This part of IEC 61643 applies to surge isolation transformers (SITs) dedicated to surge mitigation and for connection to 50/60 Hz power circuits and equipment rated up to 1 000V rms. This document covers the surge and mitigation performance of SITs with an impulse withstand voltage performance at least 30 kV, and provides standard methods for testing and rating. This document covers surge-related parameters but does not address typical transformer tests and parameters covered by the IEC 61558 series. This document also does not cover SIT operation under differential mode lightning surge conditions.