Common faults of AC contactors and their solutions

### I. The contactor does not pull in

**Fault Phenomenon**: The contactor does not act after the coil is energized.

**Possible Causes**:

1. **Coil Fault**: The coil is open-circuited, burned out, or the voltage does not match.

2. **Control Circuit Problem**: The button contacts are oxidized, the auxiliary contacts have poor contact, 

the circuit is open-circuited, or the fuse is blown.

3. **Mechanical Blockage**: The iron core or moving contact is stuck by foreign objects.

**Solutions**:

- Use a multimeter to measure the resistance of the coil. If it is infinite, replace the coil.

- Check whether the voltage of the control circuit is normal, and clean the buttons and contacts.

- Disassemble the contactor, clean the internal foreign objects, or adjust the mechanical structure.

### II. Contact erosion or welding

**Fault Phenomenon**: The main contacts or auxiliary contacts are blackened and stuck together.

**Possible Causes**:

1. **Excessive Load Current**: Exceeding the rated capacity of the contacts, resulting in arc erosion.

2. **Failure of the Arc Extinguishing Device**: The arc extinguishing cover is damaged or not installed, 

and the arc cannot be extinguished.

3. **Frequent Start and Stop**: The contactor operates too frequently, increasing the wear of the contacts.

**Solutions**:

- Replace the contactor with a larger rated current, or install an arc extinguishing device.

- Clean the oxidized layer on the surface of the contacts. If it is serious, replace the contacts or the contactor.

- Reduce frequent operations and use a soft starter to control the motor instead.

### III. Abnormal noise of the contactor

**Fault Phenomenon**: It makes a "buzzing" sound or vibrates when pulling in.

**Possible Causes**:

1. **Incomplete Pull-in of the Iron Core**: The surface of the iron core has oil stains, dust, or rust.

2. **Damage to the Short-Circuit Ring**: The fracture of the short-circuit ring causes the iron core to vibrate.

3. **Too Low Voltage**: The voltage of the coil is insufficient, and the suction force of the iron core is not enough.

**Solutions**:

- Polish the contact surface of the iron core with sandpaper and clean the oil stains.

- Check whether the short-circuit ring is complete. If it is damaged, replace the iron core.

- Measure the control voltage to ensure it meets the rated value of the coil.

### IV. False operation or frequent tripping of the contactor

**Fault Phenomenon**: The contactor disconnects unexpectedly or repeatedly pulls in and disconnects.

**Possible Causes**:

1. **Unstable Control Circuit**: The button contacts have poor contact, the circuit is loosely connected, 

or there are interference signals.

2. **Load Overload**: A fault in the motor or load causes an excessive current, triggering the thermal relay protection.

3. **Auxiliary Contact Fault**: The self-locking contacts have poor contact and cannot maintain the pulled-in state.

**Solutions**:

- Check whether the connection of the control circuit is firm and replace the faulty buttons or relays.

- Troubleshoot the load fault and check whether the setting value of the thermal relay is appropriate.

- Clean or replace the auxiliary contacts.

### V. Overheating or burnout of the coil

**Fault Phenomenon**: The coil heats up severely or smokes.

**Possible Causes**:

1. **Abnormal Voltage**: The voltage is too high (burning out the coil) or too low (insufficient suction force

 causing the coil to have a continuous large current).

2. **Interturn Short Circuit of the Coil**: The insulation of the coil ages or gets damp.

3. **Blockage of the Iron Core**: The iron core is not fully pulled in, resulting in a long-term high current in the coil.

**Solutions**:

- Ensure that the control voltage is stable within the range of ±10% of the rated value.

- Replace the coil and check whether the mechanical part of the iron core is flexible.

- Improve the heat dissipation environment of the contactor and avoid humidity.

### VI. Damage to mechanical components

**Fault Phenomenon**: The moving contact moves slowly, the spring fails, or the components are deformed.

**Possible Causes**:

1. **Mechanical Wear**: Long-term use leads to a decrease in the elasticity of the spring and deformation 

of the contact support.

2. **Entry of Foreign Objects**: Dust, iron filings, etc. get stuck in the mechanical structure.

**Solutions**:

- Conduct regular maintenance and clean the internal foreign objects.

- Replace the worn springs, contacts, or mechanical components.

### Preventive Measures

1. **Regular Inspection**: Check the contact status, coil temperature, and mechanical flexibility every month.

2. **Cleaning and Maintenance**: Use dry compressed air to blow away the internal dust and avoid oil pollution.

3. **Voltage Monitoring**: Ensure that the voltage of the control power supply is stable and avoid large fluctuations.

4. **Load Matching**: Select a contactor with an appropriate capacity according to the load current.

5. **Arc Extinguishing Protection**: Install an arc extinguishing cover for contactors with a large capacity to

 avoid the harm of arcs.

**Reminder**: Be sure to disconnect the power supply before dealing with faults. It is recommended that 

non-professionals contact an electrician for operation to ensure safety.