Grounding of cable tray electrical box

Metallic cable trays must be properly grounded to ensure electrical safety, either by using the tray itself as an equipment grounding conductor (EGC) or by connecting a dedicated grounding wire.

Purpose of Grounding

Grounding a cable tray provides a safe path for stray electrical currents to flow into the earth, protecting personnel, equipment, and the electrical system from faults, surges, or shocks ( ). Proper grounding also reduces electromagnetic interference (EMI) and ensures system stability ( ).

Methods of Grounding

Using the Cable Tray as the EGC: Metallic trays can serve as the equipment grounding conductor if they meet NEC requirements for conductivity and cross-sectional area. Steel trays are limited to circuits with ground-fault protection below 600 amperes, and aluminum trays below 2000 amperes ( ). Dedicated Grounding Conductor: A separate insulated or bare conductor can be run along the tray length and bonded to each tray section using grounding clamps.

This is recommended to prevent mechanical displacement of the conductor during fault conditions ( ). Bonding Between Tray Sections: Grounding clamps or connectors should bond each tray section to maintain electrical continuity. Tin or zinc-plated connectors are preferred, especially when using insulated conductors in aluminum trays to prevent electrolytic corrosion ( ).

Materials for Grounding

Copper Wire: Excellent conductivity and corrosion resistance, commonly used for insulated or bare conductors ( ).

Hot-

Dip Galvanized Steel: Durable and corrosion-resistant, suitable for industrial environments ( ). Stainless Steel: Ideal for harsh or corrosive environments ( ).

Installation Considerations

Ensure grounding resistance is low, ideally 4 ohms or less, to maintain effective fault current paths ( ). Avoid placing bare copper conductors in aluminum trays in moist environments; use insulated conductors with exposed bonding points ( ). Maintain proper tray fill limits and separation of high-power and low-power cables to prevent overheating and EMI ( ).

Follow NE

C Article 250. 96 and 392 for grounding and bonding requirements, including minimum metal cross-sectional areas for trays used as EGCs ( ).

Best Practices

Bond alternate tray sections if continuous bonding is not feasible. Use grounding clamps to mechanically secure the conductor to prevent displacement during fault currents. Regularly inspect grounding connections for corrosion, looseness, or damage.

Select tray materials and grounding conductors based on environmental conditions and electrical load requirements ( ). Proper grounding of cable trays ensures compliance with NEC standards, enhances safety, and maintains reliable operation of electrical systems in industrial, commercial, and data center environments.