Three-phase electric power is a common method of alternating-current electric power transmission, and is commonly used to power large motors and other large loads.

Three-phase has properties that make it very desirable in electric systems. The phase currents tend to cancel one another, summing to zero in the case of a linear balanced load. Power transfer into a linear balanced load is constant, which helps reduce vibrations. Three-phase can produce a magnetic field that rotates in a specified direction, which simplifies the design of electric motors.