Natural canceling of current harmonics in office loads and its effect upon the transmission capacity of distribution cables

Office loads and especially computer-type ones, draw significant zero-sequence harmonic currents, which in a TN-S type network, add up in the neutral conductor. In this paper, measurements have shown that fluorescent lighting loads that employ magnetic ballasts draw a 3^rd harmonic current that is almost in opposition with the 3^rd harmonic current drawn by a computer. This leads to a natural reduction of the 3^rd harmonic current in the neutral conductor when mixing these load types and thus to an increase of the transmission capacity of low-voltage power cables. This increase is also verified mathematically by a significant increase of the ampacity derating factor of these cables when they feed mixed computer and fluorescent lighting loads.