Established with sponsorship by an organization of fire underwriters in 1894, in the wake of a major fire at the Chicago World’s Fair in 1893, UL is a non-profit testing laboratory and the standards body most recognized in the U.S. It examines and tests devices, systems and materials to determine their relation to hazards to life and property, and publishes standards and certifications. Although UL certification is basically optional, a great many electrical products made in the U.S. obtain UL certification.

UL standards aim to remove risks of fire and electric shock caused by electric products. Products in the U.S. generally require certification by a Nationally Recognized Testing Laboratory (NRTL).

UL standards relate to six technical sectors: (1) electrical engineering; (2) fire prevention; (3) anti-theft and alarms; (4) heating and air conditioning; (5) injuries and chemical injuries; and (6) shipping engineering. SMC’s products fall under electrical engineering.

UL standards certification includes listing certification and recognition certification. Listing certification is generally of an end product, while recognition certification is for parts included within a product. SMC’s valves and switches are basically considered parts to be incorporated into a product, and are subject to recognition certification. UL-certified products are assigned a CCN (Category Control Number) according to the product category. A CCN, in principle, consists of four letters and a one-digit number.

The United States and Canada have a Mutual Recognition Agreement (MRA) providing for the recognition of certifications by the other. When a product is certified by UL based on Canadian standards (CSA standards), the certification mark for the said product will be the C-UL mark shown below, meaning conformity to CSA standards. *The above certification marks are examples used UL (being an NRTL). Marks used by other NRTL’s are different.