MCBs

 

MCB stands for the Miniature circuit breaker. It is used to turn off the switches automatically in the electrical circuit to avoid the flow of extra current in case of an abnormal condition within the electrical network like overloading or a faulty condition. MCB is used as a replacement for a fuse in electrical circuits because the sensing ability of the MCB is much more reliable than the fuse in a low voltage electrical circuit. It is mainly to detect the overcurrent in the circuit-like fuse. The main benefit of the MCB over fuse is that, when circuit cut-off occurs in case of any problem, MCB doesn’t have to rewire the circuit like a fuse, it only has to turn ON the Switch (which is easy and time-saving). In other words, restoration of MCB is easy.

 

Working Principle of MCB

Thermal effect and electromagnetic effect. As the name suggests, the thermal effect works on the principle of heating. The Miniature circuit breaker can be arranged in two different ways of operation. In this arrangement, there is a bimetallic strip fitted in the MCB. When the overcurrent flows through the circuit or miniature circuit breaker (MCB), it heats the bimetallic strip and makes it bend, and causes deflection. Due to this deflection of the coil ( or bimetallic strip), an electromechanical latch occurs within the MCB, which causes the contacts of the MCB to open and turn off the switch.

While in the case of the electromagnetic effect arrangements, the short circuits cause the overcurrent to flow through the circuit quickly, which makes the plunger (associated with the solenoid coil) dislocate electromechanically in MCB. Due to this, the Plunger interacts with the trip lever, which allows the mechanical latch to open the contacts of the circuit breaker, hence the switch turning off. So these are two modes of operation for the Miniature circuit breaker.

Types of MCB

Trip curves are defined as the ability of the MCB to withstand the maximum current without turning the switch off. There are different types of Miniature Circuit Breaker (MCB) on the base of their trip curves. So that one can choose the MCB according to their requirements for a specific electrical network.

There are six different types of MCB. These are A, B, C, D, K & Z Type MCB. A Type MCB turns the switch OFF after 2-3 attempts of current overloading (as per the current rating). This type is best for semiconductor devices as it detects the short circuit more efficiently. Type B MCB turns the switch OFF after 3-5 times the current has exceeded the mentioned current rating of the circuit. It is best for the use of cable protection. Type C turns off the switch after 5-10 attempts of current overloading. Type C is best for domestic appliances. Type D turns off the switch after 10-20 times (it has been used in the high starting current application like the motors). Type K has been used to apply bulky loads as it withstands 8-12 times the initial charge.