Underwriter Laboratories (UL) is a U.S. product safety certification organization that has been testing products and developing safety standards for more than a century.
Underwriters Laboratories tests approximately 20,000 products, components and materials over the course of a year. It is a global organization made up of many companies and testing facilities. Products and printed circuit boards tested by Underwriters Laboritories are given a UL designation. There are different levels of marking: Level A evaluates general design complexity, Level B evaluates standard design complexity, and Level C evaluates high design complexity.