The power quality industry has become increasingly concerned about harmonics. As the use of power electronics increases, so too does the level of voltage distortion appearing on power systems. Some single-phase loads, like the ubiquitous PC, are relatively low-wattage devices, but have high harmonic content. In commercial offices, computers and their peripherals are used in such large quantities that the neutral current is often greater than the phase current. Higher wattage devices like heat pumps and central air-conditioning with variable speed drives have only worsened the problem of harmonic distortion. However, the higher wattage nonlinear loads have yet to appear in any great quantity.