Does the cable tray need dual-point grounding

Two-point grounding of a cable tray involves connecting the tray to the grounding system at two separate locations to ensure electrical continuity and safety under fault conditions.

Purpose of Two-

Point GroundingTwo-point grounding is used to enhance the reliability of the grounding path for metallic cable trays. By connecting the tray at two points to the building grounding system, it ensures that: Fault currents have a low-resistance path to earth, allowing protective devices like breakers or fuses to operate quickly. Electrical continuity is maintained even if one connection becomes loose or corroded.

The risk of shock hazards, equipment damage, or fire is minimized in industrial or commercial installations.

Implementation Guidelines

Connection Points: Typically, the cable tray is bonded at the start and end of the tray run or at alternate sections if the tray is very long. Each connection should be mechanically secure and electrically continuous. Bonding Methods: Use grounding clamps or bonding jumpers to connect the tray to the main grounding conductor.

Ensure that all splice points and fittings maintain conductive continuity. Mechanical connections alone may not guarantee electrical continuity, so bonding jumpers are recommended. Equipment Grounding Conductor (EGC): The tray itself can serve as the EGC if it meets NEC requirements, but a separate EGC can also be installed in or on the tray and bonded to the tray sections.

For aluminum trays, use insulated conductors to prevent electrolytic corrosion, removing insulation only at bonding points with tin- or zinc-plated connectors. Compliance with NEC: NEC Article 392 requires metallic trays to be electrically continuous and properly bonded. Two-point grounding aligns with NEC guidance to ensure the tray can safely conduct fault currents and facilitate the operation of overcurrent protective devices.

Additional Considerations

Tray Material: Steel and aluminum trays have different current-carrying limitations for grounding purposes. Ensure the tray material is suitable for the expected fault current. Length of Tray Runs: For long runs, additional grounding points may be necessary to maintain low impedance.

Environmental Factors: Moist or corrosive environments may require insulated or plated conductors to maintain long-term reliability. Key Takeaway: Two-point grounding of cable trays is a best practice for safety and NEC compliance, providing a reliable path for fault currents, reducing shock hazards, and ensuring the proper operation of protective devices in electrical installations.