The difference between the frame circuit breaker and the molded case circuit breaker

Simply put, it is the difference in size, not only the frame size of the circuit breaker is larger than the molded case circuit breaker, but also the frame circuit breaker’s current rating, segmentation capability, etc. must be greater than the molded case circuit breaker. This is an essential difference. Therefore, frame circuit breakers and molded case circuit breakers are used in different situations. Frames are applied to the upper line, and molded cases are applied to the lower level of the frame.

Molded case circuit breakers and frame circuit breakers are products that are commonly used in circuit breaker products. However, many people do not fully understand the difference between the two, and they often appear to be indecisive when purchasing. Some of the customers I faced also often have such problems. Therefore, based on this issue, I consulted three senior engineers in the factory and summarized some of their usual purchase experience. The difference between the two frame circuit breakers, as well as the need to pay attention when choosing.

Frame circuit breaker
Frame circuit breaker

Engineer No.1: Frame breaker has high segmentation capability and perfect function

The molded case circuit breaker adopts the plasticized structure, and the feature is that the circuit breaker shell and the frame are made of plastic, and the contacts and the arc extinguishing system are all placed in the insulation chamber to prevent the short circuit between the phases and ensure that the arc is ejected upward to ensure the contact. The system is reliably broken. The frame circuit breaker adopts a modular structure and is divided into frames, contact arc extinguishing systems, manual operation mechanisms, electric operating mechanisms, intelligent controllers, and drawer seats. Each part has become a complete and independent part. It can be fixed with only 1-2 screws during assembly, and disassembly is very convenient for maintenance.

Molded Case Circuit Breakers have a wide variety of products. Their features are compact structure, easy operation, and simple functions. Over current release and instantaneous release are generally configured. Frame circuit breakers are perfect, especially in recent years. Frame circuit breakers are moving towards high performance, easy maintenance, and networking.

In the rated current, the molded case circuit breaker is generally 630A (some new products can reach 1600A), and the rated current of the frame circuit breaker is much larger, generally 630A-6300A (such as our company’s DW15, DW16 and DW17 series Frame circuit breakers have reached this standard). In addition, in the segmentation capability, the frame circuit breaker is higher than the molded case circuit breaker.

In practical applications, circuit loops with a capacity of 800 A or more, or loops requiring a high degree of segmentation capability, or loops requiring more functions, should be frame circuit breakers, and loops below 630 A should be used. Molded case circuit breakers are generally used.

Engineer No.2: Molded case circuit breaker is suitable for branch circuit protection switch

molded case circuit breaker
molded case circuit breaker

All parts of the frame circuit breaker are installed in an insulated metal frame, often open type, and can be installed with a variety of accessories. It is more convenient to replace the contacts and parts, and it is mostly used in the main switch of the power supply. Over-current releases include electromagnetic, electronic, and intelligent trip units. The circuit breaker has four stages of long delay, short delay, instantaneous and ground fault protection, and each protection setting value is adjusted within a certain range according to its shell level. Both manual and electric operation are available. With the development of microelectronics technology, some intelligent circuit breakers currently have a regional selection chain function, which fully guarantees the sensitivity and selectivity of the operation.

Molded Case Circuit Breaker is a grounding terminal terminal contact, arc extinguishing chamber, release device and operating mechanism are all installed in a plastic casing, generally do not consider maintenance, suitable for branch circuit protection switch, over-current release device There are two kinds of electromagnetic and electronic, general electromagnetic molded case circuit breaker is a non-selective circuit breaker, only the long delay and instantaneous two protection methods, electronic molded case circuit breaker has a long delay, short delay, Instantaneous and ground fault four protection functions. Some of the new electronic molded case circuit breaker products also feature regional selective chaining. Most molded case circuit breakers are manually operated and some are also motor operated.

Engineer No.3: Frame Circuit Breakers Used as Main Switch of Distribution System

Frame circuit breakers are also generally referred to as open circuit breakers or universal circuit breakers. They are operated by hand, non-manually operated, energy storage type, non-energy storage type and electric type. According to the installation mode, it can be divided into two types: fixed type and drawer type. The fixed type outer shell is made of metal materials, and the outer dimensions are larger and the protection level is lower. Drawer type is made of engineering plastic shell, the structure is more compact, high protection level, easy maintenance. According to the protection characteristics, frame circuit breakers can be divided into non-selective (Type A) and selective (Type B), and Type B circuit breakers often use electronic over-current release, with long delay, short delay and instantaneous Action protection three-stage protection features. Intelligent frame circuit breaker built-in single-chip microcomputer, with display, alarm, self-test and communication functions, can be composed of IPC monitoring system. The biggest features of the frame circuit breaker are large capacity, high breaking capacity and enough short-time withstand current. For example, the rated current of the DW17 circuit breaker is up to 5000A, and the rated short-time withstand current is up to 100KA, which makes the frame circuit breaker very Good selectivity and stability.

It is precisely because of these excellent features that the price of the frame circuit breaker is higher, and it is mainly used for the main switch of the voltage distribution system, and the protection of main trunk lines and large motors with important loads.

Molded case circuit breakers are also referred to as device type circuit breakers. All parts are sealed in a housing. The auxiliary rough point, under voltage release, and shunt release are more modular. Because of its very compact structure, molded case circuit breakers cannot be overhauled. Many of them use manual operation, large-capacity optional electric split. Due to the application of electronic over-current release, molded case circuit breakers can also be divided into two types: Class A and Class B. Class B has good three-stage protection characteristics, but due to price factors, the use of electromagnetic release A The market share of products is higher.

Molded case circuit breakers are characterized by small size, good contact protection, easy installation and use, and low price. However, compared with the frame circuit breaker, its capacity is small, the short-circuit segmentation ability is low, the selectivity and tolerance are poor, and the intelligence is also slightly insufficient. Although in recent years, the capacity of new molded case circuit breakers has been very high, due to structural deficiencies, short-term withstand capability still cannot be significantly improved. This must be taken into consideration when selecting molded case circuit breakers.

These are the views of the three engineers on the two types of circuit breakers. I also talked a little bit about my own opinions. Of course, there are still big gaps compared with engineers. I think whether it is the choice of frame circuit breakers or molded case circuit breakers, mainly combined with their own circumstances, such as the ease of operation and maintenance, high breaking capacity, it is clear that the frame circuit breaker is more appropriate. And if it is used for the rated current is relatively low, while the budget is relatively low, the molded case circuit breaker is even more appropriate.

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