MCB(Miniature Circuit Breaker) is a series of circuit breaker that belongs to the advanced level of technology. MCBs provide protection against over loads and short circuits and save wires, cables and equipments.
They are used as protective functions against shortage and overloading, and are used in lighting distribution system in industries, commerce and dwelling, and in protecting fractional electric motors. MCBs have many merits of high protective grade (up to IP20), high breaking capacity, good reliability of sensitive action, convenient multi-pole assorting, long life etc. They are mainly adapted for the circuits of AC 50Hz, 230V in single pole, 400V in double, three or four poles for protecting overload and shortage. Meanwhile, they are also used in turning on or off the electric apparatus and lighting circuits under normal conditions.
Different type of MCB's
(This picture is contributed by "Mishta")
MCB types according to Magnetic trip:
- Type B-This type of MCB trips from 3 to 5 times when there is full load current.
- Type C- This type of MCB trips from 5 to 10 times when there is full load current.
- Type D- This type of MCB trips from 10 to 20 times when there is full load current.
- MCBs have (6A, 10 A) etc current ratings above which their function start to open or trip and give protection to the equipment and human being.
- 6KA fault level of MCB is sufficient enough for general consumer unit, where as 10 KA and above fault level of MCB is sufficient for industrial units.
- MCBs prevent the accidental overloading of the cable. The speed of the MCB tripping will vary with the intensity of the overloading and depends upon the use of a thermal device in the MCB.
- MCB should be capable to give protection against heavy faults caused by short circuits. Kilo Amps (KA) is the unit of MCB given in the short circuit conditions.
- MCBs prevent magnetic fault problems and operate in 1/10 of a second when the fault reaches predetermined level.
Things to remember:
- At the time of installing of MCB, ensure that the MCB does not give unwanted tripping despite of compliance with the Wiring Regulation and without over loading.
- Install proper type of MCB according to load, sometimes, for electric motors or low voltage lighting, the use of a type B MCB may give unwanted tripping. Installing of type C MCB solves this problem.
- Type D MCB may be installed after consultation with qualified engineer to avoid any problem later on.
- Generally, type B MCB is sufficient for normal resistive loads. However, in some commercial and industrial units where at the time of starting, either motors or special lighting or data equipment may adversely affect the MCB, in such case it is necessary to use type C characteristic MCB.
- In industrial units where compressor motors are used, if type B and C of MCB are not able meet the requirements then use of type D MCB is necessary.
Caution: The characteristics for these MCBs may make compliance with the Wiring Regulation difficult without a change in the specifications.