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The UL Mark
Underwriters Laboratories® Inc. (UL) is an independent product safety certification organization. Based in Northbrook, Illinoismarker, UL develops standards and test procedures for products, materials, components, assemblies, tools and equipment, chiefly dealing with product safety. UL also evaluates and certifies the efficiency of a company’s business processes through its management system registration programs. Additionally, UL analyzes drinking and other clean water samples through its drinking water laboratory in South Bend, Indianamarker.

UL is one of several companies approved for such testing by the U.S. federal agency OSHA. OSHA maintains a list of approved testing laboratories, known as Nationally Recognized Testing Laboratories.

About UL

UL Recognized Component Mark
UL does not “approve” products. Rather it evaluates products, components, materials and systems for compliance to specific requirements, and permits acceptable products to carry a UL certification mark, as long as they remain compliant with the standards. UL offers several categories of certification. Products under its listing service are said to be “UL Listed,” identified by the distinctive UL mark. In some cases, a component may be “UL Recognized,” meaning UL has found it acceptable for use in a complete UL Listed product. Other products may be “UL Classified” for specific hazards or properties. UL maintains a directory of more than 3 million products through a publicly available, online database.

A manufacturer of a UL-certified product must demonstrate compliance with the appropriate safety requirements, many of which are developed by UL. A manufacturer must also demonstrate that it has a program in place to ensure that each copy of the product complies with the appropriate requirements. UL conducts periodic, unannounced follow-up inspections at manufacturers’ locations to check ongoing compliance. If a product design is modified, a representative example may need to be retested before a UL mark can be attached to the new product or its packaging.

UL has developed more than a thousand Standards for Safety, many of which are American National Standards, and evaluates nearly 20,000 types of products. A typical standard for electronic products includes not only requirements for electrical safety, but also spread of fire and mechanical hazards. UL evaluates products for compliance with specific safety requirements. UL certification does not guarantee the product will perform acceptably or that it is safe under all conditions (such as product misuse). UL develops its Standards to correlate with the requirements of model installation codes, such as the National Electrical Code.

The UL Mark does not carry any legal weight beyond that of any other trademark. In this sense, it is different from the CE Marking or the FCC Part 15 requirements for electronic devices, which are required by law. In practice, however, it may be extremely difficult to sell certain types of products without a UL Mark. Large distributors may be unwilling to carry a product without UL certification, and the use of noncertified equipment may invalidate insurance coverage. It is common practice in many fields to specify UL Listed equipment or UL Recognized materials. Local jurisdictional authorities, such as building, electrical and fire inspectors, may be reluctant to accept a product for installation in a building unless it carries a recognized third-party compliance mark such as the UL Mark.

In the past 20 years, great strides have been made in harmonizing international safety standards. For example, manufacturers can obtain certification to both U.S. and Canadian national standards through a single UL certification process. The label for products certified for both Canada and the United States includes “C” and “US” outside of the UL logo.

The European analog of the UL Mark is the CE Marking. The CE Marking indicates that a product complies with the essential requirements of the applicable European laws or directives regarding safety, health, environment and consumer protection. Manufacturers generally self-declare compliance with these requirements, whereas the UL Mark requires independent certification from UL. A product that bears a CE Marking may also bear a certification mark such as the UL Mark.


UL headquarters
Underwriters Laboratories Inc. was founded in 1894 by William H. Merrill. At the beginning of his career at age 25 as an electrical engineer in Boston, Merrill was sent to investigate the Chicago World Fairmarker’s Palace of Electricity. Upon seeing a growing potential in his field, Merrill stayed in Chicago to found Underwriters Laboratories.

Merrill soon went to work developing standards, launching tests, designing equipment and uncovering hazards. Aside from his work at UL, Merrill served as the National Fire Protection Association’s secretary-treasurer (1903–1909) and president (1910–1912) and was an active member of the Chicago Board and Union Committee. In 1916, Merrill became UL’s first president.

UL published its first standard, “Tin Clad Fire Door,” in 1903. The following year, the UL Mark made its debut with the labeling of a fire extinguisher. In 1905, UL established a Label Service for certain product categories that require more frequent inspections. UL inspectors conducted the first factory inspections on labeled products at manufacturers’ facilities—a practice that remains a hallmark of UL’s testing and certification program.

UL has expanded into an organization with 66 laboratories and testing and certification facilities serving customers in 104 countries. It has also evolved from its roots in electrical and fire safety to address broader safety issues, such as hazardous substances, water quality and food safety.

UL Testing and Certification Operations to Go For-Profit

On August 28th 2007, the nonprofit and tax-exempt UL announced that its board of Trustees had resolved to develop a for-profit testing and certification subsidiary to allow for more agility in the increasingly competitive world wide testing and certification marketplace. The parent nonprofit company will continue to develop safety standards and the for-profit subsidiary is intended to generate money to be used for this safety work.
Melville, Long Island location

UL Standards

Electrical Enclosures

  • Boxes-Junction and Pull (BGUZ)
  • Cabinets and Cutout Boxes-Sheet Metal (CYIV)
  • Industrial Control Panel Enclosures (NITW).

Industrial Control Panels

  • Industrial Control Panels (NITW)
    • Power Press Control Panels

Industrial Control Equipment

  • Auxiliary Devices (NKCR)
  • Electromechanical
  • Solid State
  • Mechanical
  • Electronic
  • Combination Motor Controllers (NKJH)
  • Float and Pressure-Operated Switches (NKPZ)
  • Magnetic Motor Controllers (NLDX)
  • Manual Motor Controllers (NLRV)
  • Motor Controllers-Miscellaneous (NMFT)
  • Miscellaneous Apparatus (NMTR)
  • Switches, Industrial Control (NRNT)
  • Programmable Controllers (NRAQ)
  • Proximity Switches (NRKH)

High-Voltage Industrial Control Equipment

  • Motor Controllers, Over 1500 V (NJHU)
  • Motor Controller Accessories-Over 1500 V (NJIJ)
  • Medium Voltage Power Conversion Equipment (NJIC)

Power Conversion Equipment

  • Power Conversion Equipment (NMMS)

See also


  1. NEC 2005-110.3(B)
  2. UL Press Statement
  5. UL Standards
  6. Flame Control Panels

External links

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