Cable Tray Grounding Standards

All metallic cable trays must be grounded to ensure electrical safety, with specific NEC guidelines for using the tray as an equipment grounding conductor (EGC).

General Grounding Requirements

All metallic cable trays are required to be grounded according to NEC Article 250. 96, regardless of whether the tray itself is used as an EGC ( ). Grounding ensures that any fault current is safely conducted to earth, reducing the risk of electric shock or fire.

Equipment Grounding Conductor (EGC) OptionsThere are three primary methods for providing an EGC in a cable tray system ( ): EGC conductor in or on the cable tray – a separate insulated or bare conductor runs along the tray.

Individual EG

C in each multi-conductor cable – each cable includes its own grounding conductor. Cable tray itself as the EGC – allowed only in qualifying facilities and subject to NEC Section 318-3(c) limitations. If an EGC cable is installed in or on the tray, it is desirable to bond it to each or alternate tray sections using grounding clamps.

This provides both electrical continuity and mechanical anchoring to prevent the EGC from being displaced under fault current conditions ( ).

Material Considerations

Aluminum trays: Avoid using bare copper EGCs due to potential electrolytic corrosion in moist environments. Use insulated conductors with insulation removed only at bonding points, and use tin- or zinc-plated connectors ( ). Steel trays: Can be used as EGCs but are limited for circuits with ground-fault protection above 600 A.

Aluminum trays are limited above 2000 A ( ).

Cross-

Sectional Area Requirements

The minimum metal area of the tray is specified in NEC Table 392. 60(A) to ensure the tray can safely carry fault currents if used as an EGC. Ladder or trough trays require the total cross-sectional area of both side rails, while channel trays require the minimum metal area of the tray body ( ).

Bonding and Electrical Continuity

Cable trays must be electrically continuous, even if not mechanically continuous, and bonding should comply with NEC Section 250-75. Proper bonding ensures low impedance paths for fault currents and helps protective devices operate quickly to clear faults ( ).

Wire Mesh Cable Trays

For wire mesh trays supporting cables with built-in EGCs or signal cables, a separate grounding conductor is usually not required, but the tray should maintain a low-impedance path to a non-system ground to reduce noise and stray currents ( ).

Summary

Ground all metallic cable trays per NEC 250. 96. Use an EGC in the tray, in each cable, or the tray itself (qualifying facilities only).

Bond EG

Cs to tray sections with clamps for safety and mechanical stability. Observe material limitations and avoid bare copper in aluminum trays. Ensure tray cross-sectional area meets NEC requirements for fault current capacity.

Maintain electrical continuity and low-impedance paths for effective fault clearing.