Abstract: A method for determining the resistive component of the leakage current impedance (Ri50) of a downstream branch to an alternating current network having a live phase (L), a neutral conductor (N), and a protective conductor (PE) conducted by: (a) measuring a differential current ILN between the live phase (L) and the neutral conductor (N); (b) measuring a voltage U between the live phase (L) and the neutral conductor (N) or between the live phase (L) and the protective conductor (PE); (c) correcting a phase shift between the differential current ILN and the voltage U; (d) determining several individual differential current values ILN,i and several individual voltage values Ui, the differential current values ILN,i being phase-corrected with respect to the voltage values Ui; (e) determining the effective power P from the several individual differential current values ILN,I and the several individual voltage values Ui; (f) determining the effective voltage UEff by the voltage values Ui; and (g) determining the r