Common Causes of MCB Failure and How to Prevent Them in Solar Systems

In solar systems, the Miniature Circuit Breaker (MCB) plays a vital role in ensuring the safety and proper functioning of the electrical circuits. However, MCBs are susceptible to failures that can compromise the performance of the entire solar system. Understanding the common causes of MCB failure and implementing preventive measures is essential for maintaining the reliability and efficiency of solar installations.

Understanding MCBs in Solar Systems

Before going into the causes of MCB failures, it’s better to know the role of MCBs in solar systems. An MCB acts as a protective device, designed to automatically disconnect the circuit in case of overload or short circuit. Thus, MCBs prevent potential hazards and safeguard the system against electrical faults.

Common Causes of MCB Failure

  • Short Circuits

Short circuits occur when a fault in the wiring creates a direct path for current to flow without resistance. This sudden increase in current can lead to malfunctioning of MCB, leading to failure. Short circuits can result from damaged wires, faulty connections, or equipment malfunction as visible from Figure 1.

-> Prevention

Conduct routine inspections of the wiring and connections in the solar system. Implement proper insulation measures and install circuit protection devices to decrease the risk of short circuits. Implement insulation measures to decrease the risk of short circuits. Make sure that insulation resistance (RINS) must be greater than the minimum required resistance (RMIN).

  • Issues Regarding Panel

A common issue engineers face in solar systems is related to the conductors of solar panels, which are the parts that carry the electricity generated by the panels. If these conductors are damaged, not properly installed, or don’t meet the required standards, it can disrupt the flow of electricity. When this happens, it can trigger the circuit breaker to shut off the power to prevent any electrical issues.

-> Prevention

To prevent this problem, it’s essential to ensure that the conductors of your solar panels are in good condition and correctly installed. Regular inspections can help detect any damage or issues early. Additionally, using high-quality, well-maintained solar panels can also help avoid this kind of trouble. Old or low-quality panels are more likely to cause disruptions in the electrical flow, which can lead to the circuit breaker tripping. So, investing in good-quality panels and keeping them well-maintained is necessary to prevent this common cause of MCB failure in solar systems.

  • Overloading

One of the primary reasons for MCB failure is overloading. When the current flowing through the circuit exceeds the MCB’s rated capacity, it can lead to overheating and, eventually, failure. This mostly results from variations in sunlight intensity affecting the power generation and ultimately causing overloads.

Ensuring MCBs are rated appropriately for expected loads is necessary for optimal system functioning and unforeseen stoppages. Simply, compare your actual load with the rated load of MCB and you are good to go with the MCB passing this specific test.

-> Prevention

Ensure that the MCBs in the solar system are appropriately rated for the expected loads. Regularly monitor the power output of the solar panels and adjust the system capacity accordingly.

  • Performance Degradation

Over time, MCBs can experience a decline in performance. Aging MCBs may become less responsive or fail to trip when necessary. The internal mechanisms can degrade, impacting the overall reliability of the MCB.

-> Prevention

Implement a regular maintenance schedule that includes the inspection and replacement of MCBs after achieving their running hours. Consider upgrading MCBs if they have been in use for an extended period.

Implement a regular maintenance routine for specific inspections and replacement of MCBs when they have achieved their desired life. The remaining life of equipment can be calculated using the formula:

  • Inverter-Related Challenges

Another significant problem leading to MCB failure results from the inverter issue. One major cause of inverter malfunctions is the occurrence of higher AC voltage levels. When the AC voltage exceeds safe levels, it can lead to over-voltage conditions, potentially tripping the solar panel and affecting the performance of the entire system.

-> Prevention

To prevent inverter problems due to over-voltage, it’s essential to monitor and maintain the AC voltage within the recommended range. Regularly check the voltage levels in the solar system and ensure that the inverter is equipped with appropriate protective features to handle voltage fluctuations. Investing in quality inverters with built-in voltage regulation and surge protection mechanisms can significantly reduce the risk of inverter-related issues, ultimately contributing to the overall reliability of the solar system.

  • Environmental Factors

Solar system equipment is often exposed to diverse environmental conditions, including temperature variations, humidity, and even dust. These factors can contribute to the damage of MCB components, affecting their performance. As we can in figure 2 below.

-> Prevention

Protect MCBs from direct exposure to harsh weather conditions. Install protective shields to minimize the impact of environmental factors on the components.

  • Manufacturing Defects

In some cases, MCB failures can be attributed to manufacturing defects. These defects may not be immediately apparent and come to light over time, leading to malfunctions.

-> Prevention

Source MCBs from reputable manufacturers with a track record of quality. Implement thorough testing of new MCBs before installing them into the solar system.

A reliability assurance test is also a quantitative analysis that gives you an overview of the MCB’s credibility. Reliability assurance index (I) is a term used to check the quality of MCBs sourced from any buyer.

  • Improper Installation

Incorrect installation practices, such as loose connections or inadequate mounting, can contribute to MCB failures. Poor installation can compromise the effectiveness of the MCB in detecting and responding to electrical faults.

-> Prevention

Ensure that MCBs are installed according to the manufacturer’s guidelines and industry standards. Tighten connections securely, and regularly inspect for any signs of improper mounting or wiring.


The reliability of MCBs is integral to the overall performance and safety of solar systems. Regular inspections, proper load management, and adherence to installation standards are key aspects of preventing MCB failures. By understanding the common causes of MCB failure and implementing preventive measures, solar system operators and engineers can significantly enhance the life of components and in turn the efficiency of solar systems.


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