How to determine whether the coil of an AC contactor is normal?

The following steps can be taken to determine whether the coil of an AC contactor is normal.

 Be sure to cut off the power during the operation to ensure safety:

### I. Visual Inspection

1. **Observe the Appearance of the Coil**

   - Check whether there are burnt black or charred marks on the surface of the coil, whether there 

is plastic melting and deformation, or any abnormal smell.

   - Check whether the wiring terminals are loose, oxidized, or burnt.

2. **Manual Pressing Test**

   - After cutting off the power, gently press the armature (movable iron core) with your finger to

 feel its flexibility. If there is severe sticking, it may be that the coil has not been fully attracted,

 resulting in long-term overload.

### II. Detection with a Multimeter

1. **Measure the Resistance of the Coil**

   - After cutting off the power, adjust the multimeter to the resistance range (such as ×1kΩ or ×100Ω).

   - Touch the test leads to the pins at both ends of the coil. Under normal circumstances, there should 

be a certain resistance value (the specific resistance value varies depending on the model. For example:

     - The resistance of a 220V coil is approximately 1kΩ to 5kΩ;

     - The resistance of a 380V coil is approximately 3kΩ to 10kΩ).

   - **Abnormal Situations**:

     - If the resistance is infinite → The coil is open-circuited and needs to be replaced.

     - If the resistance is significantly lower than the normal value → There is an inter-turn short circuit

 in the coil, and it needs to be replaced.

2. **Detect the Control Voltage**

   - After powering on (pay attention to safety), use the AC voltage range of the multimeter to measure 

the voltage across the two ends of the coil.

   - If the voltage is 0V → There is a fault in the control circuit (such as problems with buttons, wires, 

or fuses).

   - If the deviation of the voltage from the rated value exceeds ±10% → The voltage is abnormal, 

and the power supply needs to be adjusted.

### III. Power-on Test

1. **Observation during Short-term Power-on**

   - Ensure that the main circuit is powered off, and only power on the control circuit.

   - The contactor should quickly attract without obvious jamming or noise at the moment the coil is 

powered on.

   - **Abnormal Situations**:

     - If it does not attract → The coil may be open-circuited or the voltage may be insufficient.

     - If it releases immediately after attracting → There is an instantaneous power outage in the control 

circuit (such as poor contact of the contacts).

2. **Inspection of Coil Heating**

   - Cut off the power after powering on for 1 to 2 minutes and touch the surface of the coil with your 

hand.

   - If the temperature is obviously hot (exceeding 60°C) → There may be an inter-turn short circuit in 

the coil or the voltage may be too high.

### IV. Verification by Replacement Method

- **Replace the Coil with the Same Model**: If the fault still cannot be determined through the above 

steps, a new coil can be replaced for testing.

- **Replace the Contactor**: If the coil is normal but the contactor still does not work, there may be 

faults in the mechanical components or contacts.

### Precautions

1. **Safety First**: Be sure to cut off the power before operation to prevent electric shock or equipment 

damage.

2. **Model Matching**: When replacing the coil, select a model with the same voltage (such as 220V/380V)

 and power as the original coil.

3. **Professional Operation**: If you are not familiar with the circuit, it is recommended to have an electrician

 handle it to avoid misjudgment causing greater faults.

**Conclusion**: By means of visual inspection, resistance measurement, voltage testing, and verification by 

replacement, it is possible to quickly determine whether the coil is normal. If the coil has no faults, it is necessary

 to further troubleshoot the control circuit or mechanical problems.