In the electrical industry, a moulded case circuit breaker (MCCB) is referred to as the full form of MCCB. It is an automatic electrical device that protects electrical equipment against overload, short circuit, instantaneous over current, and earth fault. It is also known as a circuit breaker. It is a more advanced variant of the MCB system (Miniature circuit breaker). It is available in a variety of currents ranging from 32 amps to 1600 amps and voltages ranging from 230V to 1.1kV.

The key advantage of MCCB (moulded case circuit breaker) is that we can customize it to meet our specific needs by installing it with additional features such as remote closure, ultraviolet trip, and so forth. It is the most cost-effective replacement for an air circuit breaker, and it also performs better in terms of functionality. In addition, you can alter the current setting as well as the time setting in the circuit breaker with a moulded housing.

Diagram with a single line:


Arc chute

It is a stack of parallel metal plates that separate the arc in the moulded case circuit breaker. Steel and glass fiber are used to construct arc chutes.

Contact shifting

Rather than using metal as a moving contact, electrolyzed brass is employed. The moving contact’s MOC (Material of Construction) should have good arc resistance, corrosion resistance, and low resistivity, among other characteristics. The MOC is in charge of determining the life lifetime of the MCCB.

Mechanics of operation

It is concerned with the process of opening and closing contacts. There is no relationship between the speed of the operating mechanism and how quickly it is moved. An example of this is a quick make and quick break.

It will be linked to the relay’s functioning mechanism in some manner.

Aside from that, breakers are constructed with a test mechanism that allows the breaker to be manually triggered.

Cover for the Base

It is primarily utilized as a base cover for the Moulded case circuit breaker and is made out of a closed assembly of glass-fiber reinforced thermoset polymer material. It improves the mechanical strength of the material. Almost all of the components of the MCCB will be housed within these enclosures.

Connector for the terminals

The terminal connector is a bolt arrangement composed of steel material that connects two pieces of wire together. Its purpose is to connect the external circuit to the MCCB and vice versa. For the most part, a terminal connector is comprised of an Allen’s head (hexagonal) with 8.8 Ton torque range bolts. In this way, it makes certain that there is no slack contact between the terminals.

If the rating of the MCCB is greater than 400Amps, the terminal connector will be provided with a spreader link assembly, which is a type of connector assembly.

They are used to connect MCCB to higher current rating cables because the cable size for higher current ratings will be larger than for lower current ratings.

More Information: How Does a Centrifugal Switch Work?

Contact with a Bimetallic Component

In order to create a bimetallic contact, a temperature-sensitive component composed of steel and copper material is used. It is necessary to connect a bimetallic contact in series with the line current.

As a result, the bimetallic contact will always be used to conduct the entire line current of the circuit breaker.

It is utilized to trigger the circuit breaker in the event of an overload situation.

Knob with a handle

It is used to manually close or open a contact when necessary. Furthermore, you cannot force the breaker to cease tripping by holding the knob on the top side of the breaker. It’s referred to as a “free trip.”

The status of the breaker is indicated by the handle knob, which indicates whether it is in the ON or OFF position.

When the handle is in the up position, it is referred to as the ON position, and when it is in the down position, it is referred to as the off position. If it is tripped, the handle will be in the center of the handlebar position.

Trip button that can be operated manually

A manual trip button is a red-colored button that is related with the functioning mechanism of the device. It is mostly employed for the purpose of manually tripping the breaker for testing purposes.

Working Philosophy: The MCCB’s operating principle is straightforward…. To illustrate this, consider the following three types of fault conditions: overload, short circuit, and earth fault.
Trip due to overload
When a current flow exceeds the rated current for a predetermined period of time, this is referred to as overloading the system. Actually, it isn’t a defect; rather, it is a state of affairs.

The bimetallic contact is involved in the overload operation of the circuit breaker; under normal conditions, it permits current to flow through the circuit breaker. If the current flow exceeds the predefined value, the current will be bent, and the tripping mechanism will be activated as a result of the bend. The trip mechanism is responsible for opening the breaker. Consider the image that is provided below.

Furthermore, a bimetallic contact will prevent the breaker from being reset instantaneously. Because it takes some time for it to return to its original state.

Depending on your load demand, the setting for Over Load will be between 80 and 100 percent of the full load current and the dame. However, there will be a temporal delay of 10 to 15 seconds.

Instantaneous/earth fault trip:

The electromagnetic coil protects the breaker from short circuits and ground faults. In normal settings, the CT generates less current, thus the coil’s electromagnetic field cannot draw the plunger. So the breaker stays off.

In a short circuit, the CT generates high current and the coil generates a strong magnetic field. So the coil pulls the plunger, tripping the circuit.

A short circuit is often set at 2.5 times the overload setting, with a time delay of 0.2 to 0.5 sec.

A typical immediate fault setting is 4 times the overload value, with no time wait.

Trip to the Earth Fault Leakage:

Earth leakage protection differs significantly from other types of protection. It is a custom-made suit. The addition of CT is required, which must be fitted in the circuit breaker casing that is moulded into the wall.

The current transformer’s output will be connected in a star configuration. Normally, the current flow through the star’s neural point will be 0 because the star is not moving. If a leakage is discovered in the line means, the identical leakage will be detected at the star terminal. If the leakage flow exceeds the permitted limit, the MCCB will trip the circuit and shut down the system.

Reduce the amount of space taken up by the electrical panel.

Adjustable current settings are less expensive than ACBs.


The fault clearing times are significantly faster than those of the fuse units.

There will be no need to retain spares, which will result in a reduction in inventory.

Applications in the industrial and commercial sectors are suitable.

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