The value that electric companies assign to the reliability of their electric power supply is a key factor for efficient decision making, since it is a permanent task they face both in their operations and planning activities. This value depends on variables that are not easily observable; for this reason, the calculation of these costs strictly require the application of methodologies mainly built on proxy estimations with which the economic and the social impact can be reasonably inferred, when segments of users face an outage or interruption of public electric supply service. This impact, expressed in monetary terms, is known as the Cost of Energy Not Supplied (CENS). Besides establishing proxy variables to obtain CENS, the proposed methodology is applied to estimate the impact of programmed interruptions occurrence on the Ecuadorian electric system, on the basis of the Gross Domestic Product by productive sector and on the evaluation of the level of preparation of those sectors. The CENS values found are applied to Ecuador in planning research of the electric sector both on mid and long-range terms.