What is Star Delta Starter Circuit?

What is Star Delta Starter Circuit?

Have you ever heard of a star-delta starter circuit? If not, don’t worry, you’re not alone. In fact, most people have never heard of it. But if you’re an electrical engineer or someone who works with electrical circuits, then you’ll definitely want to know what a star-delta starter circuit is.

In this blog post, we will discuss the basics of star delta starter circuits, including how they work and some of their benefits.

What is Star Delta Starter Circuit?

A star delta starter circuit is a type of electrical starting system that is commonly used in industrial and commercial applications. It is used to start electric motors by providing a reduced voltage to the motor [1].

In addition to starting electric motors, a star-delta starter circuit can also be used to provide a reduced voltage to other types of loads, such as fans, pumps and compressors.

The most common type of star delta starter circuit is the three-phase star delta starter. It is connected to the motor through a set of contactors.

What is Star Delta Starter Circuit?

The star delta starter circuit is one of the most popular electrical starting systems because it is reliable and efficient. Additionally, it can be used with a variety of different types of loads.

If you are looking for an electrical starting system for your application, the star delta starter circuit is a good option to consider.

Advantages and Disadvantages of Star Delta Starter Circuit


These starters are popular because they provide a number of advantages over other types of starters.

  • The main pro is that they reduce the inrush current during start-up. This is because the motor winding resistance is lower in the delta connection than when the motor is connected directly to the power supply in the star connection. As a result, the starting torque is also reduced, which can be an advantage in some applications.
  • One of the great things about star-delta starters is that you can use them with a wide range of motors and sizes. For example, they can be used with both induction and synchronous motors.
  • They are also relatively simple to construct and operate, which makes them a cost-effective option for many applications. This means that they can be used in a wide range of industries, from domestic to industrial.
  • One advantage of using a star-delta starter is that it can help extend the life of your motor. By starting the motor in star mode, you are applying less stress to the motor than if you were t to start it in delta mode. This can help to prolong the life of your motor, as well as improve its efficiency.
  • Finally, star-delta starters can be used with either three-phase or single-phase power supplies. This makes them a versatile option for many different types of applications.


These starters are not without cons too, however.

  • It requires more maintenance – The reason for it is that the star-delta starter uses a lot of contacts. These contacts can wear out over time, and they need to be replaced.
  • It can cause problems with the motor – The star-delta starter can cause problems with the motor, such as vibration and noise. This is because the star connection has a lower impedance than the delta connection.
  • It is not suitable for all applications – The star-delta starter is not suitable for all applications. For example, it is not suitable for use with pumps and fans.
  • It is not as reliable as other methods – The star-delta starter is not as reliable as the soft start or the variable speed drive. This is because it uses a lot of contacts, which can wear out over time.

Advantages and Disadvantages of Star Delta Starter Circuit

Where is a Star Delta Starter usually used?

There are a lot of industrial applications that would use a star-delta starter. One example is when you have a three-phase induction motor that is started frequently throughout the day.

Another common application is with compressors, pumps, and fans. If any of these pieces of equipment are started and stopped often during the course of a day, then these starters are a good option.

They are also used in conveyor belts, cranes, and other heavy machinery. Basically, any time you need to start and stop a three-phase motor frequently, a star-delta starter is a good option.

The last place you might see a star-delta starter is in a machine that has a high inrush current. This could be something like a furnace or an oven. If the motor for one of these pieces of equipment needs to have a high starting torque, then a star-delta starter can provide that.

How does it work?

A star-delta starter is basically a way to reduce the amount of inrush current when starting a three-phase motor. In other words, it’s a way to make sure that the motor doesn’t draw too much current when it’s first turned on.

The way it does this is by starting the motor in what’s called the “star” configuration. In this configuration, the three-phase windings are connected together in a star pattern.

Once the motor is up and running, the star delta starter will then switch the winding configuration to what’s called the “delta” configuration. In this configuration, the windings are connected in a delta pattern.

This allows the motor to run at full power.

How does it work?

The star-delta starter will then switch back to the star configuration when it’s time to turn the motor off. This helps to reduce the amount of current that flows through the motor when it’s turned off, which can help to prevent damage to the motor.

So that’s a basic overview of how star-delta starters work.

Open transition star-delta starting

This design uses a three-phase contactor to connect the motor windings in either the star or delta configuration. A timer is used to delay the application of voltage to the delta winding, which reduces the inrush current during starting.

The main advantage of this type of starter is its low cost. Moreover, it is simple to wire and does not require a maintenance switch.

However, the main disadvantage is that it does not provide any protection against phase loss or unbalanced voltage conditions.

In addition, the open transition design can cause a momentary power interruption to connected loads when the contactor switches between the star and delta configurations.

Closed transition star-delta starting

This type is a more sophisticated design that uses two three-phase contractors too.

This type of starter does not require a timer. In addition, the closed transition design eliminates the power interruption that is caused by the switching of the contactors in the open transition starter.

However, the closed transition starter is more expensive than the open transition starter.

It is also more difficult to wire, and it requires a maintenance switch.

Closed transition star-delta starting

The main advantage is its reliability. It is the most reliable type of starter, but it is also the most expensive.

For this reason, it is often used in mission-critical applications where downtime must be minimized.

Parts of a star-delta starter

There are three main parts to a star-delta starter: the motor, the contactor, and the overload relay.

  • The motor is the part of the starter that actually turns the engine over. It is usually a three-phase induction motor. Actually, any type of motor can be used, but three-phase induction motors are the most common.
  • The contactor is the part of the starter that controls the flow of electricity to the motor. It is usually a heavy-duty switch that can handle large amounts of current. Moreover, the contactor must be able to switch the current on and off quickly.
  • The overload relay is the part of the starter that protects the motor from damage due to overloading. It is a thermal or electronic device that trips when the current flowing through it exceeds a certain level.

When all three of these parts are put together, they form a star-delta starter.

However, there are other parts that are sometimes included in a star-delta starter.

  • For example, a timer is often used to delay the energizing of the delta winding. This prevents the motor from starting under full load, which could damage it.
  • In addition, a push-button is sometimes used to manually switch the starter on and off.
  • A pilot light is another common feature. It indicates whether or not the starter is energized.
  • Last but not least, a reversing contactor can be used to reverse the direction of rotation of the motor.

All of these features are optional, and it is up to the designer of the starter to decide which ones to include.


There are a few things to keep in mind when using a star-delta starter circuit.

First, make sure that the voltage and current rating of the contactor is appropriate for the application.

Second, be aware of the inrush current when the motor starts up. This can cause problems if the contactor is not sized properly.

Lastly, make sure that the star-delta starter is properly wired and that all connections are tight.

If you follow these tips, you should be able to use a star-delta starter circuit without any problems.


What is the difference between a star-delta and a DOL starter?

  • A star-delta starter will initially connect the motor to the power supply in a star configuration. This means that only two of the three phases are connected, resulting in a lower current flowing through the motor. Once the motor has reached a certain speed, the starter will then switch the connection to a delta configuration.
  • A DOL starter, on the other hand, will always maintain a delta configuration. This means that all three phases are connected from the start, resulting in a higher current flowing through the motor. However, this also means that the DOL starter is more likely to cause damage to the motor if it is not used correctly.

Is star-delta a soft starter?

Yes, star-delta is a type of soft starter. A soft starter is a device that is used to slowly ramp up the voltage and current to a motor. This reduces the amount of stress on the motor, which can prolong its lifespan.

Where starters are usually used?

Starters are typically used in applications where the motor needs to be started and stopped frequently. This could be something like a conveyor belt or a pump. Starters can also be used in applications where the load on the motor is high, such as a crusher or mixer.

Useful Video: Star Delta Starter Explained – Working Principle

Final Thoughts

Overall, the star delta starter circuit is a great way to get your motor started. It’s simple to set up and can be done in just a few minutes. Plus, it’s relatively inexpensive and easy to find the parts you need.

If you’re looking for an easy way to get your motor started, the star delta starter circuit is definitely worth considering.

I hope this article has helped you understand what the star delta starter circuit is and how it works. Thanks for reading!

P.S. If you found this article helpful, please consider sharing it with others who might benefit from it. Thanks!


  1. https://engineerfix.com/star-delta-starter-circuit-y-%CE%B4-how-to-wire-pros-and-cons/