We all know MCCB, which is a type of terminal equipment that is wrapped in a plastic shell and has an internal connection network. It has a very low discharge resistance and can prevent equipment from being affected by moisture or dust in wet environments. The characteristic of this circuit breaker is its small size, small footprint, and the ability to release a large amount of current in a short period of time. In addition, MCCB also has the advantages of simple installation, low failure probability, and high reliability. ACB, on the other hand, is a mechanical switching device that can connect, carry, and break current under normal circuit conditions, as well as connect, carry, and break current for a certain period of time under specified abnormal circuit conditions. Mainly used for closing incoming lines, busbars, and other high current circuits in low-voltage distribution systems. Composed of contacts, arc extinguishing devices, operating mechanisms and tripping systems, enclosures, and control units. According to installation methods, it can be divided into two types: fixed type and drawer type. The fixed shell is made of metal material, with a larger overall size and lower protection level. The drawer type adopts an engineering plastic shell, with a relatively compact structure, high protection level, and convenient maintenance. According to the protection characteristics, ACB can be divided into non selective (Class A) and selective (Class B). Class B circuit breakers mostly use electronic overcurrent releases, which have three protection characteristics: long delay, short delay, and instantaneous action protection. The intelligent ACB is equipped with a built-in microcontroller, which has functions of displaying alarms, self checking, and communication. It can form a monitoring system with an industrial computer. The biggest feature of frame circuit breakers is their large capacity, high limit breaking capacity, and sufficient short time withstand current. For example, the Delixi CDW3 circuit breaker has a rated current of up to 6300A and a rated short time withstand current of up to 85KA, which makes ACB highly selective and stable. It is precisely because of these excellent characteristics that ACB has a higher price. MCCB is mainly used for the protection of incoming and outgoing lines and motors in low-voltage distribution systems. All parts are sealed in the casing, and auxiliary contacts, undervoltage releases, and shunt releases are mostly modular.
Due to its very compact structure, MCCBs are basically inaccessible for maintenance and are mostly operated manually. For large capacity, electric opening and closing can be selected. Due to the application of electronic overcurrent releases, MCCBs can also be divided into two types: Class A and Class B. Usually, Class A selectively protects the human body for short time delay in the event of a short circuit, resulting in no short time withstand current (lcw) value; The characteristics of molded case circuit breakers are small size, good contact protection, convenient installation and use, and low price. So what is the specific difference between molded case circuit breakers and frame circuit breakers? How to choose between the two?
What is the difference between MCCB & ACB
Firstly, in terms of appearance, the two have different sizes: ACB has a larger size and volume, while MCCB has a relatively smaller size and volume.
The intelligent release of ACB has protection functions, measurement functions, auxiliary functions, special functions, and communication functions. The protection functions include long time delay protection, short time delay protection, instantaneous protection, MCR protection, grounding protection, low voltage protection/alarm, overvoltage protection/alarm, and voltage protection/alarm
Balanced phase loss protection/alarm, phase sequence protection, low-frequency protection, instantaneous protection, MCR protection, grounding protection, low-voltage protection/alarm, overvoltage protection/alarm, voltage imbalance phase loss protection/alarm, phase sequence protection, low-frequency protection, high-frequency protection, reverse power protection, voltage harmonic alarm, current harmonic alarm · Measurement functions: current measurement, voltage measurement, power measurement, frequency measurement, electrical energy measurement, harmonic measurement; Auxiliary functions: pre alarm, self diagnosis, fault history
Recording function and testing function; Special functions: load monitoring, regional joint control, high and low temperature range; Communication function: communication protocol function, etc.
MCCB mainly has long delay protection, short delay protection (i.e. overload protection), and instantaneous protection (i.e. short circuit protection).
From this, it can be seen that the protection function of ACB is more powerful than that of MCCB.
The rated current of ACB ranges from 400A to 6300A, mainly used in distribution networks to distribute electrical energy, protect lines and power equipment from overload, undervoltage, short circuit, single-phase grounding and other faults;
The rated current of MCCB ranges from 10 to 800A, which is used to provide protection for lines and equipment in the event of overload, short circuit, or undervoltage in distribution lines. It can also provide overload, short circuit, or undervoltage protection for infrequent motor starts. The primary distribution equipment, collectively known as the power distribution center, is installed centrally in the enterprise’s substation, distributing electrical energy to subordinate distribution equipment at different locations. This level of equipment is close to the transformer side, so the electrical parameter requirements are high and the output circuit capacity is also large. Generally, in the main distribution cabinet, the main components of the secondary distribution equipment are the power distribution cabinet and motor control center. The power distribution cabinet is used in situations where the load is relatively dispersed and there are fewer circuits; The motor control center is used in situations with concentrated loads and multiple circuits. They move up one level The electrical energy of a certain circuit in the distribution equipment is distributed to the nearby load. This level of equipment should provide protection, monitoring, and control for the load, and generally choose to use circuit breakers such as molded case circuit breakers and micro disconnect switches. Different MCCBs are usually used in category A, and in the case of a short circuit, there is no short-term withstand current (lcw) value due to the selective protection of no one for short time delay;
The use category of ACB is usually Class B. In case of short circuit, selective protection has artificial short delay (adjustable), so there is a short time withstand current (lcw value) for specific use. Different circuit breaker products need to be selected according to the load situation.
How to choose MCCB and ACB?
Compared to frame circuit breakers, MCCB has lower parameters and relatively simple structure. Usually, its rated current does not exceed 1600A. As MCCBs are in the lower level of ACB, the short-circuit current will decrease after passing through a section of the line. The parameters and performance of MCCBs can meet the operational requirements, and they should be small in size, flexible in installation, and lower in price than frame circuit breakers. They are suitable for installation and use in large quantities and a wide range. Usually in use, due to the high parameters of frame circuit breakers
(The rated voltage and rated current, as well as the corresponding breaking capacity, are higher than those of molded case and micro break products.) Therefore, they are usually installed in places with high load current and fault current, requiring high safety and reliability. Frame circuit breakers are often used for incoming lines, interconnections, and feeders with high current loads. Its next level can use molded case circuit breakers. The low-voltage switches in the circuit shall be determined in the following order: low-voltage power supply – frame circuit breaker – molded case circuit breaker – miniature circuit breaker. In some special environments, products that meet the use requirements can also be selected according to the use requirements. If all parameters meet the application requirements, a molded case circuit breaker can also be used as the incoming switch for connecting the low-voltage side of the transformer.
Please contact our expert engineers to help you to select a proper circuit breaker for your power distribution system.
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