___ is/are generally the producers of harmonics on electrical systems.

• A. Resistive heating loads
• B. Non-linear loads
• C. Incandescent lighting loads
• D. Household cooking equipment

Answer: (B)

Harmonics arise when current is drawn in a non-proportional, non-sinusoidal way. Linear loads—where current follows voltage in a steady, proportional manner—keep the current waveform close to a pure sine wave, so little harmonic content is produced. Non-linear loads, however, draw current in sharp bursts or in a non-sine shape due to their internal electronics (like rectifiers, switching power supplies, electronic ballasts, or VFDs). Those pulsed currents contain multiple frequency components that are integers of the fundamental frequency, creating harmonic currents and distortion on the system. Because of that, non-linear loads are the primary sources of harmonics. Resistive heating and incandescent lighting are generally linear and don’t introduce significant harmonics, and household cooking equipment is typically resistive as well, so they don’t contribute much to harmonic generation.