Electrical Wiring Diagram Forward Reverse Motor Control and Power Circuit Using Mitsubishi PLC

This blog post is not only intended to provide a graphical illustration but will also explain the procedure and the operational concept involving the wiring principle of the forward reverse motor control circuit with the use of a PLC (Programmable Logic Controller).

A diagram of the ladder program contained inside the PLC memory specifically for this function is also included below to clearly illustrate the operational sequence for command execution of this motor control system.

The electrical components comprising the hardware parts of the circuit includes:
1.) 440 volts to 220 volts step-down transformer - 1 piece.
2.) 220 volts to 24 volts step-down transformer - 1 piece.
3.) 24VAC to 24VDC power supply converter - 1 piece.
4.) Normally-open push button switch - 3 pieces.
5.) Mitsubishi PLC (Programmable Logic Controller) Type FX2N-16MR-ES - 1 unit.
6.) Auxiliary Relay with 24VDC coil with normally-open contact - 2 pieces.
7.) 3 phase 440 volts AC NFB (No-fuse breaker) circuit breaker (ampere rating depends on motor capacity) - 1 piece.
8.) 3 phase 440 volts AC magnetic contactor with 220 VAC coil (amper rating depends on motor capacity) - 2 pieces.
9.) Thermal overload relay (ampere rating depends on motor capacity) - 1 piece.
10.) 440 VAC induction motor (motor capacity depends on application) - 1 unit.

Figure 1 below shows the electrical wiring diagram of a typical forward reverse motor control and power circuit with PLC connection. Alternatively, you can open the drawing in new window for a more legible view.

Fig. 1: Electrical Wiring Diagram Forward Reverse Motor Control and Power Circuit with PLC Connection

Circuit Description:
Figure 1 above illustrates the power circuit physically wired in accordance with the usual three phase forward and reverse motor control circuit, wherein two magnetic contactors are utilized to suit the purpose of conveniently switching the motor terminals to easily accomplish the forward and reverse wiring configuration of the induction motor. The forward contactor is wired in the normal direct phasing of the motor terminal, whereas the reverse contactor is wired with two of the motor terminals in the opposite phase in order to reverse the rotational direction of the motor.

The control circuit which commands the switching selection of these two magnetic contactors is contained inside the PLC memory instead of the conventional method of making use of physically wired component assembly consisting of a combination of relay logic switches so connected to a conditional arrangement to create the control circuit.

Only the push button switches, the thermal overload contact and the auxiliary relays are externally connected to the PLC. The input terminals where the push button switches are connected is located on the upper part of the PLC, while the lower part is devoted to the output terminals of the PLC where the auxiliary relays are connected. So, we have the input terminal for operator intervention access command which is then processed internally by the ladder program contained inside the PLC memory, and then we have the output terminal which activates the corresponding auxiliary relay to subsequently energize the relevant magnetic contactors in the power circuit.

Figure 2 below shows the ladder program for the forward reverse motor control circuit contained inside the PLC memory. All of the sequential switching function of the control circuit is manipulated by the internal program constructed inside the PLC memory, which is easily done by means of drawing the wiring diagram of the logic sequence using the ladder programming editor of the Mitsubishi PLC software as shown in the following illustration.