Grounding for galvanized cable trays

Galvanized cable trays must be grounded to ensure electrical safety, using mechanical connections or bridging conductors to maintain continuity and prevent corrosion.

Key Grounding Principles

All metallic cable trays, including galvanized types, must be grounded regardless of whether they serve as the equipment grounding conductor (EGC) or not, in accordance with NEC Article 250.96 and Article 392 . Grounding provides a safe path for fault currents, reducing the risk of electric shock, equipment damage, or fire .

Methods for Grounding Galvanized Cable Trays

1. Using the Tray as the EGC Galvanized trays can serve as the EGC if they are electrically continuous and properly bonded at all splice points. This requires secure mechanical connections between tray sections, typically using galvanized connecting plates with at least two bolts per end, locknuts, or lock washers. In vibrating environments, spring washers are recommended to maintain reliable contact .
2. Bridging Conductors For additional safety, a tinned copper stranded wire or galvanized flat steel can be used to bridge tray sections, especially if the tray is painted or coated, which can insulate and reduce conductivity. The bridging conductor should be crimped with tinned copper lugs at both ends and connected to the main grounding system .
3. Connection to Main Grounding System The tray should be connected to the building's main grounding conductor at the start and end of the tray run. For tray lengths up to 30 meters, at least two connections to the main grounding conductor are recommended to ensure low-resistance paths .

Material Considerations

• Galvanized Steel: Zinc coating provides good conductivity and corrosion resistance, making it suitable for direct mechanical connections.
• Copper Conductors: Tinned copper is preferred for bridging or bonding to prevent galvanic corrosion when connecting to galvanized trays .
• Avoid Bare Copper in Aluminum Trays: While not directly applicable to galvanized trays, bare copper should not contact aluminum due to electrolytic corrosion risks .

Best Practices

• Ensure all tray sections are mechanically tight and electrically continuous.
• Use bonding jumpers where mechanical connections alone may not provide reliable continuity.
• Verify grounding resistance is low, ideally 4 ohms or less, to ensure effective fault current dissipation .
• Inspect connections periodically for corrosion or loosening, especially in outdoor or high-vibration environments. By following these practices, galvanized cable trays can provide a safe, reliable grounding path that complies with NEC standards and minimizes electrical hazards.