insulated copper conductors are recommended, with insulation removed only at bonding points to prevent corrosion. Tray as EGC: In qualifying facilities with trained personnel, the metal tray itself may serve as the EGC if it meets the minimum cross-sectional area requirements in NEC Table 392.

60(A).

Safety and Compliance

Proper grounding ensures that fault currents are safely conducted to facilitate the operation of protective devices, reducing shock hazards and equipment damage. Grounding inspections should be performed before energizing the system and after all tray sections are installed to verify continuity and compliance with NEC standards.

Summary

For cable tray systems, all-copper grounding wires must be sized according to NEC Table 250. 122, bonded to each tray section, and installed to maintain a continuous, low-impedance path. Insulated copper conductors are recommended in aluminum trays to prevent corrosion, and the tray itself may serve as the EGC in qualified facilities.

Adhering to these standards ensures safety, reliability, and NEC compliance in industrial and commercial electrical installations.