This standard applies to hollow insulators made of ceramic material, with their fixing devices, intended for use with a permanent gas pressure greater than 0,5 bar having an internal volume equal to or greater than 1 litre (1000 cm3). They are intended for use in electrical equipment operating on alternating current with a rated voltage greater than 1000 V and a frequency not greater than 100 Hz or for use in direct current equipment with a rated voltage greater than 1500 V. The hollow insulators covered by this standard consist of hollow insulator bodies, open from end to end, with or without sheds. Note 1: the gas can be: dry air, inert gases, e.g. sulphur hexafluoride or nitrogen or a mixture of such gases. Note 2: the hollow insulators are intended for use in electrical equipment, for example: circuit-breakers, switch-disconnectors, disconnectors, earthing switches, instrument transformers, surge arresters, bushings, cable sealing ends. This standard supplements, and modifies if necessary HD 329 (IEC 233) which applies to the body of hollow insulators