how to test ac contactor coil



Testing the AC contactor coil is an essential step in ensuring the smooth operation and longevity of electrical equipment. The AC contactor is a crucial component in controlling the flow of electricity. Over time, wear and tear may affect the performance of the contactor coil, leading to various issues. By carrying out regular tests on the AC contactor coil, you can identify any potential problems and take proactive measures to avoid major breakdowns. In this article, we will guide you through the process of testing the AC contactor coil, ensuring that your electrical systems stay in optimal condition.

Different Types of AC Contactor Coils

There are various types of AC contactors available in the market, each with its specific coil design. It is essential to understand the different types to ensure that you test the right coil effectively.

1. Standard DC Coil

The standard DC coil is one of the most commonly used AC contactor coils. It operates on direct current (DC) and requires a power supply of a specified voltage. To test this type of coil, you would typically use a multimeter to measure the resistance across the coil terminals. By comparing the resistance value to the manufacturer's specifications, you can determine if the coil is functioning correctly.

2. Electronic Coil

Electronic AC contactor coils use electronic circuitry to control the flow of electricity. These coils are more efficient and require less power than standard DC coils. Testing electronic coils may require specialized tools, such as an oscilloscope, to analyze the electrical signals. This allows you to assess the functionality of the coil in more detail.

3. Interchangeable Coil

Interchangeable coils are designed to be easily replaceable, providing versatility in different applications. These coils often have specific voltage ratings that need to be considered during testing. To test an interchangeable coil, you would follow similar procedures as for a standard DC coil, ensuring that the voltage applied matches the coil's specifications.

Testing Equipment and Safety Precautions

Before you begin testing the AC contactor coil, it is crucial to have the right tools and take necessary safety precautions. Here are some essential items you will need:

1. Multimeter

A multimeter is a versatile tool used to measure voltage, current, and resistance. It is essential for testing the AC contactor coil's resistance and ensuring it falls within the acceptable range.

2. Oscilloscope

An oscilloscope is a more advanced testing tool that can help analyze the electrical signals produced by the AC contactor coil accurately. It provides detailed visual representations of the waveform, allowing for more in-depth analysis.

3. Insulated Gloves and Safety Glasses

When working with electrical components, it is vital to prioritize safety. Insulated gloves and safety glasses are essential in protecting yourself from any potential electrical hazards.

4. Discharge Circuit

Before conducting any tests on the AC contactor coil, it is crucial to ensure that the circuit is discharged. This prevents the risk of electrical shock and protects both you and the equipment.

Testing Procedure

Now that you have the necessary equipment and safety precautions in place, let's walk through the step-by-step testing procedure for the AC contactor coil:

1. Turn Off Power

Before conducting any tests, make sure to turn off the power supply and wait for the system to de-energize completely. This prevents any accidental electrical shocks during the testing process.

2. Disconnect the Control Wires

To access the AC contactor coil, you will need to disconnect the control wires connected to the coil. These control wires are typically smaller in size and can be detached easily using a screwdriver or pliers.

3. Measure the Resistance

Using a multimeter set to the resistance measuring function, carefully measure the resistance across the AC contactor coil terminals. Compare this resistance value with the manufacturer's specifications to determine if the coil is functioning within the acceptable range.

4. Analyze the Waveform (Optional)

If you have an oscilloscope, connect it to the AC contactor coil terminals to analyze the waveform. This allows for a more detailed assessment of the coil's functionality, detecting any irregularities or abnormalities in the electrical signals.

5. Check for Continuity

In addition to measuring resistance, it is essential to check for continuity across the AC contactor coil. Continuity testing ensures that the coil is not open or short-circuited, as this can significantly impact its performance. A multimeter can also be used for this test by setting it to the continuity mode.

6. Inspect for Physical Damage

While testing the AC contactor coil, take the time to visually inspect it for any signs of physical damage. Look for burnt or melted components, loose connections, or any other observable issues that may affect its performance.


Regular testing of the AC contactor coil is crucial in maintaining the effectiveness and reliability of electrical equipment. By following the testing procedure outlined in this article, you can identify any potential issues with the coil and take appropriate measures to address them. Remember to prioritize safety by following all necessary precautions and using the recommended testing equipment. By ensuring the proper functioning of the AC contactor coil, you can improve the overall efficiency and longevity of your electrical systems, minimizing costly downtime and repairs.


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