Star-Delta Starter PLC Program and Wiring - Part 5

To start your motor with star-delta start method, you need 3 contactors. One for turning the motor on and off, one to connect the motor windings in star, and one to connect the windings in delta. In Star-Delta Starter Part 5 you’re going to learn how to change the winding connections of a three phase motor from star to delta and vice versa using contactors.

To run a 3 phase motor under normal circumstances, you connect the three-phase power to the incoming terminals of the motor in the terminal box.

But to better control the motors run request, you can add a contactor in the way of incoming power.

If you want the motor winding connections to be in star, you can add a contactor and then connect the power contacts of the contactor to the W2, U2 and V2.

If you short circuit the other ends of the contactor’s contacts, when these contacts are closed the three motor terminals will be connected and the motor winding connection will be in star.

With this wiring, when both the main and star contactors are energized at the same time, you can say that the motor has started in star connection.

In this situation the main contactor works to flow the power to the motor and the star contactor connects the right side motor terminals together and sets the connection in star.  Simple, right?

Now let’s see how you can connect the motor windings in delta. To do this you need to add another contactor. I’ll call this the delta contactor. To connect the motor windings in delta, just as you did for the star connection, you should first wire the three main contacts of the contactor to the right side motor terminals.

You then need to wire the other ends of the contactors contacts to L1, L2 and L3 respectively.

Now, what happens in this situation? When both the main and the delta contactors are energized and the contacts are closed, U1 will be connected to W2, V1 will be connected to U2 and W1 will be connected to V2 and this is what you need to have the motor winding connections in delta.

So when the main and star contactors are energized at the same time the connection will be in star and when the main and delta contactors are energized the connection will be in delta.

There are no buttons on these contactors where you can demand the contactors contacts to be closed or opened. So to energize the contactors, you have to connect them to an industrial controller like a PLC. In the next lesson, you’re going to learn how you can control these contactors using a PLC.

If you have friends, clients or colleagues that would like to learn about start-delta wiring, please share this post. Thank you so much for watching and joining the conversation.

With so much love,

The RealPars Team

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Star-Delta Starter PLC Program and Wiring - Part 4

‍Star-Delta Starter PLC Program and Wiring - Part 6

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