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Should grounding wires be installed in cable trays

ODN and passive infrastructure knowledge brief Published 13 Aug 2023

Prepared for preliminary research by the GESTIONVAL ODN knowledge desk. Confirm network topology, split ratio, box or cabinet capacity, joint closure rating and loss budget against current standards and product documentation.

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 installing a separate grounding wire.Purpose of Grounding Cable Trays

Grounding cable trays provides a safe path for stray electrical currents to flow into the earth, reducing the risk of electric shock, equipment damage, and fire hazards. It also stabilizes the electrical system and helps clear fault currents efficiently, ensuring protective devices operate correctly .

Methods of Grounding
  1. Using the Cable Tray as the EGC Metal trays can serve as the equipment grounding conductor if they meet NEC cross-sectional area requirements. Steel trays are suitable for circuits with ground-fault protection up to 600 amperes, while aluminum trays can handle up to 2,000 amperes. The tray must be electrically continuous, and bonding connections should be made at joints using tin- or zinc-plated connectors .
  2. Full-Length Grounding Conductor A continuous insulated grounding wire can be run along the length of the tray. This wire is bonded to each tray section using grounding clamps, providing a reliable path for fault currents and mechanically securing the conductor to prevent displacement under magnetic forces .
  3. Parallel EGCs For multi-circuit trays, a single conductor can serve as a common EGC for all circuits, or individual EGCs can be paralleled with the tray to ensure low impedance and safety compliance .
Material Considerations
  • Copper Wire: Excellent conductivity and corrosion resistance, ideal for most installations.
  • Hot-Dip Galvanized Steel: Durable and corrosion-resistant, cost-effective.
  • Stainless Steel: Suitable for harsh or corrosive environments . Note: Bare copper should not be used in aluminum trays due to the risk of electrolytic corrosion; insulated conductors are preferred, with insulation removed only at bonding points .
Installation Guidelines
  • Ensure all metallic trays are grounded according to NEC Article 250.96, even if the tray is not used as an EGC .
  • Maintain electrical continuity across tray sections using bonding clamps or connectors.
  • Keep grounding conductors clear of flammable materials and corrosive environments.
  • Verify grounding resistance is low (ideally 4 ohms or less) to ensure effective fault current diversion .
  • For wire mesh trays supporting cables with built-in EGCs, a separate grounding wire is usually not required, but the tray should have a low-impedance path to a non-system ground .
Summary

Proper grounding of cable trays is essential for safety and system reliability. Depending on the installation, either the tray itself or a separate grounding conductor can be used, with careful attention to material selection, bonding, and NEC compliance. Following these practices ensures that fault currents are safely conducted to ground, protecting both personnel and equipment .

Should grounding wires be installed in cable trays - GESTIONVAL ODN INFRASTRUCTURE S.L. [PDF]

Should grounding wires be installed in cable trays

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Technical note

This reference is intended for preliminary ODN and passive infrastructure research. Topology, split ratio, box or cabinet capacity, closure rating, cable type, test limits and applicable standards must be verified for the specific project.

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