The mandatory national standard for gapless metal oxide surge arresters was issued as a compulsory document under the GB prefix, which in the Chinese system means that compliance was obligatory rather than voluntary, and it was the version referenced in the technical specifications used by the transmission and distribution utilities. There is no equivalent compulsory route in the international system: the international standard of the same subject is a voluntary reference that a purchaser may or may not cite, whereas the GB designation at the time of issue carried legal force for products within its scope. The standard has since been reissued as a recommended national standard and the compulsory designation has lapsed, so procurement documents in China now show both numbers, and a supplier preparing a bid has to establish which of the two a specification refers to. Utility type approval in China is granted against the current edition, and the same standard is cited in arrester selection for substations at every voltage level.