how to troubleshoot a mitsubishi magnetic contactor for ac motor



Magnetic contactors are vital components in AC motor control systems. They serve as an interface between control circuits and load circuits, allowing for effective control and protection of motors. Among the various manufacturers of magnetic contactors, Mitsubishi Electric has earned a solid reputation for producing high-quality and reliable products. Nevertheless, even the most robust devices can encounter issues, requiring troubleshooting to ensure smooth operation. In this article, we will delve into the intricacies of troubleshooting a Mitsubishi magnetic contactor for an AC motor. We will explore common problems, their causes, and provide practical solutions to get your motor up and running again.

Understanding Magnetic Contactors

Magnetic contactors are electromechanical devices designed to control the flow of electric current to an AC motor. They consist of two main components: a coil and a set of contacts. The coil is an electromagnetic component responsible for attracting the contacts and closing the electrical circuit. The contacts, on the other hand, are responsible for carrying the load current to the motor.

Common Problems and Troubleshooting Solutions

1. Motor Fails to Start

When your AC motor fails to start, it can be a frustrating experience. Several factors could contribute to this issue. One common cause is a fault in the contactor's coil. If the coil fails, it will not create the necessary magnetic field to close the contacts and supply power to the motor.

To troubleshoot this problem, start by checking the coil's electrical connections. Ensure that the coil is receiving the proper voltage by using a multimeter. If the voltage is within the specified range, but the coil still fails to energize, it may be necessary to replace the coil. Refer to your contactor's documentation or consult a professional to find a suitable replacement.

2. Motor Stops Abruptly

If your motor stops abruptly during operation, it can be a cause for concern. One potential explanation for this behavior is a faulty contactor overload relay. The overload relay is responsible for protecting the motor from excessive current and preventing overheating.

To troubleshoot this issue, first, check the overload relay settings. Ensure that they are correctly adjusted to match the motor's rated current. If the settings are correct, measure the current flowing through the motor using a clamp meter. If the measured current exceeds the relay's threshold, it indicates an overload condition. In this case, you might need to replace the overload relay with a new one suitable for your motor's requirements.

3. Contactor Fails to Close

Occasionally, you may encounter a situation where the contactor fails to close when the control circuit activates it. This malfunction can occur due to various reasons, including a damaged or worn-out contactor coil, a stuck contact, or a power supply issue.

To troubleshoot this problem, begin by inspecting the contactor coil for any visible damage or signs of wear. If the coil appears to be in good condition, check the contacts for any debris or obstructions that might be preventing them from closing properly. Cleaning the contacts or replacing them if necessary can often resolve this issue. Additionally, ensure the contactor is receiving the correct power supply voltage and that all connections are secure.

4. Contact Welding

Contact welding is a problem characterized by the sticking of contacts due to an excessive current flow or a faulty contactor design. When contacts weld together, they can no longer open or close as required, leading to issues with motor control and circuit protection.

To troubleshoot this problem, start by examining the contacts for any signs of welding or damage. If contacts appear welded or fused, you will need to replace the contactor with a new one. To prevent future welding issues, consider using contactors with larger contact ratings or those specifically designed to handle higher current loads.

5. Noisy Operation

Unusual noises during the operation of a magnetic contactor can indicate potential problems. Common causes of noisy operation include loose internal components, improper mounting, or even age-related wear and tear.

To troubleshoot this issue, first, check all screws and mounting hardware to ensure they are tightened properly. Loose screws can cause vibrations and contribute to noisy operation. If the noise persists, it may be necessary to replace the contactor if it is old or shows signs of wear. Proper maintenance and regular inspection can help prevent noisy operation in the future.


In conclusion, troubleshooting a Mitsubishi magnetic contactor for an AC motor involves identifying common problems and implementing appropriate solutions. Ensuring that the coil receives the correct voltage, adjusting overload relay settings, and cleaning or replacing contacts can resolve various issues. Contact welding and noisy operation may necessitate the replacement of the contactor itself. By understanding these troubleshooting techniques, you can maintain the optimal functioning of your AC motor control system and prevent any potential disruptions. Remember, when in doubt, consult the contactor's documentation or seek professional assistance.


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