With the proliferation of nonlinear loads such as personal computer in an educational building, high neutral harmonic currents have been observed. High neutral currents in three-phase four ire distribution power systems can cause tots of harmonic problems such as overloaded neutral conductors and malfunction of protective equipment. On-site measurements of harmonic currents and voltages were made and the corresponding equivalent circuits was developed. The circuit model under study was simulated numerically and graphically through the use of the software MATLAB. Simulation results verifying the effect of a single-tuned passive filter for the neutral harmonic current reduction are presented.