This is the Chinese basic safety standard for insulation coordination in low voltage equipment, and its influence is indirect but pervasive: it is referenced by a very large number of Chinese product standards rather than being applied by manufacturers directly, so that the clearances, creepage distances and rated impulse voltages in a Chinese product standard are ultimately derived from this document. For a manufacturer entering the Chinese market the practical consequence appears during design review, when the clearance and creepage distances required by a Chinese standard are compared with those of the corresponding international standard for the same product and are occasionally found to differ because of a difference in the assumed overvoltage category or pollution degree. The standard adopts the international method without national deviation in the technical content, so the rules themselves are familiar; the difficulty lies in applying them to the environment assumed by the Chinese product standard concerned.