Phases of a UPS, such as a single-phase UPS or a three-phase UPS, describe the number of electrical phases that a UPS receives and transmits.
Electrical utilities generate three-phase power because that is the most efficient way to transport electricity over long distances. And for larger power consumers, such as large data centers, industrial manufacturing and hospitals, the power stays as three-phase, requiring a three-phase UPS. For smaller power consumers, including residential or office buildings and most schools, the power is converted to single-phase power.
Some applications contain a mix of single-phase and three-phase equipment and require a UPS that can protect both.