I am creating a schematic for my machine which is supposed to do the following with the push of a button. All motors are three-phase AC motors.

  1. Run Motor 1 CW until it hits its right limit switch.

  2. Then run Motor 2 CW for a given time with using a timer relay.

  3. Then run Motor 1 in CCW until it hits its left limit switch.

Should I be using two contactors for Motor 1 or can I create a schematic in which both motors only have 1 contactor and the rotation is switched by something else?

I am not very knowledgeable of PLCs.

I would like to keep my costs low while still building a reliable system.

I would like to learn more about how to address changing rotation in terms of relay logic and necessary components.

I would also appreciate any further resources that could assist me when building such a schematic for 3-phase AC motors using relay logic.


3 Answers 3


Two contactors are a must to change the phase sequence for reversing a three-phase motor.

The power and control circuits are as shown.

enter image description here

When a cycle is initiated, on resumption of power after an interruption, the machine will complete the interrupted cycle.

  • \$\begingroup\$ Is there a reason why you numbered motors differently? Aren't they both supposed to be M1? \$\endgroup\$ Commented Jul 23, 2023 at 9:37
  • \$\begingroup\$ Hi Burak, M1 is the reversing motor that runs CW and CCW and M2 the motor that runs CW only. \$\endgroup\$
    – vu2nan
    Commented Jul 23, 2023 at 10:59
  • \$\begingroup\$ Oh, alright I see. Sorry, I confused contactors and MPCBs. Then, are MPCBs thermic relays? \$\endgroup\$ Commented Jul 23, 2023 at 12:05
  • \$\begingroup\$ Hi Burak, MPCB stands for Motor Protection Circuit Breaker. An MPCB is a specially designed circuit breaker for protecting electric motors against overload, short circuit, under voltage and phase loss. \$\endgroup\$
    – vu2nan
    Commented Jul 23, 2023 at 17:55

Changing rotation on a 3-phase motor is rather simple. Just pick any two phases and swap them.

I would think you would want a 3rd mode where the motor is not turning, simply disconnect those same 2 phases (the 3rd phase can be left connected). I would dwell in this position for a short time rather than do an immediate reversal. So 3 modes:

  • Fwd - L1 to A, L2 to B, L3 to C
  • OFF - L1 to A, L2 to nothing, L3 to nothing
  • Rev - L1 to A, L2 to C, L3 to B

You will want some sort of interlock so it is impossible for both directions to be selected at once: if you connect L2 to B and also L3 to B, that's a dead short.


I am not familiar with 3 phase AC motors only BLDC motors. You can easily reverse the direction of a bldc motor by switching one phase leg. It can be easily done especially if there are hall sensors being used. I have successfully converted an automobile alternator into a 3 phase DC brushless motor. The bridge rectifier is removed and identify the 3 plase wires. youll either be in a WYE or Delta config. The brush connectors then get powered with DC voltage and you have a powerful brushless 3 phase DC motor. configuration


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.