Metallic cable trays must be grounded at the start and end, with additional grounding points every 20–30 meters for trays longer than 30 meters.

NEC and General Guidelines

All metallic cable trays must be grounded according to NEC Article 250.96, even if the tray is not used as an equipment grounding conductor (EGC) itself . Grounding ensures a safe path for fault currents, preventing electric shocks, equipment damage, and fire hazards .

Grounding Frequency

• Trays 30 meters or shorter: At least two connections to the main grounding conductor are required—one at the start and one at the end .
• Trays longer than 30 meters: Additional grounding points should be installed every 20–30 meters along the tray .
• Start and end connections: Always securely connect the tray to the grounding network at both ends to maintain electrical continuity .

Grounding Methods

1. Separate EGC conductor: A bare or insulated conductor (minimum size #4 AWG) can be installed inside or attached to the tray and bonded to each or alternate tray sections using grounding clamps .
2. Cable EGCs: Multi-conductor cables with individual EGCs can be used, with the tray bonded to these conductors.
3. Tray as EGC: In some facilities, the metallic tray itself can serve as the EGC if it meets NEC cross-sectional area requirements and is properly bonded .

Material Considerations

• Avoid bare copper in aluminum trays to prevent electrolytic corrosion; use insulated conductors with exposed ends at bonding points .
• Use tin- or zinc-plated connectors for reliable mechanical and electrical connections .

Summary

To ensure safety and compliance: ground all metallic cable trays at both ends, and for trays exceeding 30 meters, add grounding points every 20–30 meters. Use proper conductors and bonding methods to maintain electrical continuity and minimize fault hazards. This approach aligns with NEC standards and best practices for industrial and commercial installations .