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This part of International Standard IEC 71 applies to three-phase a.c. systems having a highest voltage for equipment above 1 kV. It specifies the procedure for the selection of the standard withstand voltages for the phase-to-earth, phase-to-phase and longitudinal insulation of the equipment and the installations of these systems. It also gives the lists of the standardized values from which the standard withstand voltages shall be selected.

This part recommends that the selected withstand voltages should be associated with the highest voltage for equipment. This association is for insulation co-ordination purposes only. The requirements for human safety are not covered by this Standard.

Although the principles of this part also apply to transmission line insulation, the values of the withstand voltages may be different from the standard withstand voltages.

The apparatus committees are responsible for specifying the withstand voltages and the test procedures suitable for the relevant equipment taking into consideration the recommendations of this Standard.

NOTE - In IEC 71-2 Application Guide, (under revision), all rules for insulation co-ordination given in this Standard are justified in detail, in particular the association of the standard withstand voltages with the highest voltage for equipment. When more than one set of standard withstand voltages is associated with the same highest voltage for equipment, guidance is provided for the selection of the most suitable set.