The US Nationally Recognized Testing Laboratories (NRTLs) and Canadian Accredited Certification Organizations (ACOs) are third-party private organizations certified by OSHA (Occupational Safety and Health Administration) and the SCC (Standards Council of Canada) respectively. They perform safety evaluation and certification of products to be used in North America.

Products are required to conform to the UL standards for the US and the CSA standards for Canada, and the certified products are eligible to bear the mark of the certification body. Those that are compliant with both UL and CSA standards are marked with adjacent indicators “C” and “US” on either side. UL and CSA are given as the representative certification bodies, but whichever certification body grants the certification, the certification itself is considered to be equivalent.