Calculation of ampacities and sizing of line and neutral conductors in the presence of harmonics

Abstract

Today nonlinear loads are becoming a bigger part of the electrical load in industrial and commercial power systems. Nonlinear loads generate harmonics in line currents resulting in additional conductor heating. This heating results in a higher temperature rise of the cable which can exceed the rated temperature of the cable if it is not sized to carry harmonic currents. Existing ampacity tables by the NEC or IEEE are based on heating generated by sinusoidal currents. The presence of nonsinusoidal harmonic currents in the cable requires derating of the cable. This paper has developed an equation for calculating the ampacity for line and neutral conductors in the presence of harmonics