Manufacturers explain that modifications were made to meet specific customer requirements, or for some unknown reason, the UL Mark or markings were not applied at the factory. What is UL’s position on


Frequently, we are finding that more manufacturers are making field modifications to their equipment after it leaves the factory. Some examples include changing a short-circuit current rating label on a switchboard from 42K to 65K; or, changing equipment markings from “Suitable Only For Use As Service Equipment,” to “Suitable For Use As Service Equipment.” Manufacturers explain that modifications were made to meet specific customer requirements, or for some unknown reason, the UL Mark or markings were not applied at the factory. What is UL’s position on this practice?



UL requires markings to be on UL Listed and Classified products constructed under UL’s Follow-Up Services (FUS) Program before they leave the factory. If a product is altered or a label is added after it leaves the factory, there is no way that UL can discern whether the product still complies with UL requirements without an evaluation. In such cases, UL conducts a Field Inspection.

Field Inspection Service is appropriate for products that do not bear the UL Mark, and for Listed products that have been altered after they have left the factory, but for which representative samples have been investigated by UL. If these samples meet UL’s requirements, the product may be eligible to bear a UL Mark. A UL representative visits the equipment site and examines these products to determine whether they conform to the applicable UL Follow-Up Services Procedure. This Procedure contains the requirements used by UL when conducting FUS visits at production facilities. If a Field Inspection confirms that a product is indeed eligible to bear a UL Mark, only then can the manufacturer or its designated representative apply the authorized UL Mark to the product – under the supervision of the UL Field Representative.

Since only a manufacturer can request this service, regulatory authorities are urged to encourage manufacturers to initiate a UL Field Inspection. The appropriate regulatory authority is notified before the UL Field Representative goes to the site and is advised of the inspection results. AHJs have the option of witnessing the inspection, and may also request a UL Letter Report that provides the technical requirements for the equipment, to assist AHJs in their decisions on acceptance of modified products. However, UL cannot provide a Letter Report determining that modified products comply with the Listing requirements without first conducting a Field Inspection.

The only exception for field modifications authorized by UL is when the product has specific replacement markings. For example, a switchboard may have specific grounding kits added in the field. The switchboard is marked with a list of specific kit numbers that have been evaluated by UL for use with that particular switchboard. Only the grounding kits indicated on the product’s marking have been evaluated by UL for use with that product.

All markings required by UL do not need be included on the Listing Mark label, nor is the UL Listing Mark the only marking required to appear on the product. One way to determine which markings may be required (and those markings that are optional) is to review the Guide Information for the appropriate product category in the 1999 edition of the General Information for Electrical Equipment Directory – also known as the “UL White Book” – or the appropriate UL Product Directory. The Guide Information for each category, as well as general information included in the front section of the UL product directories, provides important information for products covered under each specific category, ranging from the scope of Listing to important markings and installation requirements.

UL also publishes seven free marking guides specifically for AHJs that also specify which markings are to be included on a product. These guides cover products from lighting fixtures and switchboards to swimming pool and spa equipment, which can be ordered online by directly accessing the UL web site If you do not have access to the Internet, contact Danica Walker in Northbrook, Ill., by phone at (847) 272-8800, ext. 43731; by fax at (847) 509-6235; or by e-mail

UL’s position on Field Modifications to Listed and Classified products are also included on page 279 of the 1999 White Book, under the heading Field Engineering Services. You can also contact UL Regulatory Services toll free, between 8 a.m. and 4 p.m., local time, at the UL office nearest you:

• 1-800-595-9841 (Southeastern)

• 1-800-595-9842 (Eastern)

• 1-800-595-9843 (West)

• 1-800-595-9844 (Midwest)

• 1-800-595-9845 (Pacific Northwest)

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