FreertosHow-ToBeginner · 4 min read

How to Create Start Stop Motor Circuit in Ladder Logic

To create a start stop motor circuit in ladder logic, use a start pushbutton to set a latch coil that energizes the motor output, and a stop pushbutton to reset it. The circuit uses a holding contact from the motor coil to keep the motor running after the start button is released.

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Syntax

The start stop motor circuit in ladder logic uses these elements:

Start pushbutton (Normally Open contact): Initiates motor start.
Stop pushbutton (Normally Closed contact): Stops the motor.
Motor coil (Output coil): Controls the motor.
Holding contact (Auxiliary contact): Connected in parallel with the start button to keep the motor running after start.

The basic ladder rung looks like this:

ladder_logic

----[ Stop ]----[ Start ]----+----( Motor )
                            |
                            +----[ Motor ]

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Example

This example shows a start stop motor circuit where pressing the start button energizes the motor coil, and the motor stays on until the stop button is pressed.

ladder_logic

(* Ladder Logic Start Stop Motor Circuit Example *)

// Rung 1
|----[ ] Stop PB (NC) ----[ ] Start PB (NO) ----+----( ) Motor Coil
|                                              |
|                                              +----[ ] Motor Coil (Holding Contact NO)

// Explanation:
// Stop PB is normally closed, so power flows unless pressed.
// Start PB is normally open, closes when pressed.
// Motor Coil output energizes the motor.
// Holding contact from Motor Coil keeps the circuit latched after Start PB is released.

Output

Motor coil energizes when Start PB is pressed and remains energized until Stop PB is pressed.

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Common Pitfalls

Common mistakes when creating a start stop motor circuit include:

Using a normally open contact for the stop button instead of normally closed, which prevents the motor from stopping.
Forgetting the holding contact from the motor coil, causing the motor to stop immediately after releasing the start button.
Wiring the holding contact in series instead of parallel with the start button, which breaks the latch.

ladder_logic

(* Wrong way: Stop button as NO contact *)
|----[ ] Stop PB (NO) ----[ ] Start PB (NO) ----( ) Motor Coil

(* Right way: Stop button as NC contact *)
|----[ ] Stop PB (NC) ----[ ] Start PB (NO) ----+----( ) Motor Coil
|                                              |
|                                              +----[ ] Motor Coil (Holding Contact NO)

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Quick Reference

Component	Type	Function
Start Pushbutton	Normally Open (NO)	Starts the motor when pressed
Stop Pushbutton	Normally Closed (NC)	Stops the motor when pressed
Motor Coil	Output Coil	Energizes the motor
Holding Contact	Auxiliary NO Contact	Keeps motor running after start button is released

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Key Takeaways

Use a normally closed stop button and normally open start button for correct control.

Include a holding contact from the motor coil in parallel with the start button to latch the motor on.

The stop button breaks the circuit to de-energize the motor coil and stop the motor.

Wiring the holding contact in parallel with the start button is essential for continuous motor operation.

Test the circuit to ensure the motor starts and stops as expected before applying to real hardware.