10 Questions You Should to Know about Miniature Circuit Breaker with Case

1. What is a circuit breaker?

Circuit breaker is a safety device, which ensures the safety of equipment and personnel from electric shocks and damages. They are self-acting and should safely interrupt the current flow on the event of faults. Circuit breakers are a cost-effective and efficient alternative to traditional circuit protection fuses. These devices are reusable and may help in saving a lot of money and downtime.

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2. What is a mini circuit breaker?

A miniature circuit breaker (MCB) is a protection device that prevents damage to an equipment /circuit on the event of an overload or short circuit faults. That is designed to replace MINI fuses in most applications. But the size of the circuit breaker is about twice the height of a fuse, so be sure to check that there is enough position for the circuit breakers to fit. The advantage of MCB over fuses is that MCB is reusable even after interruption of the circuit after an overload or short circuit. Moreover, MCB is more sensitive to faults than fuses. Therefore MCB is also most commonly used in the panel board at home. MCB can safely act during short circuits resulting in the current flow up to 15kA, depending on its short circuit breaking capacity. Miniature circuit breakers can be used for the protection of lighting, house electronic devices and equipment with low short-circuit currents. MCB are available in 1 Pole, 2 Poles, 3 Poles, 4 Poles and current rating from 0.5A up to 125A. Extended learning: (Type Selection and fault judgment of Miniature Circuit Breakers)

3. How do Circuit Breakers Work?

A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by excess current from an overload or short circuit. Circuit breaker is composed of contacts, arc extinguishing system, operating mechanism, tripper, mainly body. Its basic function is to interrupt current flow after a fault is detected.

When short circuit occurs, the magnetic field generated by high current over comes the reaction spring, the release pulls the operation mechanism to move, and the switch trips instantaneously. When overload occurs, electro rheological larger and calorific value increases, and bimetal sheet deforms to a certain extent to promote the action of the mechanism.

4. Can we use AC MCB for DC?

Because of the different arc-burning and arc-extinguishing processes of AC and DC, the ability of AC and DC circuit breakers with the same rated value to break DC power supply is not exactly the same. One of the main reasons for the protection of overstepping mistake operation is to use AC circuit breakers instead of DC circuit breakers. The instantaneous action of circuit breaker is based on the principle of magnetic release. Under the same fixed value, the actual rated value of AC circuit breaker in DC circuit is higher than that of DC circuit breaker.

5. What is a tandem breaker?

A tandem circuit breaker is a double circuit breaker that takes up the space of a single circuit breaker on a panel board. Because tandem circuit breakers allow for two circuits to be installed on a panel board in a one circuit breaker space, they're typically used after a panel board has been filled to capacity with standard circuit breakers.

6. How do I choose a circuit breaker?

Please follow the procedure outlined below to make sure you choose the best suited circuit protection solution for your design. First of all, make sure you list all of the required features and key parameters. What is the voltage? Is it AC or DC? If AC, what frequency? What is the normal load current? What is the trip current? Number of poles and type of poles is normally open (N/O) or normally closed (N/C)? Are any electrically separate auxiliary contacts needed? NO or NC? How many is the size constraint?

Of course, many manufacturers have selection guides to help you narrow down the choices, or consult their websites. Extended learning: (How to choose miniature circuit breaker?)

7. What is difference between MCB and MCCB?

MCB stands for Miniature Circuit Breakers, while MCCB is Molded Case Circuit Breaker. The main difference between the two is their capacity, with the MCB is mainly used for low-energy requirements, like home wiring or small electronic circuits. On the other hand, the MCCB is more suited in providing energy for high-power equipment. Generally, the MCB rated current is under 250 amps.

In this article, we discussed MCB in detail. The Full Form of MCB is miniature circuit breaker. We explained the working principle, types, and some frequently asked questions related to Miniature Circuit Breaker (MCB).

What Is An MCB?

A miniature circuit breaker (MCB) is an Electrical Switch that automatically switches off the electrical circuit during an abnormal condition of the network means an overload condition as well as a faulty condition.

Nowadays we use an MCB in a low-voltage electrical network instead of a fuse. The fuse may not sense it but the miniature circuit breaker does it in a more reliable way. MCB is much more sensitive to overcurrent than a fuse.

This is what an MCB looks like-

Handling an MCB is electrically safer than a fuse. Quick restoration of supply is possible in case of a fuse because fuses must be rewirable or replaced for restoring the supply. Restoration is easily possible by just switching it ON. Let’s look at the working of the miniature circuit breaker.

What is Inside Miniature Circuit Breaker?

A Miniature Circuit Breaker (MCB) typically consists of the following components:

1. Incoming Terminal
2. Outgoing Terminal
3. Din Rail Holder
4. Arc Chutes Holder
5. Arc Chutes
6. Fixed Contact
7. Dynamic Contact
8. Bi-metallic Strip Carrier
9. Bi-metallic Strip
10. Latch
11. Plunger
12. Solenoid
13. Switch

Main contacts: These are the contacts that carry the load current and are connected to the incoming and outgoing wires of the circuit.

Trip Unit: This is the core component of an MCB, which monitors the current flowing through the circuit and trips the breaker in case of an over-current or short-circuit. The trip unit consists of a bimetallic strip, a magnetic actuator, and an operating mechanism.

Terminal: These are the connections for the incoming and outgoing wires.

Housing: The housing is the protective casing that houses the MCB components and provides insulation between live parts and other electrical components.

Trip Indicator: An MCB typically has a visual indicator that shows whether the breaker is in the “on” or “off” position.

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Auxiliary contacts: Some MCBs have additional contacts that can be used to switch auxiliary loads or provide signalling functions.

Trip spring: This is the spring mechanism that holds the MCB contacts in the “on” position. When the trip unit operates, the trip spring releases, allowing the contacts to separate and break the circuit.

Miniature Circuit Breaker Working

Whenever continuous overcurrent flows through MCB, the bimetallic strip is heated and deflects by bending. This deflection of the bi-metallic strip releases a mechanical latch.

As this mechanical latch is attached to the operating mechanism, it causes to open the miniature circuit breaker contacts, and the MCB turns off thereby stopping the current to flow in the circuit. To restart the flow of current the MCB must be manually turned ON.

This mechanism protects from faults arising due to overcurrent or overload and short circuits.

But during short circuit conditions, the current rises suddenly, causing electromechanical displacement of the plunger associated with a tripping coil or solenoid.

The plunger strikes the trip lever causing the immediate release of the latch mechanism consequently opening the circuit breaker contacts. This was a simple explanation of a miniature circuit breaker’s working principle.

An MCB is very simple, easy to use, and is not generally repaired. It is just easier to replace. The trip unit is the main part, responsible for its proper working. There are two main types of trip mechanisms.

A bi-metal protects against overload current and an electromagnet protects against electric short-circuit current.

MCB Working Principle

If the circuit is overloaded for a long time, the bi-metallic strip becomes overheated and deformed. This deformation of the Bi-metallic strip causes displacement of the latch point.

The moving contact of the MCB is arranged by means of spring pressure, with this latch point, a little displacement of the latch causes, the release of spring and makes the moving contact move for opening the MCB.

The current coil or trip coil is placed so that during a short circuit fault the magneto-motive force (MMF) of the coil causes its plunger to hit the same latch point and make the latch to be displaced.

Again, when the operating lever of the miniature circuit breaker is operated by hand, that means when MCB goes off position manually, the same latch point is displaced as a result of moving contact separated from fixed contact in the same manner.

It may be due to the deformation of a bi-metallic strip, increased MMF of a trip coil, or maybe a manual operation, the same latch point is displaced and the same deformed spring is released, which is ultimately responsible for the movement of the moving contact.

When the moving contact is separated from fixed contact, there may be a high chance of arc.

This arc then goes up through the arc runner and enters arc splitters and is finally quenched. When we switch it on, we reset the displaced operating latch to its previous on position and the MCB is ready for another switch off or trip operation.

Miniature Circuit Breaker Types

There are several types of Miniature Circuit Breakers (MCBs) based on different factors such as the current rating, voltage rating, and trip characteristic. Some common types of MCBs are:

1. Thermal: This type of MCB trip is based on the temperature rise caused by the current flowing through the circuit. Thermal MCBs have a bimetallic strip that bends and trips the breaker when the temperature rises above a certain threshold.
2. Magnetic: This type of MCB trip is based on the magnetic force generated by the current flowing through the circuit. Magnetic MCBs have a solenoid that pulls the trip mechanism and trips the breaker when the magnetic force exceeds a certain threshold.
3. Hybrid: This type of MCB combines the features of both thermal and magnetic MCBs. Hybrid MCBs have a bimetallic strip and a solenoid, and they trip based on either the temperature rise or the magnetic force generated by the current.
4. Electronic: This type of MCB uses electronic components to monitor the current and trip the breaker. Electronic MCBs are more sensitive and provide faster and more accurate tripping compared to traditional thermal and magnetic MCBs.
5. Differential: This type of MCB is used in DC circuits and protects against earth faults and short circuits. Differential MCBs monitor the current flowing in the live and neutral wires and trip the breaker when the difference exceeds a certain threshold.
6. Residual Current Circuit Breaker (RCCB): This type of MCB is used to protect against electric shock and fire caused by earth faults. RCCBs monitor the current flowing in the live and neutral wires and trip the breaker when the difference exceeds a certain threshold.
7. Isolation: This type of MCB is used as a switch to isolate a circuit. Isolation MCBs do not have a trip mechanism and are used to switch the circuit off for maintenance or testing purposes.

Different Types of MCBs Used in Electrical Protection Systems

In the context of Miniature Circuit Breakers (MCBs), the terms Type A, Type B, Type C, Type D, Type E, and Type F refer to different levels of protection provided by the device.

1. Type A: Type A MCBs are designed to protect against over-current. They are suitable for use in circuits where the maximum expected current is known and relatively constant, such as lighting circuits.
2. Type B: Type B MCBs are designed to protect against over-current and short circuits. They are suitable for use in circuits where the load is variable, such as in motor circuits.
3. Type C: Type C MCBs are designed to protect against both over-current and earth fault currents. They are suitable for use in circuits where there is a high risk of earth fault currents, such as in circuits powered by direct current (DC) or in circuits that include sensitive electronic equipment.
4. Type D: Type D MCBs are designed to protect against over-current and earth fault currents, with a higher tripping threshold than Type C MCBs. They are suitable for use in circuits where there is a high risk of earth fault currents, but where the fault current is expected to be higher than what can be protected by Type C MCBs.
5. Type G: Type G MCBs are designed to protect against over-current and earth fault currents in residual current devices (RCDs) used in electrical systems.
6. Type H: Type H MCBs are designed to protect against over-current and earth fault currents in electrical systems that are powered by direct current (DC).
7. Type K: Type K MCBs are designed to protect over-current and short circuits in electrical systems with high fault levels.

You can check the below video to understand more about MCB.

Video Courtesy: chrvoje engineering

Contact us to discuss your requirements of mold case circuit breaker. Our experienced sales team can help you identify the options that best suit your needs.

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