There are two popular kinds of electrical systems, single phase and three phase. In a single phase system, current flows through a live wire and a neutral return path.

In a three phase system, there are three live wires and a common neutral return path.

The advantages of a three phase system are increased power delivery, cheaper generation and transmission.
Three phase voltage is generated by 3 coils with a separation inside a generator. Each coil voltage lags the other by