What's the difference between single-phase and three-phase rack PDUs?

The phases of a PDU, such as a single-phase PDU  or a three-phase PDU, describe the number of electrical phases that a PDU receives and transmits. Three-phase power is used by large power consumers, such as colocation data centers and hospitals, because that is the most efficient way to transport the large volumes of electricity required for those facilities. Single-phase power is used by smaller power consumers, such as small and medium businesses, schools and most office buildings.