Active filters are being increasingly considered as a viable alternative to passive filters for meeting harmonic distortion limits. The three phase configuration based on a voltage source configuration is the most widely proposed topology. However its application is restricted to balanced systems, hence it may not be suitable for industrial and commercial applications, in which power is distributed through a four wire system. One alternative is the use of half-bridge converters. This paper investigates the performance of the conventional three wire and the alternative four wire active filter configurations in the presence of load and line unbalance conditions