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Star Delta Starter – (Y-Δ) Starter Power, Control and Wiring Diagram

Automatic Star / Delta Starter with Timer for 3-Phase AC Motors

In this tutorial, we will show the Star-Delta (Y-Δ) 3-phase induction AC Motor Starting Method by Automatic star-delta starter with Timer with schematic, power, control and wiring diagram as well as how star-delta starter works and their applications with advantages and disadvantages.

Automatic Star Delta Starter with Timer Wiring & Installation Diagram

Star Delta Starter with Timer Wiring Diagram
Automatic Star Delta Starter with Timer For Three Phase Motor

Explanation of the working and operation of Star Delta Automatic Starter with Timer Wiring Installation:

From the left you have the main contactor with the pneumatic timer because your main contactor is always energized, in the Middle you have the Delta contactor with a thermal overload for motor protection in case the motor exceeds the ampere rating set on the thermal overload, on the right you have the Star contactor which is the first contactor to be energized with the main contactor then when the timer reaches its time limit the Star contactor de-energizes and the Delta contactor energizes and the Motor is running at full load.

Related Motor Control & Power Diagrams:

Operation & Working of Automatic Star Delta Starter

From L1 The phase current flows to thermal overload contact through fuse, then OFF push button, On push button Interlocking contact 2, and then C3. This way, the circuit is completed, as a result;

  1. Contactor coil C3 and timer coil (I1) is energized at once and the motor winding then connected in Star. When C3 is energized, its auxiliary open links will be closed and vice versa (i.e. close links would be open). Thus C1 Contactor is also energized and Three Phase Supply will reach to the motor. Since winding is connected in Star, hence each phase will get √3 times less than the line voltage i.e. 230V. Hence Motor starts safely.
  2. The close contact of C3 in the Delta line opens because of which there would be no chance of activation of contactor 2 (C2) .
  3. After leaving the push button, Timer coil and coil 3 will receive a supply through Timer contact (Ia) , Holding contact 3 and the close contact 2 of C2.
  4. When Contactor 1 (C1) is energized, then the two open contact in the line of C1 and C2 will be closed.
  5. For the specific time (generally 5-10 seconds) in which the motor will be connected in star, after that the Timer contact (Ia) will be open (We may change by rotating the timer knob to adjust the time again) and as a result;
  • Contactor 3 (C3) will be off, because of which the open link of C3 will be close (which is in the line of C2) thus C2 will also energize. Similarly, When C3 off, then star connection of winding will also open. And C2 will be closed. Therefore, the motor winding will be connected in Delta. In addition, Contact 2 (which is in the line C3) will open, by which, there would not be any chance of activation of coil 3 (C3)
  • Since the motor is connected in Delta now, therefore, each phase of the motor will receive full line voltage (400V) and the motor will start to run in full motion.

Related Post:

Star Delta Starter Power Diagram

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Star Delta starter Power Diagram
Star Delta starter Power Circuit Diagram

Control Diagram of Star Delta Starter with Timer

Click image to enlarge

Star Delta starter with Control Diagram
Star Delta starter with Control Diagram

Wiring Diagram of Star Delta Starter with Timer

Click image to enlarge

Wiring Diagram of Star Delta Starter
Automatic Star Delta (Y-Δ) Starter with Timer for 3-Phase Induction Motor

Abbreviations: ( FOR Control Wiring of Three Phase Star Delta Starter with Timer)

  • R , Y, B = Red, Yellow, Blue ( 3 Phase Lines)
  • C.B = General Circuit Breaker
  • Main = Main Supply
  • Y = Star
  • Δ = Delta
  • 1a = Timer
  • C1, C2, C3 = Contatcors (For Power & Control Diagram)
  • O/L = Over Load Relay
  • NO = Normally Open
  • NC = Normally Closed
  • K1 = Contactor (Contactor coil)
  • K1/NO = Contactor Holding Coil (Normally Open)

Related Posts:

Advantages & Disadvantages of Star Delta Starter with Timer


  • Simple Design and Operation
  • Comparatively cheaper than other voltage controlling methods
  • Torque and Current performance of the Star delta starter is well.
  • It draws two times starting current of the FLA (Full Load Ampere) of the connected motor.
  • It reduced the starting current to one-third (approximately) as compared to DOL (Direct ON Line Starter)

 Also read:


  • Starting Torque is also reduce to one-third because starter reduce the starting current to one-third of the rated current [as Line voltage also reduced to 57% (1/√3)]
  • It required Six leads or terminals Motor (Delta Connected)
  • For Delta connection, the supply voltage must be same as the rated motor voltage.
  • At switching time (From Star to Delta), if the motor does not reach at least 90% of its rated speed, then the current peak may be equally high as in Direct ON Line starter( D.O.L), thus it may cause harmful effects on the contactors contacts, so it would not be reliable.
  • We may not use star delta starter if the required (application or load) torque is more than 50% of the three phase induction motors rated torque

Related Post:

2 Speeds, 2 Directions Multispeed 3-phase Motor Power & Control Diagrams

Characteristics & Features of Star-Delta Starter

  • The starting current is 33% of full load current for star delta starter.
  • The peak starting torque is 33% of full load torque.
  • The peak starting current is 1.3 to 2.6 of full load current.
  • Star-Delta Starter can be used only for low to high power three phase induction motors.
  • It has reduced starting current and torque.
  • The 6 connection cables are needed for motor terminal box.
  • In Star Delta starter, Current peak and mechanical load on changeover from star delta

Applications of Star Delta Starter

As we know the main purpose of star delta starter is to start the three phase induction motor in Star Connection while run in Delta Connection.

While keep in mind that Star Delta starter can only be used for low to medium voltage and light starting torque induction motors. In case of direct on line (D.O.L) start, the receiving current at motor is about 33% while the starting torque reduced about 25-30%. This way, Star Delta Starter can be only used for light load during starting the motor. Otherwise, the heavy load motor wont start due to low torque which need to accelerate the motor to rated speed while converting to the Delta connection.

You may also read other power & control diagrams below:

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  1. MURSHED ALAM says:

    Its very usefully circuits .

  2. Its very usefully circuits .

  3. Binesh Vk says:

    should be use one more timer for disconnect Main and Star contactor … if delta contactor faulty. its very importend.<br />

  4. Nasir Uddin says:

    It&#39;s very inportant circuit for industrial aria

  5. Nasir Uddin says:

    It&#39;s very inportant circuit for industrial aria

  6. Anonymous says:

    i also have diagram but how can i sent it to u…but may be this one helps u star connection is A1 B2 C3 close the other ends and for delta connect A1 B2 , B1 C2 , C1 A2….

    1. Electrical Technology says:

      Dear…Upload it to our FB page…

    2. says:

      How this starter is built only combination of two contactors?

  7. learnmore marungisa says:

    i want about how to calculate a resistor.<br />

  8. Anonymous says:

    What is the use of timer in this circuit and how will delta operate after a delayed timing? plz analyse ur circuit once again

  9. Tanmoy Nandi says:

    Please Describe the the control circuit diagram of Automatic Star Delta Starter with Timer for 3-phase Motor

  10. Ajit singh says:

    Need ckt diagram fr three motor having star delta starter on same mcc such that only 2motor can start simultaneously not 3rd one

    1. Motor power rating, star or delta

  11. Anonymous says:

    the timer in the circuit is used to time out c3 and time in c2 .to understand it just identify the contact of the timer in the circuit .u will see one contact is closed for c3 and one open for c2

  12. It is a shematic diagram .I need wiring diagram of automatic star delta

  13. You need to elaborate more, in your diagram;how the contactors are energised and fully describe how it works.

  14. Are you sure it will work?
    You might do a review about the diagram,and correct me if im wrong, it doesnt work i think.

    1. Electrical Technology says:

      Please elaborate in detail.. Thanks

  15. khairul Basar says:

    Please help me,
    I need a ATS wiring diagram by using timers and relay (three phase system)


  16. norman peoples says:

    I once worked on a Large Burnt out 3 Phase Motor which was used for pumping sugar from the delivery Road Tanker Lorry into a Sugar Storage Tower Silo. My boss told me the windings were unusual because they were of a STAR STAR DELTA configuration ?

    Have you come across this type of motor windings arrangement before ?


    Norman Peoples


    send me the star and delta control drawing with timer

  18. Usman Shabbir says:


    Please show with real connection.

  19. MRINAL DAS says:

    Plz send me working principle and construction of semi automatic star delta starter….
    I can’t understand reletade website information….

  20. sunil vaidya says:

    information of condactor&timer

  21. Good day sir,please l will like to download some diagrams and note.

  22. I will lik to no more about star delta diagrams, the one I will understand well

  23. nilmani chubey says:

    Plz send me working principle and construction of semi automatic star delta starter….
    I can’t understand reletade website information….

  24. Anak Apai says:

    Hi, I have this winding automatic STAR DELTA with timer and the inverter (Hz) to operate the 3 phase motor at my workplace.
    Recently we have facing the motor was tripped and error shown at inverter display is “L In”, sometimes “OL”, sometimes”L U”, and “OV1” when tripped.
    Could someone advice how to troubleshoot this problem?

    Thanks Best Regards.

  25. ajay kumar says:

    dear, please tel me how to calliberate star delta with timer.

  26. ajay kumar says:

    how to calliberate star delta with timer. its urgent

  27. moh khlid says:

    I think In the actual built circuit shown as picture posted, the star contactor is connected to the thermal overload terminal from motor side, which is more safety may be, not from delta contactor side as shown in power circuit diagram.

    Thanks for your valued information, it realy helped me alot.

    1. Mohsin Ali Shah says:

      Mohammad Khalid,
      1.Current flowing through star contactor is very very less than the delta contactor.
      2. Star contactor is working only for some seconds and after that Delta contactor will work continuesly.
      Therefore thermal over load will never connected to star 🌟 contactor

  28. how can i create 555 timer circuit simulation into MATLAB.

  29. Bhagwan Lal Bhoi says:

    I am intrest in electrical work succes my life

  30. micheal pam says:

    the work is good but please how can i get the full materials on it.

  31. Youssef SALIMI says:

    thanks for your schematics
    i made the start delta control circuit in fluid-sim, and i releized that it repeat the cycle when you press the start button again, and as solution i suggested to energize the main contact first.

    1. Mohsin Ali Shah says:

      Youssef Salimi.

      I think you not put NC contact of delta contactor C2 between start push and Delta contactor coil, that’s why it repeat the sequence when you push the start again.
      Please check your connection diagram you made in fluid-sim.

  32. i do not understand how can coonection the star delta motor please help me

    1. Wiring connection reference will be near the terminal box of motor or the terminal box cover. This circuit is concept of star start delta run motors. Main supply will be connected to U1, V1, W1 and the configuration of star or delta will be based on the active contactor. Timer is to delay the turning off of the star contactor and delaying the turning on of the delta contactor. But what if the voltage of start is different from the run voltage?

  33. Tapas Biswas says:

    Please inform me have any Dealer of Automatic Star Delta Starter for 10Hp motor pump in Kolkata market? Give me address and contract no.

  34. pls can I get any written project on a star delta control panel circuit with timer from you plssssssss

  35. michael costello says:

    Very good article. Thank you

  36. Stanley Kaundula says:

    Please assist me on where in the circuit to connect lamps to show that it running and a siren aswell

    1. Mohsin Ali Shah says:

      Run inductor lamp you can connect parallel to the main contactor C1 or in series of any free NO(Normally Open) contact of C1 and trip inductor lamp or siren can be connected in series of NO (Normally Open) contact of Over Load protector.

  37. Getinet Habtamu says:

    Your website is very important for those engineering students go ahead.

  38. oluka wilson says:

    thanks sir you have taught us and imparted us knowledge on electrical

  39. Ihsan Muhammad says:

    Thanks for your information.,,

    very usefull

  40. Atheer Polus says:

    Kindly what rates required for motors of 200 H.p for cont actors, main circuit breaker of start delta

    How We can calculate for various motor power rate ?!


  41. sanjiv kumar says:

    can we use H r c fuses for more safety of motor

  42. Admire Chiminya says:

    The diagram is well presented and the Star delta is correct but the start/stop and the timer looks chaotic or not clearly illustrated

  43. Mohsin Ali Shah says:

    Thanks for sharing, it is a good information.
    And Why 2 Overload protector relays? In second diagram.

    Waste of material!!!!
    Only one is enough as the current is flowing in series with both the OLs.

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