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What is a Molded Case Circuit Breaker

Author: Site Editor     Publish Time: 2023-08-09      Origin: Site

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What is a Molded Case Circuit Breaker

What is a Molded Case Circuit Breaker (MCCB)?

MCCB, known as Molded Case Circuit Breakers, are also known as device circuit breakers, which are used to protect circuits from dangers caused by current overloads and short circuits.

MCCB offer greater reliability, adjustability and reusability than traditional fuses.

Its case is usually made of high-strength plastic to isolate the conductors from each other and from the grounded metal part, while the interior contains sophisticated electronic components such as electromagnetic triggers, interrupting chambers, strippers and operating mechanisms, etc. Due to its very compact structure, the molded case circuit breaker is basically inaccessible.

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Working principle of MCCB:

The main contacts of the low voltage circuit breaker are operated manually or closed electrically. After the main contact is closed, the free release mechanism locks the main contact in the closed position. The coil of the overcurrent striker and the thermal element of the thermal striker are connected in series with the main circuit, and the coil of the undervoltage striker is connected in parallel with the power supply.

When the circuit is short-circuited or severely overloaded, the armature of the overcurrent striker suctions, causing the free release mechanism to operate and the main contact to disconnect the main circuit.

When the circuit is overloaded, the thermal element of the thermal striker heats up to bend on the bimetal, which pushes the free stripping mechanism into action, and the main contact disconnects the main circuit.

When the circuit is undervoltage, the armature of the undervoltage detent is released, which also makes the free detent mechanism act, and the main contact disconnects the main circuit.

When the shunt release button is pressed, the armature of the shunt release device is attracted, which causes the free release mechanism to operate and the main contact to disconnect the main circuit.


Application areas of MCCB:

MCCB are widely used in a variety of electrical systems, including industrial, commercial and residential applications. In the industrial sector, MCCB protect critical production equipment and machinery against production interruptions caused by overloads and short circuits. In commercial buildings, MCCB are used for power distribution and equipment protection to ensure the safe operation of the building. In homes, MCCB can ensure the safety and stability of home electricity.


YUMONN mainly produces AC Molded Case Circuit Breakers and DC Molded Case Circuit Breakers.


What is the difference between AC Molded Case Circuit Breaker and DC Molded Case Circuit Breaker?


Although DC Circuit Breakers and AC Circuit Breakers are both important devices used to protect circuits in an electrical system, they are not common to each other. The main reason for this is:


The current in a DC circuit is unidirectional, while the direction of the current in an AC circuit is constantly changing.

DC circuits are prone to arc, and arc fusing capacity, while the arc in the AC circuit with the change in the direction of the current will automatically disconnect, so you need to choose a special design of the AC circuit breaker to cope with the arc.

DC circuits in the relatively low voltage level, AC circuits in the higher voltage level, both use the circuit breaker also needs to be designed according to its specific power requirements.


In addition to the above differences in electrical characteristics and design requirements, on the other hand there are the following differences between DC and AC circuit breakers:


DC circuit breakers have relatively slow opening and closing speeds, whereas AC circuit breakers require fast response.

DC circuits have virtually no inductive loads, whereas AC circuits often have inductive loads, so AC circuit breakers need to consider how to limit overvoltage caused by inductive loads.

DC systems usually use fuses to protect the circuit, while AC systems use not only circuit breakers but also other devices such as fuses and disconnect switches.

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Characteristics of DC Circuit Breakers

DC circuit breakers have the following characteristics:


The rated voltage is relatively low, usually below 1000V;

Large fusing capacity, usually up to a thousand amperes or more;

In general, not automatically tripped, need to manually cut off the current;

Easily generate a large number of arcs when disconnecting current, requiring the design of special arc extinguishing measures;

Strong short-circuit withstand capacity, can withstand instantaneous high current impact.

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Features of AC circuit breaker

AC circuit breaker has the following characteristics:


The rated voltage is relatively high, usually above 1000V;

The fusing capacity is relatively small, usually below several hundred amps;

Can be automatically tripped, automatic protection function is relatively complete;

Need to consider the overvoltage generated by inductive loads;

Arc extinguishing capacity is weak, requiring the design of special arc extinguishing measures.

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