This paper focuses on the optimization problem of the maintenance function. For this purpose, the optimization of the maintenance of the power distribution systems must be based on a reliable and robust model and should be started as soon as preliminary design information is available. The FMECA method is a living document that is not only beneficial when used during the design phase but also during system use. As more information on the system is available the analysis should be updated in order to provide the most benefit. The FMECA study aims to reduce downtime and improve equipment reliability since the design. This allows to optimize the components while identifying the most critical elements and helping decision makers to define maintenance plan appropriate maintenance policy. In the end to prove the interest of the FMECA study in maintenance optimization by reliability, a case study was performed on the equipments for the benefit of society SONELGAZ in Algeria.