Star Delta Reversing Starter Wiring Diagram

 A star delta reversing starter, in addition to selecting the direction of rotation, allows the motor to start connected in a star and then remain connected in delta.

 With a star delta starter (Y-Δ starter) we want to reduce the starting current, so it is initially connected in “Y” supplying a lower voltage (starting voltage = nominal voltage /1.73). And some time later it is connected in a triangle.

The contactors KM1 and KM2 select the direction of rotation of the motor, KM3 connects in star and KM4 in delta.

Star Delta Reversing Starter Control Diagram

 Operation: we manually close the disconnector with fuses Q1, press the start push button S2, (column 1 of the control diagram) energizing the coil KM1, KM1 closes the contact (13,14 column 2), allowing KM1 to remain energized even when releasing the S2 button; in column three it opens the contact (31 and 32) to prevent the motor from being commanded to rotate in the other direction.

It also closes the contact (53 and 54) in column 5 allowing KM3 (star connection contactor) to be energized, KM3 prevents it from being connected in delta (contact 31 and 32 of KM3) and feeds the control relay KA1 (Contactor auxiliary KA1).

KA1 has a timed contact (contact 55 and 56) that after a preset time will disconnect the star contactor and allow the delta contactor to be powered.