The optimal power rating of a series active filter is important not only in design of compensator for a specific application, but also in determining the best compensation strategy for a specific application. This paper focus mainly on the confront of the power rating of a combined system consisting of two small rating series active filters and a shunt passive filter generally designed for balanced condition, and the power rating required when it's working under unbalanced conditions. This paper highlights the overload imposed to the active series filters for two different degree of imbalance showing that even if the overloaded doesn't exist the system wont be free of harmonic pollution, exceeding the IEEE 519 recommendations