scope:

This publication provides some guidance on the selection of the electric strength of equipment, of surge arresters or protective spark gaps, and on the extent to which it will be useful to control switching overvoltages. The object of this publication is not to give strict rules for insulation co-ordination and design, but to provide guidance toward rational and economical solutions. Therefore it is intended to consider only a few basic cases in this publication, it being evident that installations constituting exceptions to normal design, or included within systems having exceptional characteristics, will require special study by experienced engineers. It covers installations of all kind and in all situations involving voltages higher than 1 kV, whether or not they are exposed to lightning, with the exception of overhead lines. However, the test procedures apply also the latter.