This International Standard is applicable to post insulators of organic material for indoor service in electrical installations or equipment operating in air at atmospheric pressure on alternating current with a nominal voltage greater than 1 000 V up to, but not including, 300 kV, as defined by range I of IEC 60071-1, and a frequency not greater than 100 Hz. Composite insulators are not covered by this standard. The object of this standard is – to define the terms used; – to define electrical and mechanical characteristics of post insulators of organic material and to prescribe the conditions under which the specified values of these characteristics are verified; – to prescribe methods of testing; – to prescribe acceptance criteria. This standard does not give numerical values for insulator characteristics; nor does it deal with a choice of insulators for specific operating conditions. IEC 60273 specifies numerical values for electrical and mechanical characteristics and gives the dimensions necessary for interchangeability of post insulators.