Cable trays and cable laying grounding

Cables in metallic cable trays must be properly grounded, either by using the tray itself as an equipment grounding conductor (EGC) or by installing dedicated grounding conductors bonded to the tray, ensuring safety and NEC compliance.

Purpose of Grounding Cable Trays

Grounding cable trays is essential to: Prevent electrical shock by safely directing fault currents to ground. Reduce electrical noise and interference, protecting sensitive electronic equipment. Ensure compliance with regulations such as NEC Article 392 and Article 250, which mandate grounding and bonding of metallic trays.

Facilitate fault detection and safe maintenance operations.

Methods of Grounding

Using the Cable Tray as EGC Metallic cable trays can serve as the equipment grounding conductor if they meet NEC requirements, including sufficient metal cross-sectional area and electrical continuity. Steel trays are limited to circuits with ground-fault protection below 600 A, and aluminum trays below 2000 A. Dedicated Grounding Conductors A separate bare or insulated copper conductor can be installed in or along the tray.

It should be bonded to each or alternate tray section using grounding clamps to maintain electrical continuity and mechanical stability under fault conditions. Insulated conductors are preferred in aluminum trays to prevent electrolytic corrosion. Bonding Between Tray Sections Each tray section must be electrically continuous.

Bonding clamps or connectors ensure that fault currents can flow safely across joints, maintaining a low-impedance path to ground.

Installation Considerations

Conductor Placement: Grounding conductors should run parallel to the cables in the tray and be connected at both ends to the grounding system. Material Selection: Use tin- or zinc-plated connectors for bonding, especially in moist environments, to prevent corrosion. Separation of Cables: Power and data/control cables should be separated to minimize electromagnetic interference (EMI) while maintaining grounding integrity.

Compliance: All installations must adhere to NEC standards, including tray fill limits, cable types, and grounding requirements.

Summary

Proper grounding of cables in cable trays enhances safety, reduces interference, and ensures regulatory compliance. Depending on the installation, either the tray itself can act as the EGC, or dedicated grounding conductors can be used, with careful bonding and material selection to maintain electrical continuity and prevent corrosion.

Following NE

C guidelines and best practices ensures a reliable and safe electrical system.