MCCB Ratings

Manufacturers of MCCB provide technical specifications for each circuit breaker model. In order to select the correct MCCB for the necessary application, it is important to understand these ratings.

Rated Frame Current (Inm): This is the maximum current value of which the MCBB is designed and also determines the physical dimensions of the device. It defines the upper limit of the adjustable trip current range.
Rated Current (In): This is the current value above which overload protection is tripped. It is an adjustable range rather than a fixed value that defines the upper limit of the rated current range.
Rated Insulation Voltage (Ui): This is the maximum voltage the MCCB can resist in laboratory tests. To provide a margin of safety during field operation, the value is higher than the rated working voltage.
Rated Working Voltage (Ue): This is the continuous operation voltage for which the MCCB was designed. The value is typically close to or equal to the standard system voltage.
Operating Short Circuit Breaking Capacity: (Ics): This is the highest fault current an MCCB can trip at without being damaged permanently. It will be reusable after interrupting a fault if it does not exceed this value.
Ultimate Short Circuit Breaking Capacity (Icu): This is the maximum fault current the MCCB can clear. If the current exceeds this value, the MCCB will be unable to trip and it is up to another protection mechanism with a higher capacity to take over. If a fault occurs that is above the Ics but below the Icu, the MCCB will be able to interrupt it but will need to be replaced due to damage suffered.

Mechanical Life: This is the number of times the MCCB can be operated manually before it fails.
Electrical Life: The number of times the MCCB can trip before it fails.