Total harmonic distortion (THD)
THD measures how far a generator’s AC output deviates from a pure sine wave, as a percentage. Under 5% THD is generally considered safe for sensitive electronics; conventional open-frame generators can exceed 15–25%, while inverter generators typically stay under 3%.
Distorted power stresses switch-mode power supplies, motor controls, and microprocessor-based appliances — modern furnaces, variable-speed pumps, and audio equipment are common casualties of dirty generator power.
Manufacturers of conventional generators rarely publish THD figures; “clean power” marketing without a number is not a specification. If electronics matter, an inverter generator (or a published sub-5% THD figure) is the safe choice.