This paper presents an economic assessment of a fault location method designed for medium voltage (MV) distribution grids leveraging distributed additional voltage measurements on some secondary substations. The aim is to provide a distribution system operator (DSO) with the optimal number of additional voltage measurement devices to make a fault location method (FLM) that has been developed in previous work as profitable as possible. Indeed, this optimal placement algorithm for this FLM provides a priority order for additional measurement location. However, the profitability of installing additional measurements derives from the gain in reliability that it achieves. This paper proposes an algorithm to optimally find the number and location of both remotecontrolled switches (RCSs) and manual switches (MSs) of distribution networks based on reliability indiceswith objective values fixed by the regulator. Then, the optimal number of additional measurements, which can be phasor measurement units (PMUs) for instance, is presented. The method has been tested on some realistic feeders reconstructed from Enedis's open database.