Why starter is use- At the time of starting the motor draws 4 to 5 times of the rated current of the motor. For which because of maximum current at the starting the winding may burn. To reduce the starting current of the motor starter is used. The starter should be connected in between source to load and should be connected in series with it.

According to the design the starter can be of following types-

  1. DOL
  2. Star-Delta

DOL (Direct ON Line)-

This starter has 2 power sections-

1.Main power

2.Control power

Generally small motors practically up to 11KW, the starter winding is designed in such a way that it can withstand the direct starting current. So we can provide the 3 power directly to the motor along with some protection named as DOL .

In power supply system, the 3 power passes through MPCB to contractor and the output of the contactor is input for the motor. By switching ON the MPCB,3 power will input for the conductor after peak up of the conductor the supply reaches to motor and the motor runs. The contactor peak up is controlled by control supply.

The control supply can be 24V, 110V, 230V or 440V. The control supply passes through MCB the phase passes through over load-stop(NC)-selector switch-start(NO)-and coil point of the contractor. The neutral is directly connected to another point of the coil of the conductor. While latching(holding) point is arranged in parallel with the start push button through No point of contactor.


Whenever the start push button is activate the contactor will become after releasing the start push button the contactor remains ON condition due to holding point. When the stop push button activate the supply is connect from the contactor for which it will open and the motor will stop.

If the motor will draw more current than the MPCB current setting it will trip indicate the overload will active so again the power supply to the contactor disconnect.


Generally this feeder used for motors rated more than 11KW. In power supply warning , 3 supply pass through MCCB and through over load. 3 contactors, main contactor K1, star contactor K2 , delta contactor K3 is arranged. The output of MCCB is the input for K1 with proper p phase reverse sequence input for K3. The output of K1 is input for the 3 terminal of starter. One end of the gate is shorted the output terminal of K2 and K3 is the input for other 3 terminals of starter.

The control supply is arranged for all the contactors the phase passes through MCB-overload(NC)-All stop(NC)-Selector switch-start(NO) and the coil point of K1.

Again from the input of coil point of K1 for star timmer NC-K3NC-K2 coil point.

For delta K2NC-timmer NO and the coil point of K3.

The same supply is given to the coil point of the timer. Which is a delay time.

All the other coil of contactor and timmer is connected through the MCB.

The holding and latching point of K1 , in NO connect in parallel with start push button.


When the start push button operates K1 and k2 will pick up and at the same time, the timmer will be activated. So the motor runs with a star connection. After the time setting of the timer 8 to 11 sec, the timmer will be ON. So K2 will be disconnect from the supply and K3 pick up for which the motor runs with delta connection.

When the stop push button activate the supply disconnect from the contactor for which it will open and the motor will stop.

If the motor will draw more current than the MCCB current voltage setting , it will trip indicate the overload will activate. So again the power supply to the contactor disconnected.

Sachidananda Dhar

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