Principle and Wiring Guide for the Start-Hold-Stop Circuit (Self-Locking Circuit)

The start-hold-stop circuit is the most fundamental self-locking control circuit in industrial electrical control. Its core function is to trigger equipment operation via a start button, cut off operation via a stop button, and enable the equipment to keep running even after the start button is released. It is widely used in the standalone control of devices such as motors, pompes, and fans. Combined with the previously mentioned Schneider LC1E180M5N contactor, this document provides a complete circuit design, wiring, and commissioning solution.

1. Composition of Core Components

Taking three-phase motor control as an example, the start-hold-stop circuit needs to be equipped with the following components:

1. Principe de fonctionnement
2. Core Logic

Start and Self-Locking: Press the start button → the contactor coil is energized → the main contacts close and the motor runs; at the same time, the contactor auxiliary normally open contacts close, replacing the start button to keep the coil energized (self-locking), so the motor continues to run after the start button is released.

Stop and Unlocking: Press the stop button → the coil circuit is disconnected → the main contacts and auxiliary normally open contacts open simultaneously, the motor stops, and the self-locking is released; the motor can only restart by pressing the start button again.

2. Protection Logic

Protection contre les courts-circuits: When the current in the main circuit is excessively high, the air circuit breaker trips instantaneously.

Protection contre les surcharges: When the motor is overloaded, the normally closed contacts of the thermal overload relay open, cutting off the coil circuit, the contactor releases, and the motor shuts down.

III. Étapes de câblage (Taking LC1E180M5N Contactor as an Example)

1. Câblage du circuit principal (Three-Phase High-Voltage Circuit)

The main circuit is responsible for supplying power to the motor. Wiring sequence: Power Supply → Circuit Breaker → Contactor Main Contacts → Thermal Overload Relay → Motor

2. Control Circuit Wiring (220V AC Low-Voltage Circuit)

The control circuit is responsible for controlling the on-off of the contactor coil. The coil voltage is 220V AC (coil parameter of LC1E180M5N). Wiring sequence: Control Power Supply → Stop Button → Start Button → Thermal Overload Relay Normally Closed Contacts → Contactor Coil → Self-Locking Contacts → Power Supply Neutral Line

Specific Wiring Steps

1. Take one phase of live wire (par ex., L1) and neutral line N from the three-phase power supply as the control circuit power supply (220V et).
2. Connect the live wire end to one end of the stop button’s normally closed contact (Caroline du Nord), and connect the other end of the stop button to one end of the start button’s normally open contact (NON).
3. Connect the other end of the start button to one end of the thermal overload relay’s normally closed contact, and connect the other end of the thermal overload relay’s normally closed contact to the contactor coil terminal A1.
4. Connect the contactor auxiliary normally open contacts (par ex., 13-14) in parallel across the start button terminals (to achieve self-locking): connect auxiliary normally open contact 13 to the common terminal of the stop button and start button, and connect contact 14 to the common terminal of the thermal overload relay normally closed contact and A1.
5. Connect the contactor coil terminal A2 to the power supply neutral line N.
6. Safety Precautions
7. Power-Off Operation: Before wiring, must disconnect the power supply of the main circuit and control circuit, and use a test pencil to confirm no voltage exists.
8. Button Selection: The stop button must adopt normally closed contacts, and priority should be given to red mushroom-head buttons (emergency stop), which should be installed in an easily accessible position.
9. Self-Locking Contacts: Must use the contactor’s own auxiliary normally open contacts; it is prohibited to use other components as substitutes, otherwise self-locking cannot be achieved.
10. Wire Diameter Selection: The cross-sectional area of the control circuit wire should be ≥1.0mm²; the main circuit wire should be selected according to the motor current (par ex., select 4mm² copper core wire for an 18A motor).
11. Grounding Protection: The motor housing and contactor metal frame must be reliably grounded to prevent leakage and electric shock.
12. Commissioning Steps
13. Wiring Inspection

Check whether the phase sequence of the main circuit is correct, and whether the control circuit wiring conforms to the sequence of “Stop → Start → Thermal Overload Relay → Coil → Self-Locking”.

Use a multimeter to measure the control circuit: when the start button is pressed, there should be continuity between A1 and A2 (220V et); continuity should remain after releasing the button (self-locking is effective); the circuit should disconnect when the stop button is pressed.

2. No-Load Test (Disconnect Motor Wiring)

Close the circuit breaker; the power indicator light turns on.

Press the start button → the contactor pulls in (with a “cliquez” sound), the auxiliary contacts realize self-locking, and the contactor remains pulled in.

Press the stop button → the contactor releases, and the motor stops.

Simulate overload test: manually press the test button of the thermal overload relay → the contactor should release immediately.

3. Load Test

Connect the motor wiring properly and close the circuit breaker.

Press the start button; the motor starts smoothly without abnormal noise; it continues to run after releasing the button.

Press the stop button; the motor stops; it can start normally again.

1. Common Fault Troubleshooting