Specifies the requirements for insulation fault location systems which localize insulation faults in any part of the system in unearthed IT a.c. systems and unearthed IT a.c. systems with galvanically d.c. circuits having nominal voltages up to 1000 V a.c., as well as in unearthed IT d.c. systems with voltages up to 1500 V d.c., independent of the measuring principle. This part is to be used in conjunction with IEC 61557-1.