IEC/TR 60725:2012, which is a technical report, records the information that was available and the factors that were taken into account in arriving at the reference impedances that were incorporated in IEC 60555 and which are now incorporated in some parts of IEC 61000-3. In addition, information is given on the impedances of public supply networks associated with service current capacities =100 A per phase. The third edition includes brings two mainly significant technical changes with respect to the previous edition:
- a new survey and other data from countries with public supply networks operating at 60 Hz have been included; and
- recommendations that were applicable to 50 Hz systems are now mirrored by new recommendations that are relevant to 60 Hz systems.