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Is it permitted to replace a sign face on a listed sign?

Posted By Underwriters Laboratories, Tuesday, March 01, 2005
Updated: Saturday, February 16, 2013

Question: Sign faces

Is it permitted to replace a sign face on a listed sign?


Depending on the sign design and the location of the sign, either dry or wet location, a sign face may provide many functions. In some cases the sign face may provide a weather shield, in other cases it may also provide the electrical enclosure for the sign. In either case the sign face material is required to have specific properties that must be verified if that sign is going to maintain its UL Listing.

Replacing the sign face on a listed sign is essentially considered a field modification of a listed sign. When a UL listed product is modified after it leaves the factory, UL has no way to determine if the product continues to comply with the safety requirements used to certify the product without investigating the modified product.

UL can neither indicate that such modifications "void” the UL Mark, nor that the product continues to meet UL’s safety requirements, unless the field modifications have been specifically investigated by UL under a field evaluation or field inspection. A field evaluation or field inspection can be initiated by calling 1 (877) ULHelps (854-3577). More information on field evaluations can be also obtained online at

UL has an official policy on field modification of listed products that can be found on the Regulator page at:

 Question: ULtimate email and TCA

What are ULtimate Email and TCA: Electrical Connections?


ULtimate Email is a complimentary email notification system initiated by UL’s Regulatory Services Department early last year. AHJs, contractors and all interested parties can register, select their interest areas and receive email notifications when information develops that is of interest to them.

TCA: Electrical Connections (or TCA: EC) is an acronym forCode Authority®: Electrical Connections.

TCA: Electrical Connections is a new electronic newsletter published by the Regulatory Services Department.

This bulletin features news and technical information targeted specifically at issues of interest to the electrical inspection community. Released eight times a year between the quarterly issues of Code Authority newsletter, this publication will provide timely updates from the world’s leader in electrical safety and product certification. If you would like to sign up for electronic distribution of this publication or for ULtimate Email, visit the Regulators page on UL’s web site Click on the "ULtimate Email Subscribe Today!” box on the right side of the page to register for ULtimate Email and subscribe to TCA: Electrical Connections. Register today so that you will always be the first to know.

 Question: Neon lighting and ground-fault protection

Do all listed neon lighting power supplies meet the secondary ground-fault protection requirements in Section 600.23(B) in the NEC? Are they required to have a test button? If not, how can I indentify them?


Neon lighting power supplies and transformers are listed under the product category of Neon Transformers and Power Supplies (PWIK) located on page 83 of the 2004 UL General Information for Electrical Equipment Directory (the White Book). These devices have been evaluated for compliance with the Standard for Neon Transformers and Power Supplies, UL 2161. These transformers and power supplies have also been evaluated for the secondary ground-fault protection requirements in the Section 600.23 of the NEC.

Neon transformers and power supplies are not required by UL 2161 to be provided with a test or bypass button for the secondary of these devices. A test or bypass button is an option some manufacturers incorporate into their design. Transformers and power supplies listed under this category are identified by the UL Listing Mark and the product name "Neon Transformer” or "Neon Power Supply.”

The Guide Information for PWIK as well as Listings under this category can also be located at UL’s Online Certification Directory, just log onto, click search by Category Code /Guide Information and enter PWIK, then click search.

 Question: Type NM cable

I have seen several Type NM, nonmetallic-sheathed cables going through a single clamp into an outlet box or panelboard enclosure. Is this okay?


Type NM cable clamps are Listed under the product category Nonmetallic-Sheathed Cable Connectors (PXJV) located on page 84 in the 2004 UL White Book. Per the Guide Information on that page, except for duplex connectors or where otherwise marked on the carton to indicate connecting of more than one cable, the connectors covered under this category have been investigated for connecting one cable only.

The Guide Information for PXJV as well as listings under this category can also be located at UL’s Online Certification Directory, just log onto, click search by Category Code / Guide Information and enter PXJV, then click search.

Tags:  March-April 2005  UL Question Corner 

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