CPUC Tariff Rule 21

Third parties must use certified equipment (both behind the meter and on the distribution grid) when attempting to interconnect new components to the grid. Certified equipment is equipment that has passed through rigorous certification testing procedures done by Nationally Recognized Testing Laboratories (NRTLs); UL is one such example. NRTLs create testing procedures for equipment that verify equipment functionality and safety to pre-set testing standards created by nationally recognized engineering groups such as IEEE.