Proper Grounding of Cable Trays Essential for Electrical Safety

Those unassuming cable trays suspended from factory ceilings or data center rafters play a far more crucial role than their modest appearance suggests. As the backbone of power distribution systems, their proper bonding and grounding can mean the difference between safe operation and catastrophic failure.

Cable trays serve as the structural framework supporting electrical, control, and communication cables throughout facilities. Available in ladder-type, channel-type, and wire mesh configurations, these systems function as power distribution highways. Wire mesh trays have gained particular popularity due to superior ventilation and installation flexibility.

Two fundamental concepts govern cable tray safety: bonding and grounding. Bonding ensures continuous electrical connectivity between tray sections, while grounding establishes a low-impedance path to earth for fault currents.

The National Electrical Code (NEC) mandates that metal cable trays must be bonded to safely conduct potential fault currents. NEC 392.7(A) specifies that metal cable trays supporting electrical conductors must be bonded per conductor enclosure requirements, with additional guidance in NEC 250.96 and Article 250 Part IV.

Effective bonding creates an uninterrupted pathway for fault currents to reach grounding points. UL-listed bonding components should connect tray sections at each termination point and at 50-65 foot intervals to building steel structures. Common attachment methods include beam clamps, threaded rods, and hangers.

When trays mount to non-conductive surfaces like concrete, supplemental bonding jumpers or continuous grounding conductors must bridge these intervals. Steel's higher electrical resistance necessitates this frequent bonding to maintain low-impedance paths.

Grounding connects cable trays to earth, providing a safe discharge path for fault currents that would otherwise endanger personnel and equipment. NEC 392.7 outlines four strict requirements when using cable trays as Equipment Grounding Conductors (EGC):

• All tray components must be clearly identified as EGC
• Minimum cross-sectional areas must meet Table 392.7(B) requirements
• Permanent markings must display metal cross-sections
• Components must be bonded per NEC 250.96 using listed connectors or properly sized jumpers

Notably, cable trays serve as EGC in less than 1% of installations, primarily in specialized industrial applications like refineries.

Myth 1: Field modifications void UL listings. In reality, 99% of tray applications only require bonding (not EGC function), making most field modifications acceptable when using UL-listed bonding hardware.

Myth 2: UL-listed connectors make all field modifications acceptable. While true for bonding applications, EGC applications require supplemental grounding conductors when modifying tray cross-sections.

• Enhanced equipment protection from lightning and transient currents
• Improved personnel safety through reliable fault current paths
• Reduced electromagnetic interference and noise

As critical infrastructure components, cable trays demand careful attention to bonding and grounding details. Proper implementation following NEC requirements and manufacturer specifications ensures safe, reliable power distribution while protecting both equipment and personnel.