THDi refers to a byproduct of UPS operation. Efficiency refers to how well the UPS converts input power into output power (and the amount of power the UPS consumes in order to operate). The higher the efficiency, the more the UPS system will save in operation costs. 220/380 V models are up to 97% efficient in ECO mode (up to 94% in normal mode) — several percentage points higher than some competitive models. The 120/208 V and 277/480 V models are up to 96% efficient in ECO mode (up to 93% in normal mode) — several percentage points higher than some competitive models.

