Miniature Circuit Breaker (MCB) : Circuit, Working, Types, Differences & Its Applications

Safety is the main concern while using electrical devices or appliances because whenever excess current flows or power fluctuates then it causes harm to the appliances and it can cause short circuits or overload. Therefore, it is necessary to integrate a device like a fuse or MCB to give protection to the electrical circuits or devices from overcurrent. Earlier, the fuse is the most frequently used safety device used for protecting the circuit. But at present, the fuse is replaced by a miniature circuit breaker or MCB because it is a small, very efficient device and also provides better security & control. There are a wide range of MCBs available in the market with 10KA – 16 KA breaking capacity, used in commercial, industrial & domestic applications. This article provides brief information on miniature circuit breaker or MCBs.

What is Miniature Circuit Breaker(MCB) ?

A miniature circuit breaker (MCB) is an electromagnetic device used to open the circuit automatically once the current flowing throughout it exceeds the set value. This MCB can also be switched ON & OFF like a normal switch if required. These devices are rated at 220Volts for DC supply whereas, for AC supply, it is rated at 240/415 including different short circuit current abilities. MCBs perform various functions like local control switches, overload protection devices for specific appliances or equipment & isolating switches against errors. The miniature circuit breaker diagram is shown below.

The working principle of MCB is to detect the flow of current throughout electrical circuits. If the flow of current goes beyond the highest set range, then it will trip & interrupt the electrical circuit automatically.

Miniature Circuit Breaker Circuit Diagram

The connection diagram of a single pole miniature circuit breaker with a common neutral for loads is shown below. In this circuit, MCB is used to protect the electrical equipment or circuit from two main hazardous electrical faults like. Short circuit fault & overload fault. These MCBs are generally available in various current ratings like 6A, 32A, 16A, 10A, etc. Single pole miniature circuit breakers are used wherever all individual loads neutral are connected mutually & the MCB is connected through the phase wire.

The required components to make this connection diagram mainly include MCBs with 16A, 6A, 16A & 32A, and loads. The connection of this circuit follows as;

First, need to choose a miniature circuit breaker with a correct rating that should be suitable for your load.

Make sure the MCB’s input & output side may be printed or written on your circuit breaker. If the input and output are not mentioned on the MCB, it is fine to connect the input downside & output upside.

If you have various loads & they are connected through common neutral then build the circuit as shown above.

Working

In the above diagram, we can notice that all the individual loads are connected to a common neutral however each has a separate single pole MCB. Once any short circuit fault/overload occurs by a load, then the circuit breaker for that load simply tripped & the remaining loads will normally function. You can also observe, some of the loads are connected by a similar rating & some of the loads are connected through a different rating based on the requirements.

Types of MCCB

MCCBs are classified into different types which are discussed below.

Type B Circuit Breaker

Type B circuit breaker is the most sensitive type which is mainly designed to trip whenever the flow of current is 3 to 5 times the rated current by 0.04 to 13 Seconds of an operating time. The main functions of this circuit breaker are to protect & control different circuits against short circuits & overloads; the protection of people as well as big-length cables within IT & TN systems.

This type of MCB is used in domestic applications as well as low-voltage commercial settings wherever any current surges are very small. Type B CBs are mostly used in light commercial or residential applications wherever the loads connected are mostly lighting fixtures or domestic devices by mostly resistive elements. These circuit breakers are also used in electronic equipment & computers with extremely low inrush loads. So in such cases, the levels of surge current are quite low.

Type C MCB

Type C MCB trips between 5 to 10 times full load current as compared to the rated current with 0.04 to 5 Seconds operating time. The main function of this MCB is to protect & control the circuits against short-circuits & overloads and also protect against inductive & resistive loads by low inrush current.

The loads connected to this MCB are mainly fluorescent lighting or induction motors which are inductive within nature. This MCB is used in industrial or commercial type of applications wherever there is a chance of high short-circuit currents occurring within the circuit.

Type D MCB

Type D MCB mainly trips between 10 to 20 times full load current with 0.04 to 3 Secs an operating time. The main function of Type D MCB is to protect & control the circuits from short-circuits & overloads. It protects different circuits which supply high inrush current loads at the closing circuit. These types of MCBs are mainly utilized in commercial or specialty industrial applications wherever inrush current can be highly changed. The Type D MCB examples are X-ray machines, large winding motors, transformers, and many more.

Type K MCB

Type K MCB is used to trip between 8 to 12 times full load current with below 0.1 Seconds operating time. The main function of Type K MCB is to protect & control the circuits from short-circuits & overloads like transformers, auxiliary circuits & motors. Type K MCBs are Suitable for inductive and motor loads with high inrush currents.

Type Z MCB

Type Z MCB trips between two to three times full load current. The main function of this MCB is to protect as well as control electronic circuits from short circuits, long duration, and weak overloads These MCBs are extremely responsive to short circuits & are applicable for protecting highly sensitive semiconductor devices. These MCBs are used in industrial and commercial applications.

MCB Types based on the Number of Poles

MCBs are classified into different types based on a number of supported poles like a single pole, double pole, triple pole, and four poles MCB which are discussed below.

Single Pole MCB

A single-pole miniature circuit breaker is used to provide switching as well as protection for only one phase of a circuit. These circuit breakers are mainly designed to use in low-voltage circuits. These circuit breakers help in controlling particular electric lines, lighting systems, or socket outlets within your home. These can also be used for vacuums, general lighting outlets, outdoor lighting, fans, air compressors & hair dryers.

Double Pole MCB

A Double pole MCB is normally used in consumer control unit panels like the main switches. From the energy meter, the power supplies throughout this circuit breaker before it is scattered to different divisions of the house. This MCB is used to provide protection & switching for both a phase & the neutral.

Triple Pole MCB

A triple pole MCB or TP MCB is used to provide only switching as well as protection to the circuit’s 3-phases & not to the neutral.

Four Pole MCB

A four-pole MCB looks like TPN but additionally, it has a protecting release mainly for the neutral pole like in the phase poles. So, this type of MCB must be utilized wherever there is a chance of a high neutral flow of current throughout the circuit.

Miniature Circuit Breaker Vs Molded Case Circuit Breaker

The difference between a miniature circuit breaker vs molded case circuit breaker includes the following.

Miniature Circuit Breaker Vs. Fuse

The difference between a miniature circuit breaker and a fuse is discussed below.

 How to Select the Correct MCB?

The selection of MCB mainly depends on different factors which are discussed below.

• Before selecting, you have to make sure that the capacity of short-circuit breaking is equivalent to or above the line capacity.
• The MCB setting current should be below 80% at the terminus of the short-circuit current.
• The breaking capacity is the highest current that a circuit breaker interrupts without releasing or destroying an arc. These are simply measured in kA.
• The no. of trippable switches/poles within the housing of MCB.
• The rated current value of the CB can resist without tripping. So, miniature circuit breakers have 0.5A to 125A rated current. Initially, you should decide on the whole circuit current after that, you must choose the suitable MCB.
• Tripping characteristics simply define the relationship between current versus tripping time. So these are distinguished on the immediate range of tripping. You must decide on the tripping class depending on the loads to be sheltered.
• Based on the number of poles to supply the required protection.
• Operating and insulation voltage.

Advantages and Disadvantages

The advantages of a miniature circuit breaker or MCB include the following.

• A miniature circuit breaker is more responsive to current as compared to a fuse.
• It detects the defects that occurred within the flow of current & turns off the circuit automatically.
• It provides a better interface using a knob.
• MCB handling is safer electrically.
• It is reusable.
• It needs less maintenance.
• It quickly responds against short circuits as well as overload because of its sensitivity.
• It is more reliable.
• Its replacement cost is less.
• It is very easy to use.
• It turns off the electricity & supply connections automatically.
• It recognizes faulty circuits.
• It has good performance.
• MCB gives good performance in earth leakage as well as faulty circuit identification.
• This circuit breaker has a time delay characteristic so it works more correctly.

The disadvantages of miniature circuit breakers or MCBs include the following.

• MCB is expensive as compared to fuse & MCCB.
• MCB includes a metallic strip, so aging problems will occured over time.
• It cannot work & protect properly against the faults of the earth.
• It is applicable only for small current-carrying-based applications.
• Auxiliary contact within the MCB circuit does not occur.
• The cost of the distribution board is high compared to the rewireable board of the fuse.
• It cannot function properly & defend against the faults of the earth.
• It is used only for small current-carrying-based applications like the protection of home wiring.
• In MCB, auxiliary contact does not happen.
• Current protection is limited from other kinds of electrical hazards like lightning strikes/ voltage surges.
• Over-current rating is limited so they protect circuits only up to certain amperage.
• These are sensitive devices so they can trip because of small changes within the flow of current.
• MCBs need to be changed once they trip because they cannot be reset.
• It provides limited protection for high-power-based appliances.

Applications

The applications of miniature circuit breakers or MCBs include the following.

• The main function of an MCB is to protect an appliance or device from short-circuit and overload conditions.
• It is installed in homes, shops, offices, etc.
• It protects the home against the overload of the circuit.
• MCBs replace the usual rewireable fuses.
• It can be utilized by an arc-fault or GND fault mechanism as it includes a system that simply opens the contacts once a fault from line to GND occurs.
• It is more expensive than fuses.
• It can be used with arc fault or GND fault mechanism.
• MCBs are used as effective protection devices in small scale & large-scale industries
• MCBs play a significant role in effective electricity distribution across all house lighting systems.
• It protects the home from overload.

Thus, this is an overview of miniature circuit breakers, their working, types, circuits, advantages, disadvantages, and applications. MCB is an electromechanical device mainly designed to switch off the electrical circuit automatically once it detects any deviation. This circuit breaker senses easily the over current caused by the short circuit. Here is a question for you, what is a circuit breaker?