How many meters of cable tray require a grounding cable

All metallic cable trays require grounding along their entire length; there is no specific meter threshold—continuous grounding is mandatory for safety and NEC compliance.NEC Guidelines

According to NEC Article 392, all metallic cable trays must be grounded and bonded to ensure electrical safety, even if the tray is not used as an equipment grounding conductor (EGC) itself . This applies to every section of the tray, regardless of its length, because any discontinuity in grounding can create shock hazards, equipment damage, or fire risks .

Methods of Grounding

1. Tray as EGC: If the metallic tray meets the cross-sectional area requirements in NEC Table 392.60(A), it can serve as the EGC. This requires that all tray sections, fittings, and splices maintain electrical continuity .
2. Separate Grounding Conductor: If the tray does not qualify as an EGC, a separate grounding conductor (minimum #4 AWG) must be installed along the tray, either inside or attached to it .
3. Bonding Jumpers: At splice points or mechanical connections that may not ensure continuity, bonding jumpers are required to maintain a continuous conductive path .

Practical Considerations

• Material Compatibility: Use bimetallic washers when connecting copper grounding conductors to aluminum trays to prevent galvanic corrosion .
• Wire Mesh Trays: Ensure all sections are electrically continuous and properly bonded, as coatings can reduce conductivity at connection points .
• Safety: Continuous grounding ensures that any fault current has a low-resistance path to the building grounding electrode system, allowing protective devices to trip quickly .

Summary

There is no minimum length of cable tray that exempts it from grounding. Every metallic tray installation, whether a few meters or hundreds of meters, must be grounded continuously, either by the tray itself (if it meets NEC requirements) or by a separate grounding conductor, with proper bonding at all connections to maintain electrical continuity and safety .