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The difference between MCB, molded case and frame circuit breaker

By:Nader Updated:September 09,2020 12:08PM

Friends who have been in contact with circuit breakers know that even if you just go to a hardware store to buy a switch, I am afraid you are familiar with the terms miniature circuit breaker, air switch, molded case circuit breaker, and frame circuit breaker. So what do these nouns mean? Is there any connection between them?

Circuit breaker

Circuit breaker is a collective term for all the above terms. Circuit breaker refers to a mechanical switch that can connect, carry and break the current in the circuit. Note that there are two biggest characteristics of the circuit breaker, one is that it can cut off the current, and the other is the internal arc extinguishing device. Some switches, such as knife switches, can not be called circuit breakers without arc extinguishing devices although they can cut off the current.

There are many basis for the classification of circuit breakers. Among them, the most widely mentioned is based on the insulation medium and current classification. According to the insulating medium, it can be divided into air circuit breakers and vacuum circuit breakers; according to the current, it can be divided into miniature circuit breakers, plastic case circuit breakers and frame type (universal) circuit breakers.

Air switch

The abbreviation of air switch, also called air circuit breaker. The opposite is a vacuum circuit breaker.

The difference between the two is that the arc extinguishing device of the air circuit breaker relies on the elongated arc (the arc is the electric spark), and then relies on air cooling for arc extinguishing. The vacuum circuit breaker relies on the internal vacuum bubble to extinguish the arc.

Vacuum circuit breaker

Which is better, I'm afraid you will know the names of the two. Because the internal structure of the air circuit breaker is in contact with the air for a long time, and the arc extinguishing device has a complicated structure, it is susceptible to the influence of temperature, humidity and air erosion. The internal structure of the vacuum circuit breaker is simple and completely isolated from the air, so the failure rate and service life are better than those of the air circuit breaker. Of course, the price of vacuum circuit breakers is also very considerable.

We usually use air switches every day, so the term "air switch" is often heard, and many ordinary users don't even know the term "virtual air switch".

Miniature circuit breakers, molded case circuit breakers, frame circuit breakers

According to the current points, it can be divided into miniature circuit breakers, molded case circuit breakers (plastic case circuit breakers) and frame circuit breakers (universal circuit breakers). Note that these three belong to the category of low-voltage circuit breakers.

Miniature circuit breaker, current does not exceed 63A. Molded case circuit breaker, the current does not exceed 600A. Frame circuit breaker, the current does not exceed 4000A.

Due to the different sizes of current that can pass, correspondingly, the size of the internal structure is also different, resulting in correspondingly larger or smaller external dimensions.

In addition, there are many changes in the opening and closing operation methods. Generally, the operation modes of miniature circuit breakers and molded case circuit breakers are relatively monotonous. However, due to the large size of the frame circuit breaker, it is difficult to open and close the circuit breaker by simple mechanical operation. Therefore, various operation methods such as electromagnet, electric operation and handle are introduced.