The authors define the power components under sinusoidal and unbalanced conditions in three-phase, 4-wires circuits proposed as: dissymmetry power S-, and asymmetry power S 0 as components of total unbalanced power S unbalanced due to negative and zero currents components. The physical meaning of the power losses in unbalanced regimes is based on the losses on the neutral wire and on the increased losses in phase conductors due to unbalanced loads compared to balanced situation. A practical and simple algorithm, allowing calculating all specific variables of the unbalanced conditions as well as the power losses is also presented together with the results of a real case study.