Abstract: A method is disclosed for blocking a switch which is upstream when viewed from an electrical supply, downstream of which is connected a switch, wherein the switching contacts of the switches open automatically when a current threshold value is exceeded. In order to achieve a rapid detection of a short circuit in the electrical network with little outlay, in at least one embodiment it is proposed that the current is sampled, digitalized, and wavelet coefficients of at least one segmentation level are in each case calculated for a fixed specified number of immediately successive digitalized current values via a wavelet transform and compared with a wavelet threshold, and that the blocking signal is sent to the upstream switch when a specified number of immediately successive wavelet coefficients exceeds the associated wavelet threshold value in each case.