Friday, 10 April 2020

Miniature Circuit Breaker (MCB)- Construction, Working, Advantages, Applications.

● Miniature Circuit breaker. It also called as MCB. A circuit breaker is a switching (On/Off/Trip) device that is used for switching on and off the load and for inturreting the circuit under the fault condition.

● Circuit breaker make or break a circuit doing normal conditions. During the unhealthy conditions they break the circuit to prevent the spread of fault to other equipments.

Miniature Circuit Breaker
Miniature Circuit Breaker

● Circuit breaker is safety device used to protect your electrical appliances at home in case of short circuit or any other cause for excessive current. It operates manually as well as automatically.

● Circuit breaker have to be simple, because they are a minor safety measure in common haosehold and in the electrical grids.

Construction of MCB

There are any parts are arranged in circuit breaker.

Construction of MCB
Construction of MCB 

External casing
External casing is the insulation which hold all the components and protects them from the durt and dust.

Knob is the switch which used to turn on and off the MCB.

There are two contacts inside the circuit breaker one is fixed contact and other is movable contact.
To hold the contacts under the spring tension when MCB is ON position.

● Bimetallic strip
The bimetallic strip used to offer delayed overload protection by sensing the flow of current greater than its rated current.

Solenoid provides instantaneous protection against short circuit by releasing the mechanical latch.

Arc chutes
It is used for the splitting and quenching the arc.

Working of MCB

● There are two types of operation of an MCB. The first depends on the thermal effect of overcurrent.

● Thermal Effect
When the over current flows through the MCB the bimetallic strip present in MCB owing to the thermal expansion of metals is heated and deflects by bending.

● That deflection in the strip releases a mechanical latch and this operates the contacts of the MCB to connect the fault circuit.

● Electromagnetic Effect
In the short circuit conditions the fault of sudden rising of current causes electromechanical displacement of the plunger connected with the tripping coil or the solenoid of MCB.

● Then plunger strikes the trip level with the causing of immediate release of the latch mechanism consequently so the circuit breaker contacts gets open.

Advantages of MCB

● We can identify tripped MCB even in darkness.

● It gives trip free mechanism- cannot be switched back on while fault exists.

● It also acceptable as a isolator.

● There is no any wire to replace like fuse.

● Normally it do not requires replacement.

● They act and open the circuit in less than 5 milliseconds.

● Supply is restored by resetting it again.

● It requires less maintenance and it is more reliable.

Disadvantages of MCB 

● The MCB is costly than fuse.

● The cost of MCB distribution board is greater than desirable fuse board.

Applications of MCB

● New constructions uses MCB instead of the older type fuses.

● It is designed to protect the houses from circuit overload.

● Can be used for ground fault or arc fault mechanisms.

● Domestic appliances, power supplies, lighting circuits and motor circuits etc.


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