Moulded Case Circuit Breakers (MCCBs) are an essential safety component of many electrical systems. MCCBs protect people, property, and equipment in the event of overcurrent or overvoltage. They are similar to circuit breakers but are more durable, have more features, and can be used in various industrial and residential setups.
Let’s take a look at the specifications and benefits of MCCBs, along with some tips for choosing the right MCCB for your unique situation.
A moulded plastic case houses the circuit breaker’s components. This offers an extra layer of protection for the breaker. The breaker has three main components—a trip unit, an operating mechanism, and an arc extinguisher.
The trip unit senses when there is an overcurrent or undercurrent. It compels the operating mechanism and arc extinguisher to work together and stop the flow of electricity. The operating mechanism opens and closes the contacts. It prevents the handle from affecting how quickly the contacts open or close. The arc extinguisher eliminates the arc, cutting off all electricity flow in the area.
MCCBs have several specifications and ratings that you can use to ensure that you get the right MCCB for your needs. Below are some of the most important.
The current rating specifics the highest current the MCCB can continuously carry while maintaining safety. MCCBs can actually carry a little over the current rating, but only for limited time. MCCBs’ current ratings range from 10A-A. Matching the current rating with your machinery’s current should be your first consideration when choosing an MCCB
The breaking capacity is the highest voltage an MCCB can interrupt without damaging equipment or the arc. Choose an MCCB with a high enough breaking capacity to manage your equipment.
MCCBs allow you to adjust tripping characteristics to meet your needs. You can set the MCCB to trip at various overload currents.
Article that you may be interested in: The Basics of Molded Case Circuit Breaker (MCCB)
 
One of the MCCB’s most significant benefits is its durability. Since it’s enclosed, it is less susceptible to the elements and prevents dust from getting into the circuit breaker. MCCBs last longer and are more dependable.
MCCBs are more compact than traditional circuit breakers. This makes it easier to integrate them into almost any system. This is particularly important in settings where space is limited.
MCCBs can withstand higher currents. This makes it a better option for heavy-duty equipment such as welding equipment, large motors, and others.
MCCBs also have customizable trip settings. It allows the circuit breaker to be adjusted to handle the specific current characteristics of different applications, such as the inrush of current in motor starting. This protects the motor from overload.
Many MCCBs have built-in protection features, such as thermal-magnetic or electronic trip units. This provides additional protection in case of overloads or short circuits.
Lastly, MCCBs are versatile. It can be used for various applications, from commercial buildings to industrial applications.
Durable
Work in a variety of setups
Can be configured to manage different issues
Easy to reset
Easier to maintain and less costly in the long run
Choosing the right Molded Case Circuit Breaker is crucial for the safety of your workers and equipment and for ensuring optimum system efficiency. Here are some key factors to consider when selecting an MCCB:
Remember to consider the operating current and fault currents when sizing an MCCB. Ensure the working voltage is similar to the system’s voltage. Also, check if the trip range allows appropriate adjustment to the load current. Lastly, the breaking capacity should be higher than all possible fault currents.
Moulded Case Circuit Breakers serve a variety of situations and have many benefits. While they may cost more than a conventional circuit breaker, features like customizable trip lines, easy resets, and durability make them a worthwhile investment.
Chint Global is a leading manufacturer of electrical products, including the NM5C-100 MCCB. It is a compact-size Moulded Circuit Breaker with a high breaking capacity and up to V of High DV voltage. It’s also designed for easy installation.
Contact Chint today to learn more about the NM5C-100 MCCB and other products. We’re here to help you keep your systems safe and reliable.
How does an MCCB differ from an MCB?
Can the trip settings of an MCCB be adjusted?
Can MCCBs provide ground fault protection?
A circuit breaker is an electrical switch that protects the circuit or load against faulty currents. This circuit breaker utilizes air as the dielectric medium to break an electrical circuit. Here, air has lower dielectric strength compared to other mediums, and is thus utilized for protection within low voltage circuits. An MCCB can use different mediums to extinguish the arc, such as air, SF6, oil, or vacuum. So they detect faults with protective relays. Whenever a fault is noticed, the circuit breaker trips & shuts off the current. Unlike fuses that must be replaced, CBs can be reset manually or automatically. These electrical devices are used in offices, homes, industrial areas, etc. This article provides an overview of a Molded Case Circuit Breaker (MCCB), their working principle and applications.
The MCCB or Molded Case Circuit Breaker is a significant component within electrical systems that provides short-circuit protection and overload protection to a circuit. Generally, these are installed within the major power distribution boards, which allow the system to be simply shut down whenever required. These are available in different sizes and ratings based on the electrical system size. These circuit breakers stop the current automatically whenever the current goes beyond the trip setting. These circuit breakers usually include thermal magnetic trip units, whereas large molded case CBs are equipped with solid-state trip sensors.
MCCBs are generally operated electrically or manually and with large capacity. These can be classified into different types based on electronic over-current tripper applications, such as Class A and Class B. So Class B type CBs have good three-stage safety characteristics but due to the cost the market share of Class A products is higher due to their use of thermal-magnetic trippers..
A Molded case circuit breaker includes contacts, arc extinguishing chambers, trippers, and operating mechanisms in a plastic case. Generally, maintenance is not considered. It is suitable for protective switches used as a bypass. Overcurrent trippers are of a thermal-magnetic type and electronic type.
The construction of a molded case circuit breaker can be done with different components which include an Arc chute, Contacts, operating mechanism, terminal connector, thermal trip unit, magnetic trip unit, handle / trip-free mechanism, and trip button. So the molded case circuit breaker diagram is shown below.
Arc chute includes a set of parallel metal plates made with ferromagnetic material. These are insulated mutually from each other. So this circuit breaker helps in quenching the arc by dividing the arc & lengthening it which is called an arc splitter or arc divider.
Metallic conductors, like contacts are responsible for carrying the current supply to the electric load. So these are available in two types fixed & moving contact which are made from arc resistance material which have corrosion & low resistivity. The circuit breaker’s lifetime is decided by the material’s quality.
The MCCB’s mechanism is responsible for opening & closing the current-carrying contacts. So it is simply connected through a trip unit that activates the operating mechanism. Here the trip unit works on a magnetic & thermal mechanism.
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This connector helps in connecting the circuit breaker to the outside circuit. So the higher terminals are connected to the load whereas the bottom terminals are to the supply. Even though they are bi-directional, the designation of input & output is because of their physical installation.
The MCCB’s trip unit activates the operating mechanism. So it comprises a thermal mechanism mainly for overload and magnetic tripping for a test button and short circuits for testing.
It utilizes a thermal mechanism like a bimetallic strip that opens the contacts whenever the temperature increases because of the overloading.
This trip unit includes a relay that produces a magnetic field when high current flows through the solenoid due to a short circuit, it trips the CB. When the test button is utilized to replicate the above mechanisms & test the circuit breaker response.
It is used to control the circuit breaker manually by opening or closing. The handle can also be called a trip-free mechanism as it trips even if the handle is in the ON position. Generally, the handle of this CB could be in any three positions upward, downward, or middle. If it is in an upward place it will be in place. Similarly, if it is in the middle position, it indicates the breaker has tripped, while the downward position indicates OFF.
It is a red-colored button, used to test the circuit breaker. When it is pushed then it trips the operating mechanism.
A molded case circuit breaker works by protecting a circuit against fault current. It uses both magnetic and thermal mechanisms. The magnetic mechanism is used to protect short circuits, whereas the thermal mechanism is to protect overload.
Overload happens whenever the current surpasses a limit for an extended period. This circuit breaker includes a thermal mechanism that includes a bimetallic contact to defend from overload. A bimetallic strip is designed with two different kinds of metal with different thermal expansion rates. The main current flows through the bimetallic strip, which bends or contracts on temperature change.
If the current supply exceeds a certain limit, then bimetallic contact heats up & expands. The strip bends and trips the circuit because of the different expansion rates.
The current in electrical devices can overload for short time durations; it is normal & should not be measured as fault current. So, this circuit breaker has a time delay that permits the overload current for a short time duration before circuit tripping.
MCCB protects from a short circuit with a solenoid that generates electromagnetic force. So the main current supplies throughout the solenoid that attracts & repels a plunger accountable for circuit breaker tripping. If the current remains in the threshold, then the solenoid produces a weak magnetic force that cannot attract the plunger. During a short circuit, very high current supplies throughout the solenoid generate a very strong magnetic force. So it attracts the plunger that trips the circuit.
The MCCB specifications include the following.
Here the proper MCCB wiring diagram is shown below. MCCB is a protective device that protects the electrical equipment or electrical circuit from two main electrical faults like short circuits and over currents. As compared to MCB, this circuit breaker is designed to provide almost high to very high currents. MCCBs are used mostly for industrial-based high-current applications like motor circuits, used as incoming breakers within LT panels, elevators, CNC machines, electric cranes, and many more.
The wiring connections of this circuit breaker follow as;
If you observe the above wiring diagram, this circuit breaker includes a total of six terminals where three are input terminals & remaining are output terminals. Usually, most of the circuit breakers are designed to connect the input supply at the base and the output at the top.
Thus, you can observe that all three R, Y, and B phases of the input power supply are connected to the base side of the circuit breaker, while the outgoing terminals are connected to the upper side. These outgoing terminals are then connected to a busbar, which distributes power to multiple loads connected to the same circuit. The busbar helps simplify wiring and ensures balanced load distribution across connected devices.
Molded case circuit breaker types are explained below.
Type B MCCBs are designed to trip whenever the current flowing through them exceeds 3 to 5 times their rated current. The tripping time for this circuit breaker ranges from 0.04 to 13 seconds. Generally, these types of MCCBs are installed in industrial and commercial building distribution boards with lower fault currents. Therefore, they are frequently used with resistive loads like heating and lighting.
These MCCBs provide more protection compared to Type B MCCBs. They trip at 5 to 10 times the rated current with a delay time of 0.04 to 5 seconds. Type C MCCBs offer a balance between short-circuit and overload protection. They are suitable for industrial and commercial applications involving equipment with moderate inrush currents, such as transformers and motors.
Type D MCCBs are designed for high-inrush current applications such as large industrial machinery. These breakers trip at 10 to 20 times the rated current, and their response time ranges from 0.04 to 3 seconds. They are used in environments where substantial equipment frequently starts and stops. Their high tolerance to inrush currents makes them ideal for heavy-duty operations, such as those involving compressors, lifts, engines, etc.
Type K MCCBs are mainly effective in protecting circuits that use two-core cables. They trip at 8 to 12 times the rated current and are commonly used in installations with sensitive equipment. These MCCBs provide excellent feeder protection and can operate for up to 5 seconds, making them ideal in environments where surge currents are common.
Type Z MCCBs trip at just 2 to 3 times the rated current. They are used to protect sensitive electronic equipment in applications such as data centers and telecommunications. Although less versatile than other MCCB types, they respond to small overloads and are essential in sensitive circuits. These highly sensitive MCCBs can tolerate only 1.5 to 3 times the rated current and are best suited for electronic loads requiring high-speed tripping.
The difference between the molded case circuit breaker and the air circuit breaker is shown below.
MCCBACB
The term MCCB stands for molded case circuit breaker. ACB stands for air circuit breaker. These are compact and fit in small distribution panels. These circuit breakers are larger because of their high current ratings, They have magnetic, electronic, and thermal-magnetic trip units. They have electronic or thermal-magnetic trip units. MCCBs have low current ratings up to Amps. ACBs have high current ratings up to amps. It uses a combination of different technologies to quench the arc, frequently depending on a plastic housing mainly for insulation. It uses air to quench the arc by operating at atmospheric force. These are normally not designed for simple repair & may need whole unit replacement. ACBs are frequently designed to be stronger and may be simple to repair. These are generally not as expensive as compared to ACBs. These are more expensive.The characteristics of MCCB include the following.
The advantages of MCCB include the following.
The disadvantages of MCCB include the following.
The applications of MCCB include the following.
Where are molded case circuit breakers used?
MCBs are used in large commercial and industrial settings for high-current circuits, so they protect short circuits, equipment failures, overloads, etc.
Does a molded case switch trip?
Yes, an MCCB does trip to defend against short circuits & overloads.
How does a molded case breaker protect against sustained overloads and short circuits?
MCCBs defend from short circuits and sustained overloads with a blend of magnetic trip and thermal mechanisms. Magnetic protection reacts to immediate high currents and thermal protection notices prolonged over currents.
What two elements make up a molded-case circuit breaker?
A thermal element is used for overload protection, whereas a magnetic element is used for short-circuit protection.