Molded Case Circuit Breaker

What is MCCB ( Molded Case Circuit Breaker ) ?

It is a mechanical device ( BS 4752 ) to be used to connect and disconnect the circuit in normal and abnormal.Current rate for regular MCCB up to 3000 ampere.

It is only available in a 3 pole only, usually for a system that has a high ampere ratings in three ( 3 ) phase systems.For those who have ampere ratings than 400 ampere, the safety interlock system is prepared for security purposes because the current system are high.

There are two ( 2 ) types of MCCB commonly used in industry, it was: –

1) Magnetic Type

It works by using a solenoid system, in the event of excess current, current transformer will send a signal to solenoid to activate the plunger mechanism that will actuate and break the circuit.mechanism commonly used is the force of spring or hydraulic system to activate.Usually the ambient temperature affects the time interval for it is active but has no impact on current rates for MCCB.This system is active immediately and can not be adjusted to determine the time interval circuit

2) Thermal type

It is commonly used in the distribution panel, it works to break the circuit caused by a short circuit and over current.its operating system is based on the temperature resulting from the current flow in the core conductor.when the current through the core conductor is very high, so high temperatures will be produced.Two metals in the core conductors will react and will enable the system to determine the mechanism of the circuit.This system is active with the interval of time and can be adjusted to suit the circuit

Important features of the MCCB

1)  Icw = Rated short withstand current

2) Icu = Rated Ultimate short circuit breaking capacity

3) Ics = Rated service short circuit breaking capacity

For INCOMING FEEDER system,the suitable rated service short circuit

( Ics ) is 100 % setting.

For ALL OUTGOING FEEDER system,the suitable rated service short circuit

( Ics ) is 50 % setting

For more details setting,please refer manufacturing manual for MCCB.


  1. bhavesh jani says

    i want to know littlebit about power system protection and switching device . will u pleas help me.

  2. Tawheed Ahmad says

    HI SIR
    The formula for mccb sizing is same to that of mcb?
    plz conform it to me

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