How does mcb works

Expert Advice. Visit Other Worlds Today! What is an MCB and how does it work? A Miniature Circuit Breaker is an electromechanical device designed to protect an electric circuit from over-current - A term to describe an electrical fault caused by either overload or short circuit.

Back in the day we protected against over-current by using fuse wire indeed, we used to sell it! The principle was fairly simple - an over-current would quite literally, 'blow' the fuse wire by rapidly heating and melting it, thus breaking the electrical connection and in doing so, protected the rest of the electrical circuit.

MCBs improve on this functionality as they are usually not destroyed during over-current so are reusable. It is important to note that MCBs do not protect humans against electrical shock caused by 'earth leakage'. An MCB has three principle characteristics, Amperes, Kilo Amperes and Tripping Curve Overload Current Rating - Amperes A Overload occurs when too many appliances are put on one circuit and draw more electrical current than that circuit and cable are designed to take.

This could occur in the kitchen, for example when the kettle, dishwasher, electric hob, microwave and blender are all in use simultaneously. The MCB on this circuit cuts power thus preventing overheating and fire in the cable and terminals. Short Circuit Rating - Kilo Amperes kA Short Circuit is the result of a fault somewhere in the electrical circuit or appliance and is potentially much more dangerous than overload as the scale and speed of over current is in a different order of magnitude.

It occurs when there is a direct connection between the live and neutral conductors. Without the resistance provided by the normal circuit integrity, electrical current rushes around the circuit in a loop and multiplies the amperage by many thousand times in just milliseconds.

MCBs used in domestic installations are typically rated at 6kA or amps. The relationship between normal voltage v and typical domestic appliance power ratings mean that the over-current caused by short circuit should not exceed amps. In the event of a short-circuit, the current rises very sharply and the coil creates a magnetic field that both trips the switching mechanism and opens the contacts via a quick release mechanism.

In both cases, i. This electric arc is actually counterproductive when trying to ensure a separation of the two circuits. In order to extinguish the arc, which has a temperature of more than several thousand degrees Celsius, it must be directed away from the contacts, over the arc runners, and past the prechamber plates to the arc chamber blue area.

In the arc chamber, the formerly powerful electric arc is split into several smaller arcs until the driving voltage is no longer sufficient and they are extinguished. Restoration is easily possible by just switching it ON. Whenever continuous overcurrent flows through MCB, the bimetallic strip is heated and deflects by bending. This deflection of bi-metallic strip releases a mechanical latch. As this mechanical latch is attached with 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.

This mechanism protects from the faults arising due to overcurrent or overload and short circuit. But during short circuit condition, the current rises suddenly, causing electromechanical displacement of plunger associated with a tripping coil or solenoid.

The plunger strikes the trip lever causing immediate release of latch mechanism consequently open the circuit breaker contacts. This was a simple explanation of a miniature circuit breaker 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 mechanism. A bi-metal provides protection against overload current and an electromagnet provides protection against electric short-circuit current.

If the circuit is overloaded for a long time, the bi-metallic strip becomes overheated and deformed. This deformation of Bi-metallic strip causes, displacement of latch point. The moving contact of the MCB is arranged by means of spring pressure, with this latch point, that a little displacement of latch causes, release of spring and makes the moving contact to move for opening the MCB. The current coil or trip coil is placed so that during 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 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 moving contact separated from fixed contact in the same manner. It may be due to deformation of a bi-metallic strip, or increased mmf of a trip coil or maybe a manual operation, the same latch point is displaced and same deformed spring is released, which ultimately responsible for movement of the moving contact.