What are electrical phases?

The mains supply to most homes is a single phase alternating current (AC) supply. Unlike the current supply from a battery which is a direct current (DC) supply, the current is constantly alternating between zero and peak values in a cyclical wave form shown below.                         Current constantly alternating between zero and peak value in a cyclical wave

The speed at which this cycle changes is known as the frequency of the supply. In the UK this supply frequency is 50Hz or 50 times per second.

For most domestic purposes this alternating supply is sufficient but for many commercial and industrial purposes it is necessary to improve power and efficiency by using a three phase supply. With a three phase supply each phase set to be separated by 120°. As shown below; Improving power and efficiency by using a three phase supply

A three-phase system is usually more economical than single-phase as reduced conductor material is required to transmit electrical power.

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