The basic principles that drive three-phase electrical power were developed in the late 1800s by Nikola Tesla. Utilities can send this form of electricity great distances; industries use it to run motors efficiently.
Each of the three phases of industrial electric power is called alternating current (AC). Unlike direct current (DC), which has a fixed positive and negative polarity, alternating current changes polarity in the form of a smooth, regular sine wave.
Every phase of three-phase electrical power is alternating current. The three sine waves are locked to the same 60 Hertz (Hz) frequency, though the second phase lags the first by 120 degrees and the third lags the second by the same amount.
The power company's generators have three sets of coils, equally-spaced 120 degrees apart around a circle. Each coil produces one phase of electricity. Power comes from a utility in three wires, each carrying one phase. Homes get one or two phases, businesses get three phases.
The powerful AC motors used in industry are much like the power company's generator. These motors use three-phase electricity, driving the motor at high efficiency.