What Is A Circuit Breaker? Overload Protection

By R.W. Hurst, Editor

What is a Circuit Breaker?

A circuit breaker (CB) is a crucial component in medium voltage power systems used in industrial, commercial, and institutional settings. As a safety mechanism, a circuit breaker is an electrical protective device designed to break the circuit and protect electrical systems from overloads, short circuits, and interrupting the flow of electrical faults by interrupting the flow of current. This article aims to provide an overview of medium voltage CBs to qualified electricians working in these environments.


Medium voltage circuit breakers are designed to handle voltage levels between 1 kV and 72.5 kV, making them suitable for various power distribution applications. As a result, they play a vital role in ensuring the safety and reliability of electrical systems in industrial, commercial, and institutional facilities. In addition, these breakers protect equipment from damage and minimize the risk of electrical fires and other hazards.

There are several types of medium voltage circuit breakers, each with unique characteristics and applications. Some common types include:


  • Air Circuit Breakers (ACB): ACBs use air as the arc extinguishing medium and are often found in indoor switchgear assemblies. They provide reliable protection for low and medium voltage circuits in industrial and commercial settings.
  • Vacuum Circuit Breakers (VCB): VCBs employ a vacuum interrupter to extinguish the arc, resulting in a faster and more efficient current interruption. They are widely used in medium voltage power systems due to their compact size, low maintenance, and high reliability.
  • Gas-Insulated Circuit Breakers (GCB): GCBs use an insulating gas, typically sulfur hexafluoride (SF6), to quench the arc. These breakers offer excellent insulation properties and high interruption capabilities, making them suitable for high voltage power systems.
  • Oil Circuit Breakers (OCB): OCBs rely on insulating oil as the arc extinguishing medium and insulation. Although newer technologies have largely replaced them due to environmental concerns and maintenance requirements, some older installations may still use them.


When selecting a medium voltage CB for a specific application, electricians must consider factors such as the breaker's voltage and current ratings, interrupting capacity, and response time. It's also essential to comply with local electrical codes and industry standards.

In industrial, commercial, and institutional power systems, CBs can be operated manually or automatically through protective relays. Protective relays monitor system parameters such as voltage, current, and frequency and send trip signals to the CB when a fault is detected. This automated response helps minimize the impact of electrical faults on equipment and overall system stability.

Maintenance of medium voltage CBs is crucial for ensuring their reliability and longevity. Regular inspection and testing can help detect potential issues before they escalate, reducing the risk of equipment damage and costly downtime. Some common maintenance tasks include:


  • Visual inspection: Check for signs of wear, damage, or corrosion on the breaker's exterior and connections.
  • Mechanical inspection: Examine the breaker's moving parts, such as contacts and operating mechanisms, for wear and proper alignment.
  • Electrical testing: Perform tests like insulation resistance, contact resistance, and timing tests to assess the breaker's electrical performance.
  • Cleaning and lubrication: Clean and lubricate moving parts as needed to prevent friction and ensure smooth operation.
  • SF6 gas analysis (for GCBs): Regularly monitor the gas's purity, moisture content, and pressure to ensure optimal performance.


Medium voltage circuit breakers play a vital role in protecting electrical systems in industrial, commercial, and institutional power systems. By understanding the various types of CBs and their applications, electricians can select the most suitable option for each application. In addition, regular maintenance, adherence to industry standards, and a focus on safety can help ensure these critical components' continued reliability and efficiency in power systems.

Furthermore, staying up-to-date with advancements in circuit breaker technology and industry best practices can help electricians improve the safety, efficiency, and reliability of the power systems they work with. For instance, new developments in solid-state CBs and advanced protective relay technologies can offer enhanced protection and faster fault detection and response.

In addition to selecting and maintaining the appropriate CBs, electricians should also consider implementing proper system design to mesh with the design of a circuit breaker and coordination between the two. Properly coordinating the settings of multiple circuit breakers and protective devices within a power system ensures that only the affected portion of the system is isolated during a fault, minimizing disruptions and downtime.

Training and safety protocols are crucial when working with medium voltage CBs in industrial, commercial, and institutional settings. Electricians should be knowledgeable about the specific equipment they work with and follow safety guidelines, such as lockout/tagout procedures and the use of personal protective equipment (PPE).

It is essential for qualified electricians working with the medium voltage power source in industrial, commercial, and institutional environments to understand what a CB is and how it functions. By selecting the right type of circuit breaker, performing regular maintenance, and adhering to safety guidelines, electricians can contribute to a safer and more reliable electrical infrastructure. In addition, keeping up with technological advancements and industry best practices can further enhance the performance and protection of these critical components in power systems.


How do I maximize the life of my circuit breaker?

To maximize the life of your circuit breaker, it's essential to follow proper installation, operation, and maintenance practices. Here are some tips to help extend the lifespan of your circuit breaker:

  • Choose the right circuit breaker: Select a circuit breaker with the appropriate voltage, current, and interrupting capacity ratings that match your electrical system's requirements. Also, ensure compatibility with the connected devices and compliance with local electrical codes and industry standards.
  • Proper installation: Ensure that the CB is installed correctly according to the manufacturer's guidelines and in compliance with local electrical codes. Proper installation helps prevent issues related to incorrect connections, poor contact, or misalignment.
  • Maintain a clean environment: Keep the area around the CB panel clean and free from dust, moisture, and corrosive chemicals. A clean environment reduces the chances of contamination, which can cause poor contact, reduced insulation, and other issues that could negatively affect the breaker's performance.
  • Regular inspection and maintenance: Conduct periodic visual inspections to check for signs of wear, damage, or corrosion on the breaker's exterior and connections. Regular maintenance tasks, such as cleaning and lubricating moving parts, can help prevent friction and ensure smooth operation. Additionally, perform electrical tests like insulation resistance, contact resistance, and timing tests to assess the breaker's performance and identify potential issues.
  • Avoid overloading: Prevent overloading the circuit by ensuring that the connected devices' total current draw does not exceed the CB's rated capacity. In addition, distribute loads evenly across circuits and avoid using too many high-power appliances on a single circuit.
  • Address tripping issues promptly: If CB trips frequently, investigate the cause and address the problem promptly. Frequent tripping could indicate an overloaded circuit, a short circuit, or a ground fault, which may require professional intervention to resolve.
  • Use appropriate accessories: Employ surge protectors, ground fault circuit interrupters (GFCIs), and other protective devices to shield the CB and connected equipment from voltage spikes, surges, and other electrical hazards.
  • Keep records: Maintain a log of maintenance, inspections, and performance tests to track the breaker's condition over time. This information can help identify trends and potential issues and determine when a CB may need replacement.
  • Follow manufacturer guidelines: Adhere to the manufacturer's recommendations for operation, maintenance, and replacement intervals. These guidelines are based on extensive testing and research and are designed to ensure the safe and reliable operation of the CB.

By following these best practices, you can maximize your CB's life, ensuring your electrical system's safety and reliability. Remember that working with electricity can be dangerous, and it's essential to consult a qualified electrician for any repairs, maintenance, or modifications to your electrical system.