Where should cable trays be grounded

All metallic cable trays must be grounded to the building's grounding system to ensure safety and compliance with NEC standards.

Key Grounding Principles

Metallic cable trays, whether steel, aluminum, or wire mesh, must be electrically continuous and connected to the facility's grounding system. This provides a low-impedance path for fault currents, protecting personnel and equipment from electric shock, fire hazards, and equipment damage due to overvoltage or insulation failure .

Grounding Locations and Methods

1. Connection to Building Grounding System: Each cable tray system should be securely bonded to the building's main grounding electrode system. This ensures that any fault current is safely directed to ground .
2. Bonding at Splice Points: All tray sections and fittings must maintain electrical continuity. Bonding jumpers should be used where mechanical connections alone do not guarantee a continuous conductive path . This is critical for wire mesh trays and other modular systems.
3. Equipment Grounding Conductor (EGC): In some installations, the cable tray itself can serve as the EGC if it meets NEC requirements, including minimum metal cross-sectional area for the expected fault current . If an EGC conductor is installed in or on the tray, it should be bonded to each or alternate tray sections using grounding clamps to prevent mechanical displacement during fault conditions .
4. Material Considerations:
   • Aluminum trays: Avoid using bare copper conductors due to potential electrolytic corrosion in moist environments. Use insulated conductors with insulation removed only at bonding points .
   • Steel trays: Should not be used as EGCs for circuits with ground-fault protection above 600 amperes; aluminum trays have a 2000-ampere limit .

Best Practices

• Ensure all tray sections are mechanically tight and electrically continuous.
• Verify grounding conductor sizing according to NEC tables to safely carry potential fault currents .
• Maintain proper separation of power and data cables to reduce electromagnetic interference while ensuring all metallic trays remain grounded .
• Regularly inspect bonding connections and continuity to prevent discontinuities that could compromise safety . By following these grounding practices, cable trays provide a reliable path for fault currents, enhance system reliability, and protect both personnel and equipment from electrical hazards .