The difference between single-phase and three-phase 1. The main difference between the two is that the AC voltage is different, the former is 220 volts, and the latter is 380 volts. Three-phase AC power is also a form of transmission, with three power supplies that have the same frequency and amplitude, and are cross combined. Generally, it is used for power distribution or higher power equipment. 2. Single phase is mainly used for power supply of ordinary household or office appliances. The more vivid difference is that their waveforms and vector diagrams are different. When it comes to three-phase electricity, both are live wires, with 380 volts between them. Three-phase electricity can be connected to three motors and simultaneously enter the motor, using a star or triangular connection method.