Cable tray grounding requirements standards

Metallic cable trays must be grounded according to NEC Article 250 and 392, and can serve as equipment grounding conductors (EGC) under specific conditions.

NEC Requirements for Cable Tray Grounding

Metallic cable trays are required to be grounded regardless of whether they are used as an EGC. NEC Article 250.96 mandates that all metallic raceways, including cable trays, be grounded to ensure safety and prevent electrical shock hazards . When a cable tray is used as an EGC, it must meet the metal area requirements specified in NEC Table 392.60(A), which defines the minimum cross-sectional area of the tray side rails based on the circuit's fuse rating, breaker ampere rating, or ground-fault protection setting .

Using Cable Trays as Equipment Grounding Conductors

Cable trays can serve as the EGC in installations where qualified personnel maintain and service the system. When used as an EGC:

• The tray must be electrically continuous and bonded at joints using grounding clamps or connectors .
• Insulated conductors are recommended when using aluminum trays to prevent electrolytic corrosion, with insulation removed at bonding points .
• Steel trays should not be used as EGCs for circuits with ground-fault protection above 600 A, and aluminum trays should not exceed 2000 A .

Bonding Practices

Even if a separate EGC is installed in the tray, it is desirable to bond the conductor to each or alternate tray sections. This ensures mechanical stability under fault conditions and maintains a low-impedance path for fault currents . Proper bonding helps the protective devices operate quickly, reducing the risk of electrocution or fire.

Material Considerations

• Steel trays: Strong and durable, suitable for most industrial applications, but limited in high-current EGC applications .
• Aluminum trays: Lightweight and corrosion-resistant, but require insulated conductors to prevent galvanic corrosion when bonded with copper EGCs .
• Nonmetallic trays: Cannot serve as EGCs and require separate grounding conductors .

Summary of Best Practices

1. Ground all metallic cable trays per NEC Article 250.96.
2. Use the tray as an EGC only if it meets NEC area and continuity requirements.
3. Bond tray sections with grounding clamps for mechanical and electrical continuity.
4. Avoid bare copper in aluminum trays; use insulated conductors with proper bonding.
5. Ensure the tray's material and size are suitable for the circuit's fault current rating.
6. Maintain accessibility and proper clearances for inspection and maintenance . Following these standards ensures electrical safety, compliance with NEC, and reliable operation of cable tray systems in industrial, commercial, and data center environments.