This article assesses the management tools of electric systems in developing countries. To promote the nuclear energy as an alternative resource in developing countries, the International Atomic Energy Agency (I.A.E.A.) has encouraged the development of a decision-making tool which optimizes operational activities in electric systems. Since 1982, most developing countries use that tool or a derivative one; recurrent management difficulties are encountered despite the numerous studies and the efforts to enhance the management performances. Activities are the main levers in the management of electric systems. They are set to improve the performances which translate the efficiencies. In dealing with the difficulties, none of the previous studies has considered the tool assessment. Monte Carlo or probabilistic or derating simulation methods are used in the tool Implementation; simulations are only relevant if models are realistic and the systems properly analysed. We show in this paper indirectly from the WASP notebook guide A (I.A.E.A.) 1984 and directly from the evolution of electrical system’s characteristics that the electric systems models are not suitable in developing countries. An unrealistic model stands for a system significantly different from the actual one; the differences lead to reference quantity value management difficulties and to the impossibility to set up the infinitesimal evolution responsible for the overall behaviour of the system and underlies the implementation of the tool. The article puts the constraints and associated activities at the centre of electrical system management, it opens prospects for efficiency management with a significant impact on upcoming electric systems.