Applies to hollow insulators made of ceramic material, with their fixing devices, intended for use with a permanent gas pressure greater than 50 kPa gauge having an internal volume equal to or greater than 1 l (1 000 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 1 500 V.