ControlElectrical DesignHow ToMotorsThree Phase AC Circuits

Three Phase Motor Star/Delta Reverse & Forward without Timer

3-Phase Motor Connection Star/Delta (Y-Δ) Reverse-Forward & Up-down without Timer Power, Control & Wiring Diagrams

In this motor starter, there are four Contactors and switches (Two ON-Push and OFF-Push) are used to change the rotating direction of a three phase motor such as Revers, Forward, Up or down. As there is no timer used in the control circuit, the operation is semi-automatic or manual.

The power circuit and schematic wiring diagram shows that L1 and L3 have been changed for reverse and forward operation of the three phase motor (as changing two lines out of three will change the rotation of the motor in opposite direction). This kind of motor starting methods through motor starters are needed and used in lathe machines and cranes etc. to change the rotation of motors.

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Working of the Circuit:

  • If we press the pushbutton for Forward Operation, the motor will start in forward or Up position via K1 Contactor. Similarly, the pushbutton for Reverse operation is used to rotate the motor in Reverse or Down position via K2. Contactor (Where as two lines are changes with respect to the first contactor i.e. K1).
  • Keep in mind that only one operation (either forward or reverse) is possible at a time due to electrical interlocking i.e. if pushbutton for Forward direction is ON, we will have to stop the starter before changing the rotation of the motor. In simple words, both K1 (for Forward) and K2 (for Reverse) contactors can’t be ON at the same time.
  • K4 Contactor is in star connection while K3 Contactor is in Delta Connection. They are used as a Star-Delta starter where the motor connects to the main supply in star configuration initially (to reduce the high stating current) and then in Delta connection with full load speed and voltage.

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  • O/L = Over Load Relay (Thermal)
  • NO = Normally Open Contacts
  • NC = Normally Closed Contacts
  • FOR = Forward Position
  • REV = Reverse Direction
  • T = Timer
  • L1, L2, L3 = Three Lines or Phases
  • K1, K2, K3, K4 = Contactors
  • Y = Y or Star Connection
  • Δ = Delta Connection

Power Diagram

Power Diagram of Three Phase Motor Connection for Star/Delta starter without timer to operate the motor in Reverse / Forward directions.

Power Diagram of 3-Phase Motor Connection (Star-Delta) Reversing without Timer

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Control Diagram

Control Diagram of 3-Phase Motor Connection (Star/Delta starter without timer) for Reverse / Forward or Up-down operations.

Control Diagram of 3-Phase Motor Connection (Star-Delta) Reversing without Timer

Schematic Wiring Diagram

Schematic Wiring Diagram of 3-Φ Phase Motor Connection for Reverse and Forward operation using Star/Delta  starter without Timer.

Wiring Diagram of Star Delta Reverse Forward Connection without Timer

Related Power, Control and Wiring Diagrams for Motors

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