Miniature Circuit Breaker (MCB)

Safety is the first concern while choosing electrical appliances or devices. When the power fluctuates or when excess current flows, it causes damage resulting in an overload or short circuit. Hence, it is important to incorporate a device as a safety element to provide overcurrent protection to the electrical devices/circuits. Fuse is one of the most common devices used in the early days for the protection of the circuit. A fuse contains a metal wire or strip that melts when overflow of current takes place, by stopping or interrupting the current.

In recent days fuse has been replaced by a much efficient and small electronic device known as MCB – Miniature Circuit Breaker.

In this article let us know more about MCB – Miniature Circuit Breaker in detail.

What Is A Miniature Circuit Breaker?

Have you ever imagined what happens to your household devices fan, washing machine, oven, fridge, and many more when a short circuit or overflow of current happens? These devices get burnt and lead to fire accidents if proper circuit breakers are not installed in the devices. Miniature Circuit Breaker is one such safety accessory that has an electro-mechanical mechanism of action.

MCB is an automatic switch that opens when excessive current flows through the circuit. MCB returns to normal automatically when the regular flow of current starts. It can be reclosed without any manual replacement. In the case of a fuse, once a fuse has been operated, it must be replaced or rewired, depending on the type of the MCB. Hence, fuse is known as one of the sacrificial devices. This is the main reason why MCBs are used as an alternative to the fuse in most of the circuits. Also, whenever there is a fault in the circuit, the switches in the MCB automatically shut down and the fault of the device can be easily detected.

Handling MCB is quite safe and it quickly restores the supply. MCB – Miniature Circuit Breaker can be reset quickly and does not demand more maintenance costs. MCB works on a bi-metal respective principle that protects against overload current and solenoid short circuit current.

The picture of MCB is as shown below.

Read More: Difference Between MCB and MCCB

Types of Miniature Circuit Breaker

MCB trip curve decides the type of MCB that has to be used for different types of appliances or devices. There are 6 types of MCBs, they are:

  • A Type
  • B Type
  • C Type
  • D Type
  • K Type
  • Z Type

A Type MCB trips off the circuit when the current exceeds 2-3 times the actual current rating. A type MCB – Miniature Circuit Breaker is highly sensitive to the short circuit and hence we can find its application in the manufacturing of semiconductors.

B Type MCB trips off the circuit when the current exceeds 3-5 times the actual current flow and finds its application in the cable protection.

C Type MCB trips off the circuit when the current exceeds 5-10 times the actual current flow and finds its application in the domestic as well as commercial appliances like transformers, fluorescent lighting circuits, IT equipment like personal computers, servers, and printers.

D Type MCB trips off the circuit when the current exceeds 10-20 times the actual current flow and offers high resistance. It finds its application in motors.

K Type MCB can withstand up to 8-12 times the actual current flow and finds its application in the heavy-duty load devices like compressors, winding motors, and X-ray machines.

Working Principle of MCB

The typical working real-time MCB is as shown in the picture below.

The component of the MCB are listed as below:

1. Latch

2. Solenoid

3. Switch

4. Plunger

5. Incoming Terminal

6. Arc Chutes Holder

7. Arc Chutes

8. Dynamic Contact

9. Fixed Contact

10. Din Rail Holder

11. Outgoing Terminal

12. Bi-metallic Strip Carrier

13. Bi-metallic Strip

When the overflow of current takes place through MCB – Miniature Circuit Breaker, the bimetallic strip gets heated and it deflects by bending. The deflection of the bi-metallic strip releases a latch. The latch causes the MCB to turn off by stopping the flow of the current in the circuit. This process helps to safeguard the appliances or devices from the hazards happening due to overload or overcurrent. To restart the flow of current, MCB must be turned ON manually.

In the case of short circuit conditions, the current rises suddenly in an unpredictable way, leading to the electromechanical displacement of the plunger associated with a solenoid. The plunger hits the trip lever, it causes the automatic release of the latch mechanism by opening the circuit breaker contacts.

An MCB is a simple, easily operable device and is maintenance-free too. MCB can be easily replaced. The trip unit is the key part of the MCB – Miniature Circuit Breaker on which the unit operates. The bi-metal present in the MCB circuit protects against overload current and the electromagnet in the circuit protects against short-circuit current.

Uses of MCB

MCB is the key component for the safety and efficient functioning of the electric machines and is used in most of the electrical appliances that are used for industrial or domestic purposes. In domestic usage appliances like lights, heaters, and fans require MCB to constantly check and protect the connection.

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Frequently Asked Questions on Miniature Circuit Breaker (MCB)

1. List the types of MCB

A type, B type, C type, D type, K type and Z type

2. Which component is more efficient: MCB or Fuse?


3. MCB works on which mechanism?

Electro-mechanical mechanism.

4. Can trip characteristics be adjusted in MCB?


5. What is the interrupting rating of MCB?

Interrupting rating of MCB is under 18000 amps.

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