Does UL List light curtains that are used on industrial machinery to prevent personal injury?

Question: Light curtains on industrial machinery

Does UL List light curtains that are used on industrial machinery to prevent personal injury?


Yes, light curtains are Listed under the category Active Opto-Electronic Protective Devices (NIPF), located on Page 60 of the 2002 General Information for Electrical Equipment Directory (White Book).

In January 2002 UL published new standards for Electro-Sensitive Protective Equipment, UL/ ANSI 61496-1 and 61496-2. UL 61496-1 contains general requirements and tests for all Electro-Sensitive Protective Equipment; UL 61496-2 contains specific requirements for Active Opto-Electronic Protective Devices, otherwise known as light curtains.

Light curtains are commonly used in industrial settings for the safeguarding of machinery that presents risk of personal injury. Light curtains typically consist of an emitter/ receiver pair. The length of the light curtain, number of light beams and spacing of light beams may vary depending upon customer application. When one or more beams of light are broken, due to for instance a hand in a point of hazard zone, within milliseconds a signal is sent to shut down machine operation. Signal redundancy and continuous selfchecking are among the requirements for light curtains.

In addition to an evaluation for fire and electric shock hazards, light curtains undergo a stringent investigation of their safety-related performance features. This includes evaluations of software reliability, Failure Mode and Effect Analysis (FMEA), EMC immunity, and resistance to mechanical and environmental stresses.

 Question: USE and USE-2

Are Type USE and USE-2 suitable for exposure to sunlight?


All UL Listed service entrance cables are required to be sunlight resistant as part of their UL Listing. Both the cable assembly and the individual inner conductors are sunlight resistant, and neither is required to be marked. This information is noted in the UL Guide Information for Service Entrance Cable (TYLZ) located on page 104 of the 2002 White Book.

As a side note, individual insulated conductors, such as THWN, that are not part of a service entrance cable assembly are not sunlight resistant, unless so marked, (i.e., “sunlight resistant”).


 Question: Electric sign

Does each individual part of an electric sign require a “Section ____ of _____” marking?


A UL Listed sign may be shipped in sections only when the sections form a complete sign and complete instructions for field assembly are provided. Each major subassembly is required to bear an electric sign section marking.

For example, separate channel letters and remote neon power supplies are considered major subassemblies and each subassembly requires a section marking. Sign faces, trim and mounting hardware are not considered major subassemblies.

The “section” UL Label has changed. The UL Guide information was revised to require each section to bear an “Electric Sign Section” Listing Mark in lieu of the “Section _____ of _____” marking where each section of the sign was assigned a number. The Electric Sign “Section _____ of ______” Listing Mark is still acceptable until the stock is depleted.

Electric signs are Listed under the category, “Signs” (UXYT). The UL Guide Information can be found on page 105 of the 2002 White Book or visit the UL Online Certification Database


 Question: Shower lights

Are lights installed in showers required to have GFCIs?


UL Listed luminaries are evaluated for compliance with the Standard for Luminaires, UL 1598. The UL Standard does not require integral GFCI protection for luminaries. If the manufacturer’s installation instructions require GFCI protection in the installation, then Section 110.3(B) of the NEC would be applicable. Also note that for some special occupancies in Chapter 5, the NEC requires GFCI protection to be provided for the equipment in the installation. The UL Guide Information for luminaires (IETX) can be found on page 40 of the 2002 General Information for Electrical Equipment Directory (White Book).

It is important to note that combination ceiling-insert exhaust fan/lights are Listed under the product category Electric Fans (GPWV) and are required by the Standard for Electric Fans, UL 507, to be marked, “Acceptable for use over a bathtub or shower when installed in a GFCI protected branch circuit.” This information is detailed in the Guide Information for this category located on page 203 of the 2002 White Book. In this case, the UL Standard does not require integral GFCI protection in the product. However, the product must be marked to indicate that a GFCI protected branch circuit should be used to supply power to the product. Section 110.3(B) of the NEC is applicable.


 Question: Listing mark on outlet box

Why isn’t the UL Listing Mark always required on an outlet box? I’ve seen the Mark on packaging, but once it’s discarded, it is difficult to verify Listing.


For some products, the UL Mark is on the smallest unit container. This is due to the size and/or shape of the products, which physically does not allow the UL Mark on the product itself. For outlet boxes, the UL Listing Mark is required on the product, or the UL symbol can be marked on the product and the complete Listing Mark of Underwriters Laboratories Inc. is marked on the smallest unit container. This practice has been in place for many years. This information is detailed in the UL Guide information for “Metallic Outlet Boxes” (QCIT) located on page 81 of the 2002 General Information for Electrical Equipment Directory (White Book).

For all UL Listed or Classified products, the Guide Information for each product category contains a description of how the product is to be marked to identify that the product is UL Listed or Classified under that product category.

About UL Solutions
UL Solutions helps create a better world by applying science to solve safety, security and sustainability challenges. We empower trust by enabling the safe adoption of innovative new products and technologies. Everyone at UL shares a passion to make the world a safer place. All of our work, from independent research and standards development, to testing and certification, to providing analytical and digital solutions, helps improve global well-being. Businesses, industries, governments, regulatory authorities and the public put their trust in us so they can make smarter decisions. To learn more, visit