IEC 60781:1989

This application guide presents a practical method to be used when calculating short-circuit currents in low-voltage networks. The method corresponds strictly with IEC 60909 and leads to conservative results with sufficient accuracy.
Two short-circuit currents which differ in magnitude are to be calculated:
-the maximum short-circuit current which causes the maximum thermal and electromagnetic effects on electrical equipment and determines the required capacity or rating;
-the minimum short-circuit current which may be a basis for the adjustment of protective devices.