Flowchart schematic diagram for the Control Circuit of a Star Delta or Wye Delta Electric Motor Controller - A how to learn skills training guide for electric motor controller

To help facilitate for a better understanding and further learning and training of the concept of the star delta or wye delta control (ckt) circuit covered in our previous article, a flowchart diagram is presented below as a follow up learning guide which shows a schematic representation of the sequence of operation for the starting and stopping and running operation of the star delta or wye delta electric motor control circuit in order to provide a visual aid to help diagrammatically visualize how the control circuit flows.

The electrical schematic diagram of a star (wye) delta electric motor control (ckt) circuit:

The parts of the star (wye) delta electric motor control (ckt) circuit includes:

1. OFF push button switch (Normally-Close Contact) - 1 piece
2. ON push button switch (Normally-Open Contact) - 1 piece
3. Main Contactor Coil - 1 unit
4. Thermal Overload Relay (Normally-Close Contact) - 1 piece
5. Main Contactor Auxiliary Contact (Normally-Open Contact) - 2 pieces
6. Timer Coil - 1 piece 
7. Timer Contact (Normally-Close Contact) - 1 piece
8. Timer Contact (Normally-Open Contact) - 1 piece
9. Star Contactor Coil - 1 unit
10. Star Contactor Auxiliary Contact (Normally-Close Contact) - 1 piece
11. Delta Contactor Coil - 1 unit
12. Delta Contactor Auxiliary Contact (Normally-Close Contact) - 1 piece

The flowchart diagram of the star (wye) delta electric motor control (ckt) circuit:
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Procedural sequence to learn about the method of operation of the star (wye) delta electric motor control (ckt) circuit:

1. RUN MODE: The operator presses the ON push button switch. With the OFF push button switch and the thermal overload contact remained close at OFF state, then current flows down to the main contactor coil.
2. When the main contactor coil is energized, its auxiliary contact connected in parallel across the run push button switch closes which serves as a holding contact to maintain the main contactor coil energized after the operator releases his finger from the ON push button switch.
3. While the normally-close contact of the timer and the delta contactor are yet inactive at close state, another normally-open contact of the main contactor closes, which permits power flow to the star contactor coil and the timer coil, thereby placing the motor terminal connected in star configuration. 
4. With the timer coil activated, the timer starts to count up until it reaches its specified time period. Once the elapse time is up, the normal state of the timer contacts changes state from close to open and from open to close.
5. The elapsed time will open a timer contact to remove power flow to the star contactor coil thereby releasing the motor from star configuration, while at the same time another timer contact will close to permit power flow to the delta contactor coil to reconfigure the motor terminal to a delta connection.
6. During the initial start sequence wherein the star contactor coil is active, its auxiliary normally-close contact is opened to prevent power flow to the delta contactor coil. And then when the control circuit switches to the delta mode with the activation of the timer, the auxiliary contact from the energized delta contactor coil would also be opened to prevent power flow to the star contactor coil. These interlock contacts that are each connected in opposite order to the star and delta contactor coils are intended to prevent the simultaneous activation of both star and delta contactor coils.
7. STOP MODE: Operator presses the OFF push button switch. This action disconnects the control (ckt) circuit from the power source which prevents power flow to all energized contactor coils including the timer coil as a result of the opening of the normally-close contact of the OFF push button switch.
8. CIRCUIT INTERRUPTION: The thermal overload relay detects motor overload current, which when detected will activate the thermal switch to open its normally-close contact to isolate power flow to all energized coils in the circuit, thus, deactivating the control circuit.

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