In this thesis, the Croatian standard HRN EN 60909-3 is described in detail, and examples of calculations in the NEPLAN program are given in accordance with the used standard. The HRN EN 60909-3 standard describes the procedures for the calculation of currents during two separate simultaneous line-to-earth short circuits in isolated neutral or resonant earthed neutral systems, as well as the calculation of partial currents through earth in case of a single line-toearth short circuit in solidly earthed or low-impedance earthed neutral systems. In the second chapter, the currently valid Croatian standards HRN EN 60909 are listed. The definitions of quantities used for the purposes of this standard are described and the corresponding formulas are given. The third chapter describes the initial symmetrical short circuit current, peak short circuit current, symmetrical short circuit breaking current and steady-state short circuit current. The distribution of the currents during two separate simultaneous line to earth short circuits is described and the corresponding examples are given. The fourth chapter describes partial short circuit currents flowing through earth in the case of the line-to-earth short circuit inside a station, outside a station and in the vicinity of a station. The calculation of the reduction factor for overhead lines with earth wires is also described. The fifth chapter describes the calculation of the reduction factor and current distribution in the case of cables with metallic sheath (shield) earthed at both ends. The case of a three-core cable and three single-core cables was considered. In the sixth chapter, the NEPLAN program is described, which was used for three examples of single-phase short circuits. An examples of the calculation of partial currents through earth in the case of line-to-earth short circuit in a station, as well as the calculation of the reduction factor and current distribution in the case of line-to-earth short circuit in a station powered by a three-core cable are also presented, taken from the HRN EN 60909-3 standard.