Grounding Method for Low-Voltage Cables in Cable Trays

Low-voltage cables in cable trays are grounded using equipment grounding conductors (EGC) or the tray itself, with single-point, two-point, or cross-bonding methods to ensure safety and minimize electromagnetic interference.

Key Grounding Principles

Equipment Grounding Conductor (EGC) OptionsEGC in the cable tray: A separate insulated conductor runs along the tray, bonded to each tray section using grounding clamps to maintain electrical continuity and mechanical stability under fault currents.

Individual EG

C in each cable: Each multi-conductor cable includes its own EGC, which can be connected to the tray or system ground. Cable tray as EGC: In qualifying facilities, the metallic tray itself can serve as the EGC if it meets minimum cross-sectional area requirements and is electrically continuous.

Bonding and Continuity

All metallic tray sections are bonded together through bolts, splice plates, or clamps to ensure electrical continuity. Side rails of ladder or trough trays are bonded to the next section, and bonding jumpers are used where gaps exist. Aluminum trays require insulated conductors to prevent electrolytic corrosion when bonded with copper EGCs.

Grounding MethodsSingle-Point Grounding: The cable screen or armor is grounded at one end only, minimizing circulating currents and induced voltages along the cable length.

Two-

Point (Both-Ends) Grounding: Both ends of the cable are grounded, with a parallel grounding conductor to equalize potential differences. This method is simple and economical but may allow circulating currents, which can cause heating.

Split or Cross-

Bonding: Sections of cable screens are cross-connected to reduce induced voltages and circulating currents, especially for longer cable runs. Conceptual Diagram DescriptionCodeCopy[Power Source / Ground Bus] │ │ ┌─────────────┐ │ Cable Tray │─────────┐ │ Section 1 │ │ └─────────────┘ │ │ │ ┌─────────────┐ │ │ Cable Tray │ │ │ Section 2 │─────────┘ └─────────────┘ │ [Equipment / Load] EGC Placement: A separate insulated conductor runs along the tray, bonded to each tray section with grounding clamps. Tray as EGC: If the tray is used as the EGC, bonding jumpers connect side rails across sections.

Single-

Point Grounding: Only one end of the EGC or tray is connected to the main ground.

Two-

Point Grounding: Both ends of the EGC or tray are connected to the ground bus.

Cross-

Bonding: Sections of the cable armor or screen are interconnected in a crosswise manner to cancel induced voltages. Additional ConsiderationsEMC and Noise Protection: For low-voltage signal or communication cables, grounding also reduces electromagnetic interference. Shielded trays or solid-bottom trays with covers can provide additional EMI/RFI protection.

Material Selection: Steel is effective for shielding up to ~100 kHz, while aluminum or copper is better at higher frequencies. Safety Compliance: All grounding practices should comply with NEC Article 250, NEMA VE-2, and TIA/EIA 607 for telecommunications circuits. This approach ensures electrical safety, fault current management, and EMC protection for low-voltage cables in cable trays.