Repeated grounding of cable trays

Metallic cable trays must be electrically continuous, bonded at all splice points, and connected to the building grounding system to ensure a safe fault current path.

Electrical Continuity and Bonding

All metallic cable trays, including ladder, trough, and wire mesh types, must maintain electrical continuity across the entire system. This means that each tray section, fitting, and splice must be bonded to eliminate gaps in conductivity. Bonding at splice points is mandatory, and bonding jumpers should be used where mechanical connections alone do not ensure reliable continuity . This repeated grounding ensures that any fault current can safely travel to the building grounding electrode system, allowing protective devices to operate effectively .

Equipment Grounding Conductor (EGC) Considerations

Cable trays can serve as the Equipment Grounding Conductor (EGC) if they meet NEC requirements, including minimum cross-sectional area for the tray metal based on fault current ratings . When a separate EGC is installed in or on the tray, it should be bonded to each or alternate tray sections using grounding clamps. This practice not only maintains electrical continuity but also mechanically secures the EGC to prevent displacement under fault conditions . For installations with multiple paralleled cables, the EGC size must be adjusted according to NEC Table 250-95 to safely carry potential fault currents .

Material and Environmental Considerations

• Aluminum trays: Avoid bare copper EGCs in moist environments to prevent electrolytic corrosion; use insulated conductors with exposed bonding points .
• Steel trays: Can serve as EGCs but are limited for circuits with high ground-fault protection ratings (above 600 A for steel, 2000 A for aluminum), .
• Wire mesh trays: Ensure bonding integrity at coated surfaces, as powder coatings can reduce conductivity .

Best Practices

1. Verify electrical continuity across all tray sections before energizing circuits.
2. Bond all splice points and fittings to maintain a continuous conductive path.
3. Use properly sized EGCs according to NEC tables, especially when trays carry multiple paralleled cables.
4. Connect the tray system securely to the building grounding electrode system.
5. Inspect periodically to ensure mechanical and electrical integrity, particularly in environments prone to corrosion or vibration . By following these repeated grounding and bonding practices, cable tray systems provide a reliable, low-impedance path for fault currents, reducing shock hazards, equipment damage, and fire risk while ensuring NEC compliance.