How many meters of electrical cable tray should be grounded
Metallic cable trays must be grounded at regular intervals: every 15 meters for power cables and every 20 meters for data cables.
Grounding Intervals
For power cable trays, metallic trays should be connected to the earthing (grounding) network every 15 meters to ensure safety and proper fault current handling . For data cable trays, the recommended maximum distance between grounding points is 20 meters to maintain electrical continuity and reduce electromagnetic interference (EMI), . These intervals help protect personnel and equipment from electrical faults and ensure compliance with EMC standards.
NEC Compliance
According to NEC Article 392 and Article 250.96, all metallic cable trays must be grounded regardless of whether they are used as an equipment grounding conductor (EGC), . Grounding can be achieved in three ways:
- Installing a separate EGC conductor in or on the tray.
- Using multi-conductor cables with individual EGCs.
- Using the cable tray itself as the EGC if it meets the minimum metal area requirements specified in NEC Table 392.60(A), .
Best Practices
- Ensure mechanical and electrical continuity between tray sections using grounding clamps or bonding connectors .
- Avoid placing bare copper conductors in aluminum trays to prevent electrolytic corrosion; use insulated conductors with exposed bonding points instead .
- Powder-coated trays are not conductive and should only be used for data cabling systems .
- Verify that the tray's cross-sectional area is sufficient if it is intended to serve as the EGC, especially for circuits with high ground-fault protection ratings .
Summary
To maintain safety and compliance:
- Power cable trays: ground every 15 meters.
- Data cable trays: ground every 20 meters.
- Use proper bonding methods and ensure continuity across all tray sections.
- Follow NEC Article 392 and 250.96 for grounding and bonding requirements.
- Consider material compatibility and insulation to prevent corrosion and maintain long-term reliability .
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