Bonding and Grounding Wire Mesh Cable Tray

Understanding UL Classification and Field Modifications

This document addresses claims that field modifications to wire mesh cable tray, such as creating bends and turns, can void its UL Classification. UL's definition of "field modified" could literally mean any cut to tray. However, standard practice for over 40 years involves field modifications.

The key distinction lies in whether the tray is intended for bonding or grounding as the Equipment Grounding Conductor (EGC).

Bonding vs. Grounding

Bonding (Approximately 99% of Installations):

• Ensures electrical continuity and the capacity to safely conduct fault current.
• Governed by NEC 392.7(A) and Article 250.96.
• Requires UL Classified Splices for connecting tray sections.
• Does not require the tray to act as the EGC.
• Applies to Data or Multi-conductor Cable Tray applications.

Grounding (Approximately 1% of Installations):

• The tray serves as the EGC.
• Governed by NEC 392.7(B).
• Requires specific UL identification, compliance with cross-sectional area requirements (Table 392.7(B)), durable marking, and bonding per 250.96/250.102.
• Typically used in applications like refineries and large industrial areas.

Illustrative Scenarios:

• Data Cables: Tray bonded per NEC 250.96 with UL splices. No EGC required.
• Multi-conductor Power: Tray bonded per NEC 250.96 with UL splices. EGC is inside the conductor per UL.
• Single Conductor Power: Tray bonded with a continuous ground wire on the side, sized per the maximum breaker.

UL's Position on Field Modifications:

According to Underwriters Laboratories, Inc., cable tray assemblies are investigated for bonding between sections using manufacturer-provided hardware. If positive mechanical grounding connections are not provided, assemblies are intended to be bonded with installer-provided mechanical connectors or bonding jumpers, in accordance with NEC 392.7(B)(4). For UL certification details, visit www.ul.com/database and search for "cable tray assemblies".

Field modifications, such as using UL Classified Pre-formed fittings or splicing sections with UL Classified Splices, do not void UL classification as long as bonding is maintained.

For more information, download the white paper "The facts on field modification of UL Classified wire mesh cable tray" by Fred Hartwell and the Wire Mesh Technical Guide from www.legrand.us/cablofil.

For inquiries, contact Legrand/Cablofil at 1-800-658-4641.

Benefits of Bonding and Grounding

• Reduces Noise and EMC: Removes electro-static potential and induced magnetic currents.
• Increases Equipment Safety: Mitigates lightning currents and transient currents.
• Improves Personal Safety: Reduces potential fault currents by providing a low impedance path to trip breakers.

Legrand/Cablofil Accessories for Bonding and Grounding

Legrand/Cablofil wire mesh cable tray and its range of splices are tested and comply with CSA, IEC, NEC, NEMA, and UL requirements for low resistance, ensuring excellent electrical continuity and grounding for safe installations.

UL Classified Splices:

• EDRN Fast Splice
• EDT Splice Plate
• ED 275 Universal Splice Bar
• SWK Splice Washer Kit
• RADT 90 Kit Radius Tee Kit

Grounding Accessories:

• GNDSB Grounding Lug for AWG 4-14 ground wire
• GNDCL Grounding Lug for AWG 1/0-6 ground wire