Three-phase wiring provides three alternating currents uniformly separated in phase angle so that each leg of alternating current reaches its maximum voltage one-third of a cycle before and after the other two. This means the total amount of power supplied by all three alternating currents when added together remains constant. Three-phase power may be supplied via three wires or four.
Rotating a magnetic field through the conductors of a stationary coil produces a single-phase alternating current. If three conductors are 120 degrees apart around a central rotating magnetic field, they produce three alternating currents 120 degrees out of phase with each other. This configuration supplies three-phase power.
The two three-phase configurations are delta and wye. In a delta configuration, the three separate inductive loads are connected in triangular configuration, resembling the Greek letter "delta," with an electrical line connected to each point of the triangle. In a wye configuration, the three inductive loads radiate from a central point, resembling an English letter "Y," with an electrical line connected to each branch, and a fourth neutral wire connected to the central point where the loads meet.
A three-phase motor, with one set of windings for each phase, is highly efficient. The constant power supply allows a three-phase motor to draw significantly less current than an equivalent single-phase motor.