Line Interactive UPS

In normal operation the load is fed from the mains through a tapped autotransformer (AVRGlossary · Power qualityAutomatic Voltage Regulator (AVR)A device that automatically maintains a constant voltage level to protect electrical equipment from fluctuations.). When the voltage drops or rises, the UPS changes tap and corrects it without drawing on the battery. It switches to the inverterGlossary · UPS technologyInverterThe component inside a UPS that converts DC power from batteries back to usable AC power. only when the voltage goes out of range or is lost, with a transfer time typically of a few milliseconds.

It is the most common choice for computers, small servers, network equipment and security systems, offering a good balance of cost and protection. A small line-interactive UPS at full load typically gives a few minutes of runtime, roughly 3–10, enough for a safe shutdown.

However, it does not isolate the load from waveform distortion or frequency changes the way an online UPS does. For critical or sensitive equipment, or for operation with a generator, consider an online double-conversion UPS.