Cable trays are equipped with continuous grounding conductors

Metallic cable trays can serve as continuous grounding conductors, but proper bonding and installation practices are essential to ensure electrical safety and NEC compliance.

Grounding Principles for Cable Trays

Cable trays are often used as Equipment Grounding Conductors (EGC), providing a low-impedance path for fault currents to protect personnel and equipment from electrical hazards. The tray itself can act as the EGC if it is electrically continuous and properly bonded at all joints and splice points. This ensures that any stray or fault current is safely directed to the facility's grounding system, reducing the risk of electric shock, fire, or equipment damage.

Continuous Grounding Requirements

Electrical Continuity: While cable trays do not need to be mechanically continuous, they must be electrically continuous. Bonding jumpers or grounding clamps are used where mechanical connections alone may not provide reliable conductivity. Material Considerations: Aluminum trays are excellent conductors but may require insulated EGCs to prevent electrolytic corrosion, especially in moist environments.

Steel trays are strong but less conductive, so proper sizing and bonding are critical.

U

L Classification: Trays intended to serve as EGCs should be UL-Classified, indicating suitability for grounding purposes and ensuring the metal thickness can handle fault currents without melting.

EG

C Options: In addition to using the tray itself, a separate bare or insulated copper conductor can be installed in or on the tray and bonded to each section. This is a desirable practice to enhance safety, even if not strictly required by the NEC.

Best Practices

Ensure all tray sections are mechanically tight and electrically bonded. Remove paint or coatings at bonding points to maintain conductivity. Avoid using bare copper in aluminum trays; use insulated conductors with proper bonding connections.

Size the grounding conductor according to the largest circuit breaker in the tray to handle potential fault currents safely.

Safety and Compliance

Properly grounded cable trays minimize shock hazards, fire risks, and electromagnetic interference (EMI). They also ensure compliance with NEC Article 392 and related sections, which govern cable tray grounding, bonding, and EGC requirements. Continuous grounding is critical for facilities where personnel may service the tray system, ensuring that fault currents are quickly cleared and the system remains safe.

In summary, metallic cable trays can function as continuous grounding conductors, but achieving effective grounding requires careful attention to bonding, material selection, and NEC-compliant installation practices.