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In electrical distribution systems, low current faults may be caused by a high impedance fault or by the fault current limitation caused by the neutral to ground connection. In the former case, an indirect contact or insulation degradation give a high value of the fault impedance. In the latter, the neutral grounding may be either isolated or compensated. Nevertheless, these types of faults do not produce enough current so that the traditional overcurrent relays or fuses are not able to detect the fault. This paper presents a new methodology, based on the superposition of voltage signals of certain frequency, for the detection of low current single phase faults in radial distribution systems. The simulation analysis and laboratory tests carried out have proved the validity of the methodology for any type of grounding method.