This International Standard specifies the method for determining the dielectric breakdown voltage of insulating liquids at power frequency. The test portion, contained in a specified apparatus, is subjected to an increasing a.c. electrical field by means of a constant rate of voltage rise until breakdown occurs.

The method applies to all types of insulating liquids of nominal viscosity up to 350 mm²s^–1 at 40 °C. It is appropriate both for acceptance testing on unused liquids at the time of their delivery and for establishing the condition of samples taken in monitoring and maintenance of equipment.