Metodo di cablaggio per il circuito di controllo autobloccante

The core principle of a self-locking control circuit (also called self-holding circuit) is to use the normally open auxiliary contact of a control component (contactor/intermediate relay) and connect it in parallel with the pulsante di avvio, so as to realize the function that the coil of the control component remains energized after the start button is released. Combined with common industrial scenarios, the structured wiring steps are provided below for two schemes: intermediate relay self-locking (suitable for Schneider RXM2LB2P7) and contactor self-locking (mainstream for motor control).

1. Core Principle

Press the start button (normalmente aperto) → the coil is energized → the normally open auxiliary contact closes → the auxiliary contact replaces the start button to conduct the circuit → release the start button, and the coil is still energized through the auxiliary contact (self-locking);

Press the stop button (normalmente chiuso) → the circuit is disconnected → the coil is de-energized → the auxiliary contact opens → self-locking is released.

1. Scheme 1: Self-Locking Control Circuit of Intermediate Relay (RXM2LB2P7)

Scenari applicativi

Control of low-power loads (such as indicator lights, solenoid valves, small pumps), signal transfer circuits. The coil voltage is adapted to 230V AC (coil parameter of RXM2LB2P7).

1. Component List

2. Wiring Steps (Based on RXM2LB2P7 Pin Definition)

RXM2LB2P7 is an 8-pin relay, and the pin functions are as follows:

– Coil Pins: Pin 1 (+), Pin 2 (-) (no positive-negative polarity distinction for 230V AC)

– Contact Pins: 3-4 (Normally Closed NC), 3-5 (Normally Open NO); 6-7 (Normally Closed NC), 6-8 (Normally Open NO) (2 sets of change-over contacts)

Wiring Process:

1. Power Supply Connection: Connect the live wire (l) of 230V AC to one end of the stop button, and connect the neutral wire (N) directly to Pin 2 of the relay coil.
2. Series Connection of Stop Button: Connect the other end of the stop button to one end of the start button + one end of the normally open auxiliary contact of the relay (select Pin 5 of 3-5 pins).
3. Parallel Connection of Start Button and Auxiliary Contact: Connect the other end of the start button to the other end of the normally open auxiliary contact of the relay (select Pin 3 of 3-5 pins).
4. Coil Circuit Closure: Connect the common terminal (Pin 3) after parallel connection to Pin 1 of the relay coil.
5. Load Circuit Wiring: Select another set of contacts (per esempio., 6-8 normalmente aperto), connect the live wire (l) to Pin 6, connect Pin 8 to one end of the load, and connect the other end of the load to the neutral wire (N).
6. Working Process

Start: Press the start button → Pins 1-2 of the coil are energized → Normally open contacts 3-5 E 6-8 close → The closure of contact 3-5 realizes self-locking → Contact 6-8 closes → The load is energized and works.

Stop: Press the stop button → The coil circuit is disconnected → The coil is de-energized → Contacts 3-5 E 6-8 reset and open → The load stops working, and self-locking is released.

III. Scheme 2: Contactor Self-Locking Control Circuit for Motor

Scenari applicativi

Start-stop control of three-phase asynchronous motors (most commonly used in industry). The coil voltage of the contactor must match the control power supply (per esempio., 220V AC/380V AC).

1. Component List

2. Wiring Steps

(1) Circuito di controllo (Low-Voltage Side, per esempio., 220V e)

1. Live wire (l) → Stop button (normalmente chiuso) → Start button (normalmente aperto) → One end of the contactor coil.
2. The normally open auxiliary contact of the contactor is connected in parallel at both ends of the start button (to realize self-locking).
3. The normally closed contact of the thermal overload relay is connected in series in the coil circuit (protezione da sovraccarico).
4. The other end of the contactor coil → Neutral wire (N).

(2) Circuito principale (High-Voltage Side, Three-Phase 380V AC)

1. Three-phase power supply → Circuit breaker → Main contact incoming terminals of the contactor (L1/L2/L3).
2. Main contact outgoing terminals of the contactor → Incoming terminals of the thermal overload relay → Outgoing terminals of the thermal overload relay → Three-phase terminals of the motor (U/V/W).
3. Working Process

Start: Press the start button → The contactor coil is energized → The main contacts close, and the motor is energized and runs; at the same time, the normally open auxiliary contacts close → Self-locking is achieved, and the motor continues to run after releasing the start button.

Stop: Press the stop button → The coil is de-energized → The main contacts and auxiliary contacts open → The motor stops.

Overload Protection: Motor overload → The thermal overload relay acts → The normally closed contact opens → The control circuit is powered off → The motor shuts down.

1. Key Wiring Precautions
2. Component Selection Matching

The coil voltage of the relay/contactor must be consistent with the control power supply (per esempio., RXM2LB2P7 is 230V AC, and cannot be connected to 24V DC).

The rated current of the contacts must be ≥ the load current to avoid contact ablation (the rated contact current of RXM2LB2P7 is 5A, and it cannot drive high-power motors).

2. Correct Button Type Selection

The start button must be normally open, and the stop button must be normally closed; if a normally open button is used as the stop button, it will cause failure to stop the equipment, posing a safety hazard.

3. Wiring Safety Specifications

Prima del cablaggio, disconnect all power supplies and use a test pen to confirm no electricity before operation.

The control circuit and main circuit shall be wired separately. The wire specification of the main circuit shall be selected according to the load current, and 0.5-1.5mm² wires can be used for the control circuit.

After wiring, check for short circuits and loose connections, measure the resistance of the coil circuit with a multimeter, and conduct a power-on test only after confirming no abnormalities.

4. Troubleshooting Points

When the start button is pressed, the coil is not energized: Check whether the power supply, stop button and start button are conducting.

The coil pulls in when the start button is pressed, but disconnects immediately after releasing: The self-locking auxiliary contact is not properly connected or is damaged.

The coil is energized but the load does not work: Check whether the load contact is damaged or the load itself is faulty.

1. Supplementary: Special Application of RXM2LB2P7 Self-Locking Circuit

If it is necessary to use RXM2LB2P7 to realize multi-channel self-locking control, its 2 sets of change-over contacts can be utilized:

– One set of contacts (3-5) serves as the self-locking auxiliary contact;

– The other set of contacts (6-8) controls the load circuit;

– If expansion is required, other relays/contactors can be controlled through the relay contacts.