This standard applies to switching impulse tests, when specified, on insulators as defined in Clause 6 and intended for use on a.c. installations with highest voltage 300 kV, and above.
Notes 1 — This standard is not intended to be applied to polluted insulators. A switching impulse test on polluted insulators is considered to be premature at the present state of the art 2 — The lower limit of 300 kV maybe modified. as a consequence of possible modifications in IEC Publication 71, Insulation Co-ordination