IEC 60909-3 Ed. 2.0 b:2003, Short-circuit currents in three-phase a.c. systems - Part 3: Currents during two separate simultaneous line-to-earth short ... short-circuit currents flowing through earth

specifies procedures for calculation of the prospective short-circuit currents with an unbalanced short circuit in high-voltage three-phase AC systems operating at nominal frequency 50 Hz or 60 Hz, i.e.