Single phase Direct online starter (DOL) is a device consist of main contactor, protective devices and overload relay which is used for motor starting operations. It is used for low rating usually below 5HP motors.
Why do we need DOL starter?
At startup, the induction motor consumes a significant quantity of current. The motor windings may sustain damage from this beginning current. We employ many methods to lower the beginning current employing Motor Starters (such as star delta or DOL starters) in order to prevent any harm. The motor ratings and the load attached to the motor determine these methods. In addition, the motor starter guards against over-current and overloading.
NOTE
By connecting the motor directly to full power via an MCCB or circuit breaker and relays for overload protection, the Direct Online or DOL starter uses the full voltage or across the line starting technique. For this reason, induction motors rated under 5 horsepower are equipped with such a starting.


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