The on-line detection of the faults in low-voltage (LV) distribution networks has become possible by the implementation of the smart meters (SM's). Due to technical and economical reasons SM's will not be installed in each household. For an efficient and accurate fault identification it is necessary to determine the optimal ratio of SM's in relation to the number of consumers. This is achieved by using the Fuzzy method. In this paper, the influence of the number of SM's on the accuracy of the fault identification is presented.