mccb

Ultimate Breaking Capacity means that the MCCB can break the rated ultimate breaking current for two times and after that the MCCB is useless (It cannot even be used for carrying rated current); The duty cycle is: O-t-CO

Service Breaking Capacity means that the MCCB can break the rated service breaking current for 3 times (The Duty Cycle is: O-t-CO-t-CO) and after that it can still be used as a switch - that is, to make, carry and break normal rated currents and overload currents. However, it cannot any further be used for making or breaking any short circuit currents. So, till replacement comes, this MCCB can be used as a Switch - of course, with some back-up Short Circuit Protective Device such as a Fuse.

Standards specify that Ics can be a percentage (25% or 50% or 75% or 100%) of Icu.