A star-delta starter is a device that enhances the efficiency of a three-phase motor. The device limits the electrical current to the motor on startup while allowing full voltage when the motor reaches full speed.
The electrical current required to start any heavy-duty electric motor may be four times greater than its normal operating power requirement. When a three-phase motor starts up it is necessary to regulate this electrical current, changing the connections from "star" to "delta" at exactly the right moment. A star-delta starter is a special circuit that regulates these winding electrical configurations. As the most commonly used reduced voltage starters, the star-delta starter reduces startup wear and tear on motors, making them last longer.