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A general probabilistic model is presented of an electrical system node capable of unifying supply reliability (SR) and voltage quality (VQ) from the point of view of a sensitive user. It is a discrete state model based on the classification characteristics of measurement results, as recommended by the SR/VQ standards. It makes it possible to take into account: 1) the user's sensitivity, simply by drawing border lines between the states whose effects cause malfunctions and the other states, and 2) the uncertainty related to the random nature of the phenomena involved and of the equipment sensitivities. The authors use the Markov process theory to develop and solve the model, taking advantage of the so-called device of stages extension to represent the nonexponential nature of voltage dip durations and the recovery times consequent to long and short interruptions. In order to demonstrate the usefulness of the proposed model and the importance of the recovery time probability distribution, a representative case study is also discussed.