Nationally Recognized Testing Laboratory (NRTL)

A Nationally Recognized Testing Laboratory (NRTL) is an independent organization accredited by the Occupational Safety and Health Administration (OSHA) to test and certify that electrical products meet established safety standards. UL (Underwriters Laboratories) is the most well-known NRTL, but there are others.

The NEC requires that all electrical equipment used in solar installations — including panels, inverters, racking, combiner boxes, and disconnects — be listed by an NRTL. This ensures that every component has been independently tested for electrical safety, fire resistance, and durability. Besides UL, other NRTLs that certify solar equipment include: CSA Group (Canadian Standards Association), TÜV Rheinland, TÜV SUD, Intertek (ETL mark), and MET Laboratories. Products certified by any OSHA-recognized NRTL are equally acceptable under the NEC — a panel with a TÜV certification is just as valid as one with a UL mark. When reviewing solar equipment, look for an NRTL listing mark on the product label and verify the certification is current. Inspectors check for NRTL listings during the permitting and inspection process.