Single or three-phase power?

Three-phase power, the most efficient way to distribute power over long distances, allows for large industrial equipment to operate more efficiently. It’s characterized by three single-phase waves that are offset in their phase angle by 120 degrees, or one-third of the sine wave period as illustrated in Figure 1.

Three-phase voltage can be measured from each phase to neutral or from one phase to any other. The voltage relation between phase-to-neutral and phase-to-phase is a factor of the square root of three (e.g., 120V versus 208V).

Conversely, single-phase power is distributed through common household outlets to power everyday equipment such as laptops, lighting and televisions. When looking at an oscilloscope image of the voltage coming out of a single-phase outlet as illustrated in Figure 2, there’s only a single wave. Single-phase power is obtained by simply using only one phase of a three-phase system. Its root mean square (RMS) voltage is 120V (for North America) and it oscillates between its peaks of ±170V at 60 Hz (or 60 times a second).

Single-phase or three-phase power?

Single-phase advantages Three-phase advantages
The standard for locations where three-phase power is unavailable. Can help balance the loads on the utility power of the building.
Usually easier to distribute power in low kVA and low-density applications. Usually easier to distribute power in higher kVA and high density rack applications.
Allows for smaller amperage electrical devices within the solution (breakers, wiring, panels, etc.).

Interested in more information like this?
download your free UPS handbook