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What is the difference between MCCB and ACB?

From: Quisure2020-10-23

What is the difference between MCCB and ACB?


Moulded case circuit breaker and air circuit breaker are very common products, but many people do not understand the difference between them, so it is easy to confuse them in practical application. Air circuit breaker has large capacity, high limit breaking capacity, good short-time withstand ability and good stability, but it is expensive. It is mostly used for main switch of low-voltage distribution system, trunk line with large load and protection of large motor. Compared with air circuit breaker, moulded case circuit breaker has the advantages of small volume, good contact protection, convenient installation and low price, but it has small capacity and poor short-time tolerance, so it is suitable for branch protection switch.


Molded case circuit breaker

Molded case circuit breakers(MCCBs) automatically cut off current when the current exceeds the trip setting. Plastic housing refers to the housing of a device using a plastic insulator to isolate between conductors and the grounded metal part. Molded case circuit breakers usually contain thermal magnetic trip units, while large moulded case circuit breakers are equipped with solid state trip sensors. Due to the very compact structure, the moulded case circuit breaker can hardly be serviced.


What is the difference between MCCB and ACB?

Nader Molded case circuit breaker (NDM2-250 Series)


Air circuit breaker

Air circuit breaker(ACB) is a mechanical switching device which can turn on, carry and break current under normal circuit conditions, and also turn on and carry certain time and break current under specified abnormal circuit conditions. Air circuit breakers are used to distribute electric energy and protect lines and power supply equipment from overloads, undervoltages, short circuits, etc.


What is the difference between MCCB and ACB?

Nader Air circuit breaker (NDW1-1600 Series)


Air circuit breakers generally have a steel frame, and all parts are installed in the frame. It has a large capacity, can be installed with multiple functions of tripping devices and more auxiliary contacts, has a higher segmentation capacity and thermal stability, so it is often used in places that require high breaking capacity and selective protection.


Difference between moulded case circuit breaker and air circuit breaker

The appearance and installation size are different

From the appearance, the size of moulded case circuit breaker is different from that of and air circuit breaker. The size and volume of ACB are larger, while that of MCCB is relatively small. Moreover, the current level and breaking capacity of air circuit breaker are greater than those of molded case circuit breaker.


The protection function of the release is different

The intelligent release of air circuit breaker has protection function, measurement function, auxiliary function, special function and communication function.

Protection functions: long time delay protection, short time delay protection, instantaneous protection, MCR protection, grounding protection, low voltage protection/alarm, over-voltage protection/alarm, voltage unbalance phase loss protection/alarm, phase sequence protection, low-frequency protection, high-frequency protection, reverse power protection, voltage harmonic alarm and current harmonic alarm.

Measurement function: current measurement, voltage measurement, power measurement, frequency measurement, electric energy measurement, harmonic measurement.

Auxiliary functions: pre alarm, self diagnosis function, fault history record function and test function.

Special functions: load monitoring, regional joint control, high and low temperature range.

Communication function: communication protocol function.


The release of moulded case circuit breaker mainly has the functions of long time delay protection, short time delay protection (i.e. overload protection) and instantaneous protection (i.e. short circuit protection).


It can be seen from here that the protection function of air circuit breaker is more powerful than that of moulded case circuit breaker.


The scope of application is different

The rated current range of air circuit breaker is usually 400-6300A, which is mainly used in distribution network to distribute electric energy, protect lines and power equipment from overload, undervoltage, short circuit, single-phase grounding and other faults.


The rated current range of moulded case circuit breaker is usually 10-800A, which is used to provide protection for lines and equipment in case of overload, short circuit and under voltage of lines and equipment in distribution lines. It can also provide overload, short circuit, and undervoltage protection for scenes where the motor is not frequently started.


The primary distribution equipment, collectively referred to as the power distribution center, is installed in the substation of the enterprise to distribute electric energy to the lower level distribution equipment in different locations. This level of equipment is close to the step-down transformer, so the requirements for electrical parameters are high, and the output circuit capacity is also large. Generally, in the main distribution cabinet, the main component is the air circuit breaker.


Secondary power distribution equipment is the general name of power distribution cabinet and motor control center. The power distribution cabinet is used in the situation where the load is dispersed and the circuit is less; the motor control center is used for the occasion where the load is concentrated and the circuit is more. They distribute the electrical energy of a circuit of the upper power distribution equipment to the nearest load. This class of equipment should provide protection, monitoring and control of the load. The circuit breakers commonly used are moulded case circuit breaker, micro break switch and dual power supply products.


Different types of use

Moulded case circuit breakers are usually class A. in the case of short-circuit, the selective protection is not short-time delay, so there is no short-time withstand current (ICW) value.

The air circuit breaker is usually classified as class B. In case of short circuit, the selective protection has artificial short time delay (adjustable), so it has short-time withstand current (ICW) value.


Index contentAir circuit breakerMoulded case circuit breaker
Rated voltageHigher(Up to 1140V)Lower(Below 660V)
Rated currentGenerally 200 ~ 6300AMost of them are below 600A
SelectivityWith short time delay, it can meet the requirements of selective protectionMost of them have no short time delay and can not meet the requirements of selective protection
Short circuit breaking capacityHigherLower
Release settingVarious release devices can be installed to meet different protection requirementsMost of them only have over-current, voltage loss and shunt excitation, and only one of them can be selected
Scope of applicationSuitable for main switchSuitable for branch switch
Operation modeThere are many changes, such as handle, lever electromagnet and motor operationLess change, mostly handle, also with motor drive mechanism
Contact protectionPoorGood
MaintenanceMore convenientInconvenient, most of them don't consider maintenance
Installation modeSuitable for installation in switch cabinet. There are products with drawer structureIt can be installed separately or in the switch cabinet
Isolation performanceBetterWorse
Short time withstand currentLargerSmaller
Arcing distanceLargerSmaller
DimensionsLargerSmaller
PriceHigherLower

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