A DOL Motor Starter (Direct On-Line Motor Starter) is an electrical circuit used to start and stop three-phase induction motors without the need for a soft starter or a variable frequency drive. It is the simplest and most cost-effective way to start and control a motor. The DOL Motor Starter consists of a contactor, an overload relay, and a start-stop push button. The contactor is a switch that is used to control the flow of electrical power to the motor. The overload relay is designed to protect the motor from overheating due to high currents. The start-stop push button is used to start and stop the motor.
When the DOL Motor Starter is energized, the contactor closes and the motor is connected directly to the power supply. This results in a high starting current, which can be up to seven times the rated current of the motor. The overload relay monitors the current flowing through the motor and disconnects the circuit if the current exceeds a preset value. The DOL Motor Starter is commonly used in applications where the motor load is low or the starting torque requirement is not critical, such as in pumps, fans, and compressors. It is also used in applications where the motor is started and stopped frequently. However, it is not suitable for applications where the starting current may cause a voltage drop in the power supply or damage the motor windings.
The DOL Motor Starter is simple to install and maintain, and is a reliable and cost-effective way to start and control three-phase induction motors.