The fourth harmonic is an AC waveform component that oscillates at exactly four times the frequency of the foundational fundamental wave. In standard electrical power grids operating at 60 Hertz, the fourth harmonic frequency registers at 240 Hertz. As an even-order harmonic, it typically appears in single-phase or unbalanced non-linear loads, rectifiers, and specialized magnetic circuits where waveform symmetry is disrupted. While even-order harmonics like the fourth are less prevalent in balanced three-phase utility systems compared to odd-order harmonics, their presence still contributes to overall Total Harmonic Distortion, requiring proper filtering and waveform analysis to prevent component stress.