This paper presents a detailed power flow solution approach to apply to the energy loss evaluation for branch circuits or feeders of a dwelling unit or building to examine the suitability of the usual loss factor approach. The time-to-time and season-to-season changes in active and reactive power consumptions for each appliance are considered. Considering that daily load curves are quite different for weekdays and holidays, and also different for different seasons, sixteen daily load curves are created to represent the daily consumption characteristics for each kind of appliance, eight for daily active and another eight for reactive power consumption. The detailed power flow solution approach has resulted in the explicit energy loss evaluations for branch circuits or feeders of a dwelling unit or building and their corresponding determination of the daily, weekly, monthly and annual system electrical parameters. The results mentioned above are then used as a benchmark to discuss the suitability of the loss factor approach for evaluating the energy loss of branch circuits or feeders of a dwelling unit or building. (C) 2012 Elsevier B.V. All rights reserved.