The design of the protection system becomes fundamental to guarantee the adequate operation of the electric system under fault conditions, as it makes possible to isolate only faulted devices without affecting to the other ones. Electric fuses are protection devices broadly used in distribution networks, being designed to interrupt the current by means of the melting of one of their components when excessive currents flow through it during a period of time. In this paper the thermal analysis of a medium voltage fuse by means of the finite element method is presented. The fuse model has been designed and simulated under different conditions of ambient temperature with Cosmos software tool. The results obtained from the simulation are compared with those obtained from real tests.