Harmonic currents generated by personal computers and their effects on the distribution system neutral current

The switching mode power supplies used in personal computers are major sources of harmonic currents. Measured and calculated waveforms and harmonic levels of input currents of various types of personal computers are presented. Harmonics of odd order are present in the input currents of personal computers. The magnitudes of the harmonic currents up to the eleventh harmonic are significant. The harmonic currents of two or more simultaneous PC loads of the same type add in phase. The third, the fifth, and the seventh order harmonics in different types of personal computers strongly reinforce one another. Large third-harmonic currents (up to 87% of the fundamental) are present in all kinds of computers. These currents generate neutral currents that are as high as 1.7 times the life current. Recommendations are made on preventing potential problems.<>