The DOL or “direct on line” motor starter is a combination of electrical components wired together in a way that will start a motor directly. In other words, full power is applied to the motor as soon as the start signal is initiated.
How It Works
A DOL motor starter starts a motor straight away as soon as a start signal is initiated. Check out this electrical circuit of a DOL starter for a 3 phase motor.
If the start button in the control circuit is pressed this will provide power to K1 (the contactor coil), now that K1 is energised the 3 main contacts of K1 in the power circuit will close. This will provide full power to M (the motor) immediately. At this time, the K1 auxiliary contact will also become closed. Once someone takes their finger off the start button, the start button contact will become open circuit. But the K1 auxiliary contact will stay closed providing another current path to the K1 coil, thus keeping it energised. The motor will keep spinning until the stop button is pressed.
To Recap
The DOL motor starter is an installation of electrical components wired together in such a way so that they will power up a motor as soon as a start signal is given.
Learn more
Fundamentals of Electrical Controls
3 Phase Motor Control Bootcamp
Learn Variable Frequency Drives