AC circuits, which are usually three-phase, are used to distribute and transmit electricity. Single phase circuits are commonly used in our domestic electrical system.

 

The total power of a three-phase circuit is equal to three times the power of one phase. So if the power of one phase of the three-phase system is P, then the total power of the system will be 3P (provided the three-phase system is perfectly balanced). But if the three-phase system is not exactly balanced, the total power of the system will be the sum of the power of the phases.