Safety and efficiency are key to successfully operating electrical systems, and electrical components called circuit breakers are key to achieving this goal. Circuit breakers have been widely used for nearly a century and are one of the most important fire safety tools in modern homes, buildings, and appliances. While the basic function of a circuit breaker is the same as a fuse, the advantage of a circuit breaker is that it does not need to be replaced in the event of an overcurrent, saving money and allowing for quick repairs.
Today, circuit breakers have become a standard electrical component used in a variety of industries, but the public does not know much or know exactly about them, so in this article, let’s take a look at some of the details, considerations, and how to choose a circuit breaker. Of course, before starting any electrical project, be sure to check the building codes and electrical codes in your area to obtain any necessary permits.
1. What is a circuit breaker?
Circuit breakers are important safety devices that limit the flow of excessive current, thus protecting our homes, workplaces, and other critical infrastructure from potential fire risks. They act as switches that can establish, transmit, and interrupt electrical current under normal conditions. They can also establish and transmit current for a predetermined duration, and when an electrical short circuit or overload occurs, they can alleviate the problem and reduce risks by interrupting the current.
There are many types of circuit breakers, with properties that vary according to voltage, mounting, external design, location, and switching mechanism to suit a particular application.
2. Circuit breaker type
There are many types of circuit breakers. The main reason is that their application scenarios are too wide, so different voltage ratings, mechanisms, dimensions, etc. are derived. In terms of interruption mechanism, the most common types of low-voltage circuit breakers are usually divided into two categories: MCCB (molded case circuit breaker) and MCB (miniature circuit breaker).
Low voltage circuit breakers are designed to be easy to maintain. They are usually easily disassembled for repair without the user having to disassemble the switchgear. Some of these components are automatic, allowing operators to remotely open and close them. These circuit breakers can also be used in DC applications. Because the internal arc of DC does not stop and start like AC, a different type of circuit breaker must be used within the equipment.
These professional terms may be difficult to remember at first, so the easiest way to distinguish between the two types of circuit breakers in our daily life is to remember these two points: MCCB is suitable for higher energy environments, such as commercial plants; while MCB is used in smaller environments with lower rated currents.
1) Molded Case Circuit Breakers (MCCBs)
MCCBs house all electrical components within a well-insulated molded case. They are durable, adaptable, and designed for use in a variety of environments. MCCBs use thermal-magnetic and electromagnetic systems to trip and interrupt the current, protecting against sudden short circuits, ground faults, and thermal overloads.
With frame sizes ranging from 250 to 2000 amps and rated currents as low as 75A, they are ideal for low-voltage environments. They can also be used in medium voltage applications such as industrial or commercial control panels and switchboards. For example, I have a friend who is a graphic overlay supplier. He has his own graphic overlay production plant. During production, his plant uses a lot of current. One time, he asked me which circuit breaker could best protect the safety of his equipment and workers. I recommended MCCB to him, and later he told me that MCCB not only keeps the current stable but also can automatically cut off the current the first time in dangerous situations.
MCCBs are available with rated currents up to 1000-2,500 amps, rated interrupting currents up to 200,00 amps (again depending on the series and brand), adjustable trip currents, and thermal or thermal-magnetic operation.
2) Miniature circuit breakers (MCBs)
MCBs are designed to protect circuits from damage due to overloads and short circuits. They protect equipment, are compact, and have a simple manual reset process after tripping, making them ideal for isolating electrical components in residential, industrial, and commercial applications. Similar to MCCBs, they also support thermal or thermal-magnetic operation.
However, they are rated for no more than 100 amps, usually 2 to 32 amps, and are almost always rated for low voltage current, and the trip current is usually not adjustable. Rated breaking current can be as high as 18,000 amps, of course, this also depends on the series and brand.
3. How to buy a circuit breaker?
There are several different criteria to consider when selecting a circuit breaker, including voltage, frequency, breaking capacity, and more.
1) Rated voltage
Before deciding which circuit breaker is best for your needs, you should estimate your power usage needs. It is important to choose a circuit breaker with enough voltage capacity to meet the end application. Generally speaking, low voltage circuit breakers are mainly used for residential and commercial purposes. Medium voltage circuit breakers are used in industrial environments, and high voltage circuit breakers are used in power grids. Each type of circuit breaker has different voltage limits.
2) Frequency
The frequency rating of a circuit breaker should match the frequency of the electrical system. A mismatch can result in inefficient operation and possibly damage to the circuit breaker or the system it protects. For example, using a circuit breaker rated for 50 Hz in a 60 Hz system may reduce the system’s power rating and shorten the life of the circuit breaker. A circuit breaker with a maximum current of 600 A is suitable for frequencies of 50-120 Hz. Components with frequencies exceeding 120 Hz will force the system to derate the circuit breaker. As a rule of thumb, the higher the ampere rating in a particular frame size, the greater the required derating.
3) Maximum breaking capacity
The interrupting rating is generally considered to be the maximum amount of fault current that a circuit breaker can interrupt without causing a fault in the system itself. The maximum amount of fault current that a system can deliver can be calculated at any time. One absolute rule that must be followed when using the correct circuit breaker is that the circuit breaker’s interrupting capacity must be equal to or greater than the amount of fault current that can be delivered at the point in the system where the circuit breaker is used. Failure to apply the correct interrupting capacity will result in damage to the circuit breaker. An 80% rated circuit breaker is usually the best choice in this case.
4) Environmental capabilities
The efficiency of different circuit breakers is also related to the environment. These environments may include corrosion and humidity, high shock, high altitude, extreme weather (extreme heat and extreme cold), etc. In short, we need to try to buy the right circuit breaker for the location according to different environments. Here, I will give a few examples to explain the importance of environmental factors in detail:
- High Ambient Temperatures
In temperatures exceeding 104° F, a standard thermal-magnetic circuit breaker must be derated or recalibrated.
- Corrosion and Moisture
In humid environments, it is recommended that the circuit breaker be treated with special moisture treatment. This treatment helps to resist mold and/or fungus that can corrode the equipment. In environments where high humidity is prevalent, the best solution is to use a space heater in the enclosure.
- Altitude
At altitudes above 6,000 feet, circuit breakers must be rated for current carrying capacity, voltage, and interrupting capacity. Higher altitudes have thinner air, which cannot conduct heat away from current-carrying components as effectively as lower altitudes have denser air.
5) Equipment qualification test
When choosing a circuit breaker, in order to fully guarantee the quality, customers are advised to purchase circuit breakers that have been tested by UL (Underwriters Laboratories). Products that have not been tested by UL cannot guarantee the correct calibration of the circuit breaker. All UL-certified low-voltage molded case circuit breakers are tested according to UL Standard 489, which is divided into two categories: factory testing and field testing.
- UL Factory Testing: All UL-listed molded case circuit breakers undergo extensive production and calibration testing in accordance with UL Standard 489. UL listed circuit breakers contain a factory-sealed calibration system. An intact seal ensures that the circuit breaker is properly calibrated, has not been tampered with or altered, and that the product will operate in accordance with UL specifications. If the seal is broken, the UL guarantee and any warranty will be void.
- Field Testing: It is normal for data obtained in the field to differ from published information. Many users are confused as to whether the field data is flawed or whether the published information is out of sync with their specific model. The difference in data is that the factory testing conditions are very different from the field testing conditions. The purpose of factory testing is to produce consistent results. Test equipment designed specifically for the product being tested, as well as temperature, altitude, and climate-controlled environments, can affect results.
4. Conclusion
In summary, circuit breakers or power circuit breakers contribute to optimal electrical safety while also ensuring that any possible problems that may arise due to inevitable electrical problems are reduced (even if not completely alleviated). Therefore, before choosing a suitable circuit breaker, we should have a specific understanding of daily usage needs, electrical specifications, and applicable scenarios, and then choose the corresponding product type.
As technology develops, it becomes more important to install protective devices in circuits. It is also essential for users to understand the different types of circuit breakers and their applicability before choosing one. The practicality of electrical systems cannot be overemphasized.
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