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.).

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