Modifications Affect UL Listing

Question: Listed product modification

Can a UL Listed product be modified in the field if the manufacturer indicates that the revision is ok and sends out new parts?


The UL Mark applies to products as they were originally manufactured. UL does not know the effect modifications in the field will have on a product. Therefore, unless the modifications are specifically tested and evaluated by UL, UL cannot say that the modifications void the UL Mark, or that the product continues to comply with UL’s safety
requirements. The exception would be when the product has specific replacement markings.

Question: Listed product

How can I confirm if a product is UL Listed?


Only products that bear the UL Listing Mark are considered UL Listed. If you would like to verify a Listing, UL offers direct access to search UL’s Online Certification Directory Database A search can be conducted by using a number of parameters using the information provided on the UL Mark and the product nameplate. This search may include the UL file number, product identity, the manufacturer’s name and the model number of the product.

You may also be able to verify the Listing by referencing the published UL directories. If you do not have access to the internet or UL’s printed directories, you can contact a UL
Regulatory Services Representative.

Question: Harmonized UL standards

Currently there are approximately 93 bi-national or IEC harmonized UL standards. Since European and other countries have different utility service voltages and frequencies, how has harmonization affected the safety relating to installation and use of equipment?


UL Standards for Safety are developed to be compatible with the National Electrical Code (NEC®) installation requirements. Harmonized UL Standards maintain this compatibility. Standards that have been harmonized with IEC documents include appendices addressing specific installation requirements for various countries.

Question: Safety smarkings

Does UL require manufacturers to place required safety markings in a readily visible location on electrical equipment, such as air-conditioning units, electric signs, and luminaires?


UL Standards for Safety require safety markings to be located in a readily visible location after installation. Tools are not to be required to disassemble the product to view the safety markings. In addition, the UL Listing Mark is to be located such that it is visible without the use of a tool.

For some products, such as wire connectors, the UL Mark is on the smallest unit container. This is due to the size or shape of the product, which physically would not permit the UL Mark on the product itself.

Question: Installation instructions

Are the installation instructions part of the UL Listing? Are all Listed products required to have installation instructions? Are installation instructions reviewed by UL?


Installation instructions are considered to be a part of the UL Listing.

The UL Standards for Safety used to investigate products contain specific requirements regarding the content and appearance of the instructions. Installation instructions are not required to be marked with the UL Mark, but they are required to be provided with the product bearing the UL Mark. Some products are not required to have installation instructions when the National Electrical Code contains all the necessary installation requirements, such as outlet boxes. UL staff reviews the instructions, both during the initial evaluation of the product, as well as during the continual Follow-Up Service at the factories. The clarity of the instructions is also reviewed.

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