This standard provides some guidance on the selection of the electric strength of equipment, of surge diverters or protective gaps, and of the most suitable degree of switching overvoltage control.NOTE: There is no Australian standard for the protective characteristics of protective gaps.It is based on apparatus types and ratings in use at the present time. As new equipment and equipment characteristics are developed and proved, this standard should not be interpreted as limiting their adoption. This standard covers both phase-to-earth and phase-to-phase insulation, and it deals separately with the following three voltage ranges of the highest voltage for equipment:(a) Range A: above 1 kV to less than 52 kV.(b) Range B: from 52 kV to less than 300 kV. (c) Range C: 300 kV and above.It covers installations of all kinds and in all situations involving voltages higher than 1 kV, whether they are exposed to lightning or not, with the exception of overhead lines. However, the test procedures apply also to the latter.