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Molded case circuit breaker test
Molded case circuit breaker testing
Resource: https://youtu.be/t5GPHFzjFK0

Molded case circuit breaker testing, when combined with proper maintenance practices, can help ensure an MCCB’s longevity and reliability. This MCCB testing and maintenance guide details the various tests, how to perform them, and how to maintain MCCB circuit breakers for maximum performance.

Molded Case Circuit Breaker Testing

Molded case circuit breaker testing means carrying out essential breaker inspections to ensure its safe operation. They’re usually part of an electrical system’s routine maintenance. Electricians will usually perform these tests on new or existing circuit breakers.


Electricians may perform various test procedures on molded case circuit breakers as part of their preventive maintenance. The following MCCB test types are the most important:

  • Insulation Resistance Test: The insulation resistance test is used to determine the insulation integrity of a molded case circuit breaker.
  • Overcurrent Protection Test: This subjects the breaker to an overload current (about 3 times its rated current) to determine its tripping performance.
  • Contact Resistance Test: This test is used to determine the integrity of the contacts and the breaker’s ability to respond to a fault.

MCCB Testing Procedure

Molded case circuit breaker testing involves the use of different electrical testing instruments, such as insulation resistance tester. These tests also require knowledge of the appropriate electrical readings. Here is how to test MCCB circuit breakers for each of the mentioned parameters.

  • Insulation resistance test requires the use of an insulation resistance-tester. Start by testing the resistance between the phases then between the line and load. A resistance greater than 50 mega ohms must be registered.
  • For contact resistance, a digital ohmmeter is used. An above 50% deviation should cause alarm, and require the breaker to be tested further.
  • When testing for overcurrent protection, a high current of around 3 times that of the specific MCCB’s rated continuous current is applied. To test the instantaneous mechanism, apply short current pulses and increase the magnitude until the breaker trips.
Molded case circuit breaker installation
Molded case circuit breaker installation
Resource: https://youtu.be/nGSIosGIQY0

Molded Case Circuit Breaker Maintenance

In addition to the recommended molded case circuit breaker testing procedures, it’s good practice to also follow some basic maintenance practices. These include regular cleaning, inspecting for signs of damage or wear, and lubricating any moving parts.

  • MCCB Inspection: check that all MCCB wiring connections are secure and free of corrosion. Also, look for any signs of arcing or overheating (which may indicate breaker problems), bent or broken linkages, and compromised insulation.
  • MCCB Cleaning: Regularly inspect and clean any dust or debris from the case of the MCCB to help ensure proper operation. Dirt can also build up on the internal components, so it’s important that you clean them too.
  • MCCB Lubrication: Apply lubricant to any moving parts or linkages in order to keep them operating smoothly. Ensure, that you’re using the correct lubricant for your breaker, and do not over-lubricate.

Note that some molded circuit breaker cases come sealed for life and should not be opened or serviced. If that’s the case, only the breaker outside and terminals can be cleaned or maintained using any other way.

These molded case circuit breaker maintenance activities ensure that it is functioning properly and can provide reliable protection to the electrical system. It translates to a business that runs without any interruptions and minimizes the risk of any safety hazards.

Testing a failed molded case circuit breaker, MCCB
Testing a failed molded case circuit breaker, MCCB
Resource: https://youtu.be/6VE5chKMFuo

Molded Case Circuit Breaker Life Expectancy

The lifespan of a breaker depends on the quality and condition of the components. If properly maintained, it should be able to operate for many years without major issues. Use these tips to prolong the molded case circuit breaker life expectancy.

1. Ensure timely maintenance activities. When neglected, your MCCB can suffer from earlier-than-expected wear and tear, subjecting you to expensive and unnecessary replacements.

2. Regularly check the MCCB parts for any signs of wear, arcing or overheating. These indicate issues within the breaker and its operation. Correct them if possible.

3. Make sure that the molded case breaker is being used within its rated capacity to avoid overloading it. Currents higher than the manufacturer-rated values can quickly cause irreversible damage.

4. Regularly test the MCCB as specified by the manufacturer in order to ensure proper operation and timely detection of any issues. Molded case circuit breaker manufacturers usually include these in the manual.

5. Keep any dirt or debris away from the breaker to ensure proper operation. Dirt can slow down moving breaker parts or overheating at by increasing contact resistance. Clean them when necessary.

6. Ensure that all wiring is secure and free of corrosion for optimal performance. Do so by periodically inspecting the breaker and its connections.

By following these molded case circuit breaker maintenance guidelines, you can ensure its longevity and keep it operating safely within its rated capacity. Additionally, it is important to use quality components from reputable manufacturers to maximize the breaker’s lifespan.

Molded Case Circuit Breaker Lockout Devices

As part of ensuring protection breakers remain secure and work as intended, safety lockout devices are often used. These lock the breakers so they cannot accidentally be reset or switched on/off by unauthorized personnel.

Molded case circuit breaker lockout devices are typically mounted to the breaker’s handle, preventing it from being operated until the device is removed with a key (which is held by authorized personnel only).

MCCB lockout devices are available in different styles and fit different types and sizes of breakers. Therefore, ensure that you select the correct size and type for your MCCB when ordering. This video shows how to effectively install one type of these devices on an MCCB breaker.


In conclusion, it’s important to remember the importance of molded case circuit breaker testing and maintenance. Tests confirm that the breaker is functioning correctly and can provide reliable protection, while basic maintenance helps to ensure that it will continue to work for its entire life cycle.

IGOYE Molded Case Circuit Breaker Catalog
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