Underwriter’s Laboratories (UL) evaluates performance of a single aspect of wire mesh basket cable tray according to the 2011 UL White Book:

This category covers cable trays intended for assembly in the field and for use in accordance with Article 392 of 2011 ANSI/NFPA 70, “National Electrical Code” (NEC). They have been Classified as to their suitability for use as equipment grounding conductors in accordance with Sections 392.3(C) and 392.7(B) of the NEC. The cable trays are marked on the outer surface of the sidewall of the tray indicating the cross-sectional area of the grounding metal.

According to 2011 NEC 392.60(A), cable tray must be marked to show the area of metal in the tray.

In addition to performance as an Equipment Grounding Conductor, NFPA 70 - the 2011 National Electric Code (NEC) defines the physical properties of cable tray: 2011 NEC 392.100 Construction Specifications:

(A) Strength and Rigidity. Cable trays shall have suitable strength and rigidity to provide a equate support for all contained wiring.
(B) Smooth Edges. Cable trays shall not have sharp edges, burrs, or projections that could damage the insulation or jackets of the wiring.
(C) Corrosion Protection. Cable tray systems shall be corrosion resistant. If made of ferrous material, the system shall be protected from corrosion as required by 300.6.
(D) Side Rails. Cable trays shall have side rails or equivalent structural members.
(E) Fittings. Cable trays shall include fittings or other suitable means for changes in direction and elevation of runs.
© Copyright 2011 National Electrical Code

When a tray is field modified to create a turn or junction, the installer cuts sections of metal from the tray in Diagram A, then uses a splice-washer or other mechanism to patch the tray back together in the desired configuration as shown in Diagram B below.

"When a UL-Listed product is modified after it leaves the factory, UL is unable to determine if the product continues to comply with the safety requirements used to certify the product without investigating the modified product." (source:www.ul.com)

Since a cable tray’s eletrical performance depends on the cross-sectional area, or the amount of metal in the tray, removal of metal sections reduces this cross-section and may degrade performance. Although is an 18” wide tray, the modifications has resulted in a cross section of only .11 sq inches. If a tray was rated at .20 sq inches cross-section and the installer reduces that to .11 sq inches, what will happen to the fault current looking for a return path to the over-current protection device?

Additionally, for products which are cULus Classified, the UL classified load performance may be severely reduced by such modifiacations.

Why Take A Chance? Field modification of wire mesh basket tray may result in incorrectly labeled product as well as potentially hazardous installations where there is insufficient metal cross-section to perform as an Equipment Grounding Conductor under 2011 NEC 392.60(A).

PRO-10™ prefabricated fittings connected to PRO-10™ straight sections maintains 100% UL™ Classification and fully complies with NEC 392 and is the safest solution.


“Field modification would void the approvals.”
-Steve Koschwitz, Chief Inspector, Seminole County Building Division, FLorida

“NEC 392.5(E) which is currently adopted by the State of Florida … specifically calls for fittings to change direction…392.5 (A), (B), (C), (D), (are) also affected by field modifications and would not be acceptable.”

– Victor Lombardi, Acting Electrical Director
Miami-Dade County Building Department

“Chapter 56, “Dallas Electrical Code” requires electrical equipment to be listed and labeled. If a piece of equipment is altered in the field we require it to be recertified by a NRTL with proper documentation supplied to the chief’s office and field inspector.”
– Lawrence Heckler, Chief Electrical Inspector, City of Dallas

“You are correct in advising customers that your UL Classification is voided by their modification of your product. DCRA will only accept products that are used per the manufacturer’s guidelines that resulted from being tested and labeled for the specific applications by UL or similarly recognized testing agencies. Any change to a product requires a re-testing and re-labeling for the new use or application.”
– Sydney Lester, Manager, Permits Operations Division,
Department of Consumer & Regulatory Affairs (DCRA), Washington, D.C.

UL only examines cross sectional for US classification, for Canadian Classification, UL also tests load capacity and finish performances. Wiremaid strongly recommends cULus classification to ensure load performances.