The distribution agents of electrical energy have a commitment with the end customers to comply with certain reliability indices in order to guarantee the quality of the service they provide, among these, one of the most important is to maintain continuity in the electrical supply. This article presents a methodology with a possible application to real electrical distribution systems for calculating the level of unserved energy through the use of the concepts of operational zones and unavailability, through the analysis of failures in each of the different lines. and subsequent outages that occur in the test system. Different scenarios and configurations are evaluated by varying the position of reclosers and fuses in order to present the results and the corresponding conclusions.