Simply put, the difference lies in size. Not only are frame circuit breakers larger than molded case circuit breakers in terms of overall dimensions, but frame circuit breakers also have larger current ratings and breaking capacities. This is a fundamental difference, hence frame circuit breakers and molded case circuit breakers are used in different applications: frame circuit breakers are used for upstream incoming lines, while molded case circuit breakers are used for downstream lines.
Molded case circuit breakers (MCCBs) and standard circuit breakers (SCCBs) are both commonly used circuit breaker products. However, many people are not fully aware of the differences between them and often hesitate when making a purchase decision. Some of my clients have also encountered this problem. Therefore, I consulted three senior engineers in the factory and summarized their purchasing experiences. Here, I will discuss the differences between MCCBs and SCCBs, as well as the points to consider when choosing between them. SCCBs offer higher sectionalizing capacity and more comprehensive functions - Engineer 1
Molded case circuit breakers utilize a plastic structure, characterized by the circuit breaker housing and frame being molded from plastic. The contacts and arc-extinguishing system are housed within insulating chambers to prevent phase-to-phase short circuits, ensure the arc propagates upwards, and guarantee reliable contact system disconnection. In contrast, frame circuit breakers employ a modular structure, comprising a frame, contact arc-extinguishing system, manual operating mechanism, electric operating mechanism, intelligent controller, and drawer base. Each part is a complete and independent component, requiring only one or two screws for assembly, making disassembly and maintenance very convenient.
Molded case circuit breakers come in a wide variety of types. They are characterized by their compact structure, ease of operation, and relatively simple functions. They are generally equipped with overcurrent trip units and instantaneous trip units. In contrast, frame circuit breakers have more complete functions. Especially in recent years, with the application of single-chip microcomputer technology, frame circuit breakers are developing towards high performance, easy maintenance, and networking.
In terms of rated current, molded case circuit breakers are generally below 630A (some new products can reach 1600A), while the rated current of frame circuit breakers is much higher, generally 630A-6300A (for example, our company's DW15, DW16, and DW17 series frame circuit breakers all meet this standard). Furthermore, frame circuit breakers have a higher breaking capacity than molded case circuit breakers.
In practical applications, circuits with a capacity of 800A or higher, circuits with particularly high sectionalizing capacity requirements, or circuits requiring multiple functions should use frame circuit breakers, while circuits with a capacity of 630A or lower generally use molded case circuit breakers. Molded case circuit breakers are suitable for use as branch circuit protection switches. - Engineer 2
All parts of a frame circuit breaker are housed within an insulated metal frame. It is typically an open type, allowing for the installation of various accessories and facilitating the replacement of contacts and components. It is commonly used as a main switch at the power supply end. Overcurrent trip units include electromagnetic, electronic, and intelligent types. The circuit breaker offers four protection stages: long-delay, short-delay, instantaneous, and ground fault. Each protection setting is adjustable within a certain range according to the frame rating. Both manual and electric operation are available. With the development of microelectronics technology, some intelligent circuit breakers now feature zone selection interlocking functions, ensuring both sensitivity and selectivity of operation.
A molded case circuit breaker (MCCB) houses the grounding terminal contacts, arc-extinguishing chamber, trip unit, and operating mechanism all within a single plastic casing. Generally, maintenance is not a primary concern, and it is suitable as a branch circuit protection switch. Overcurrent trip units are available in electromagnetic and electronic types. Electromagnetic MCCBs are typically non-selective, offering only long-delay and instantaneous protection modes. Electronic MCCBs offer four protection functions: long-delay, short-delay, instantaneous, and ground fault protection. Some newly released electronic MCCBs also feature area selective interlocking. Most MCCBs are manually operated, but some are motor-operated.
