Miniature Circuit Breakers – Working Principle and Different Types

Posted by Tarun Agrawal
October 28, 2017


MCB, which is an abbreviated form of miniature circuit breaker, is an electrical device that protects electric circuit from over current. This over current passes through circuit by result of short circuit, faulty design or overload. MCB is far better alternative to fuse as it doesn’t need any replacement when the overload is detected by it. Unlike the fuse, miniature circuit breaker can be operated effortlessly and in this way, provides improved safety while in use and convenience without asking for big operating amount. The electrical product is utilized to protect the circuits with low current and are normally in range between 0.5 A to 100 A. Its rating of short circuit is given in KA (kiloamps), which tells us its work ability.

The Working Principle

Miniature circuit breaker is a protective device that is produced to break circuit when an incident of short circuit or overload takes place. To protect from overload related issue, the electrical item has Bi-metallic strip causing circuit to open. And when short circuit happens it is electromagnetic type of thing.

There are two types of operation arrangement of MCB, which are as follows:

  1. One because of thermal effect of over current
  2. And the second because of electromagnetic effect of over electric current.

Thermal operation of MCB is attained with bimetallic strip. Whenever continuous over current flows through the MCB, bimetallic strip is heated and then deflects by bending. Deflection of strip releases the mechanical latch. Since the mechanical latch is attached with the operating mechanism that opens MCB contacts.

During the short circuit, sudden rise of current results electro-mechanical displacement of plunger, that is associated with solenoid or tripping of MCB. Plunger strikes trip lever resulting sudden release of the latch mechanism that opens circuit breaker contacts.

Kinds of MCB on the basis of number of poles

  1. Single Pole MCB – It offers protection for circuit where there is single phase electricity supply.
  2. Single Pole with Neutral (SPN) – It protects circuit with single phase electricity supply but neutral link does not offer any protection to the circuit.
  3. Double Pole MCB – It is also used in single phase and can replace SPN MCB but in its case neutral link gives safety to the circuit.
  4. Triple Pole MCB or Three Pole MCB – It delivers protection for the circuit with the three phase electricity supply.
  5. Three Pole with Neutral MCB (TPN) – It provides protection to all the three phases and neutral too is part of MCB as separate pole with no safety features.

Four Pole MCB – It is similar to TPN MCB with neutral MCB it possesses protective release for neutral pole. This MCB should be utilized when there is probability of high neutral current flow via circuit.

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