A method for detecting and localizing faults in a medium voltage, MV, and low voltage, LV, distribution grid (3, 4) comprising a plurality of MV and LV nodes and a plurality of MV and LV branches, as well as several MV/LV transformers each arranged to connect one MV node with one LV node, the MV and LV distribution grid further being provided with a monitoring infrastructure comprising metering devices assigned to particular LV nodes of the distribution grid, each of one of said metering devices being arranged to measure a nodal voltage of the LV node to which it is assigned and a current flowing into or out of said LV node through an upstream branch incident on said LV node, each one of said particular LV nodes preferably being one of the nodes that a MV/LV transformer is arranged to connect with a MV node, the monitoring infrastructure further comprising a central processing unit and a communication means arranged for allowing communication between the metering devices and the central processing unit; wherein the method comprises the following steps: I. have the metering device at each one of said particular LV nodes, measure the voltage v(t) and the current i(t) with a sampling rate that is high enough for sampling said voltage and said current over a bandwidth with an upper limit of at least 1 kHz. II. have the metering device at each one of said particular LV nodes use the voltages and the currents measured in step I to calculate, for each one of a succession of evaluation time windows, the mean value of the nodal negative-sequence voltage, V neg, and further calculate a variation of the calculated mean value with respect to the previous evaluation time window, III. have the metering device at each one of said particular LV nodes, asses the following first criterion for each one of the evaluation time windows except the first one: "the variation of the mean value of the nodal negative-sequence voltage, V neg-rltv, calculated in step II is larger than a first given threshold", if the assessment comes out positive for a particular evaluation time window, have the metering device send a fault notification comprising the calculated variation for the particular evaluation time window to the central processing unit. IV. have the central processing unit use fault notifications received during a predefined time lag window from metering devices assigned to different LV nodes, to identify the fault location with the help of grid topology information. I. have the metering device at each one of said particular LV nodes, measure the voltage v(t) and the current i(t) with a sampling rate that is high enough for sampling said voltage and said current over a bandwidth with an upper limit of at least 1 kHz. II. have the metering device at each one of said particular LV nodes use the voltages and the currents measured in step I to calculate, for each one of a succession of evaluation time windows, the mean value of the nodal negative-sequence voltage, V neg, and further calculate a variation of the calculated mean value with respect to the previous evaluation time window, III. have the metering device at each one of said particular LV nodes, asses the following first criterion for each one of the evaluation time windows except the first one: "the variation of the mean value of the nodal negative-sequence voltage, V neg-rltv, calculated in step II is larger than a first given threshold", if the assessment comes out positive for a particular evaluation time window, have the metering device send a fault notification comprising the calculated variation for the particular evaluation time window to the central processing unit. IV. have the central processing unit use fault notifications received during a predefined time lag window from metering devices assigned to different LV nodes, to identify the fault location with the help of grid topology information.