In general, AC power distribution systems are classified as single-phase, two-phase, or three-phase.

Single-phase circuits involve a single source connected to the loads through two-wire systems.

Single-phase systems are used in households to power 120-V and 240-V appliances such as lamps, TVs, or central air conditioners.

A two-phase three-wire system has two sources, where the voltage generated by the second one lags the other by 90 degrees.

In contrast, a three-phase four-wire system consists of three sources with the same amplitude, frequency, and phase difference of 120 degrees, connected to three loads.

The three-phase source and three-phase load can be either Y- or delta-connected.

These circuits are used in industrial applications like powering an induction motor, when required, they can be used to provide single-phase inputs.

The instantaneous power in these systems has a much lower pulsation than that delivered by a single-phase system, ensuring a more uniform power transmission and less vibration.

They require less conductor material or wire to transmit the same power, making them more economical than the single-phase.