This paper considers the problem of estimating the power breakdowns for the main appliances inside a building using a small number of power meters and the knowledge of the ON/OFF states of individual appliances. First we solve the breakdown estimation problem within a tree configuration using a single power meter and the knowledge of ON/OFF states and use the solution to derive an estimation quality metric. Using this metric, we then propose an algorithm for optimally placing additional power meters to increase the estimation certainty for individual appliances to the required level. The proposed solution is evaluated using real measurements, numerical simulations and by constructing a scaled down proof-of-concept prototype using binary sensors. Categories and Subject Descriptors H.4 [Information Systems Applications]: Miscellaneous General Terms Algorithms,Design, Experimentation, Measurement, Performance, Theory Keywords Energy breakdowns, Electric Load Estimation, Electricity Consu...