How to setting the timer for star delta starter?

How many second we need to setting for changeover timer from STAR to DELTA sequence for Star Delta Starter?This question is very popular among electrician around the world when handling the Star Delta Starter for their application.

From my experience,honestly,it quite difficult to get the accurate times for star delta changeover.But we can get the approximate times with several monitoring technique and measuring equipment to decide the best setting for change over timer of Star Delta Starter.From this post,i would like to share some information and basic technique how to get the approximate times for Star Delta Starter change over timer.I hope from this post,it’s can give some ideas or clear view how to setting the times for Star Delta Starter change over timer.

How to get a time for change over of Star Delta Starter?

The important point that we should know about Star Delta Starter is when in STAR sequence it must running with 80% of full load speed for motor before change over to DELTA sequence.

From this point we can use it to get the approximate time for change over timer.Basically we can use the two measuring method following :-

1) Clamp on meter / ampere meter

This method we can measure the ampere during STAR sequence.It’s can start from 0 (zero) until peak value of ampere and it will in flat reading because the voltage applied for star delta starter to the individual motor winding is therefore reduced by a factor of  1√3 = 0.58 this connection amounts to approximately 30% of the delta values.

Prepare the stop watch to measure the time from 0 (zero) ampere until peak value during STAR sequence.After that use the time that we measure to setting change over for the Star Delta Starter timer.We need minimum two person to perform this measuring and start stop the starter.

2) RPM meter

This measuring method using the RPM meter to measure the speed of motor in RPM (Running Per Minute).Get the information for Full speed of motor at the motor nameplate eg ; 1400 rpm.

We can measure the speed of motor when space is available or the pulley or shaft not covered such as air-compressor.From the basic point for Star Delta Starter is it must running 80% of speed of motor,we can measure the speed of motor (RPM) during STAR sequence.

Set the stop watch and measure the time from starting (0 rpm ) until it reach 80% of motor speed.example if full motor speed is 1400  rpm,so for 80% full speed is around 1,120 rpm.So stop the watch and take the time reading.

That is the time for change over from STAR to DELTA sequence.Setting your timer with the time that we record and test run for full sequence and take a look if it have any abnormal phenomena.


Conclusion about timer setting for Star Delta Starter

These two method that i’d explained above is a basic measurement technique that we can use to determine the approximate time for change over of star delta starter.

It’s not 100% accurate but at lease we can get the approximate time for change over timer of Star Delta Starter.Normally the base line for timer setting is around 10 until 20 second.

We can use the try and error method to get the best time for change over from STAR to DELTA.Any suggestion,ideas or comment,please share it on my comment box.We can discuss this issue from different perspective.


  1. i wont tech…

  2. this is one of the best web side for me as a electrical technician thanks for awareness

  3. I very rarely discuss these posts, but I assumed this on deserved a well done

  4. mumtaz says

    Sir very good try to explain star delta. Thanks for sharing knowledge.

  5. Lovely blog, it loads very fast and appears very cool.

  6. Siddiq says

    This is one of the best web side for me as a electrically thanks for awareness

  7. Thanks for sharing your thoughts and awareness.

  8. Ahmed Hassaan says

    very useful, thank you sir

  9. Dear sir
    Please me need star delta daigram

  10. First method is not clear
    Any explanition?

  11. Prithivi raj thapa says

    It’s automatically trip the moter starter afer few running of moter , what would be reason ???

    • Thermal overload relay not selected or set properly.
      Insufficient horsepower to accelerate load properly.
      Time delay not long enough to reach 80% point as described above.
      Check the design.
      Check the components.
      Check the settings.

  12. khanyisani says

    my timer is not changing over what could be a reason?

    • Defective timer.
      Pneumatic timer or electronic timer, when the contactor closes and activates the time-delay-on timer, and it never times out, it’s broken.

  13. Defective timer.
    Pneumatic timer or electronic timer, when the contactor closes and activates the time-delay-on timer, and it never times out, it’s broken.

  14. Hemrajbhai dabhi says

    Sir, thanks for this post
    This post is very help for me.
    I need one more help, can we make “reverse forward type star Delta starter”?.

  15. canh le hoang says

    thanks for your post;
    I have a quetion: Can you tell me the range of power which we can apply star-delta starting? thanks!

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