Icu, Ics, Icw: what a breaker rating actually promises
Four short-circuit ratings, one selectivity limit current, and the difference between a breaker that survives a fault and one that is finished by it - per IEC 60947-2.
The rating you quoted may be the wrong one — A breaker carries several short-circuit ratings, and they are not interchangeable. IEC 60947-2 defines each one by the test sequence behind it.
The four ratings — IEC 60947-2:2016, 4.3.6.2.2 and 4.3.6.2.3.
Icu clears the fault. Ics clears it and stays in service. — Selecting a device on Icu alone is legitimate only if you accept that a fault at that level may end the breaker's working life. On an incomer or any circuit that has to be re-energised, the number that matters is Ics.
Category A or category B
Selectivity limit current Is — Is is the current at the intersection of the load-side device total operating characteristic and the upstream device tripping characteristic. Below it selectivity is ensured; above it the upstream device may start to operate too (IEC…
What the standard requires to be marked — IEC 60947-2:2016, 5.2. A submitted datasheet missing these is not comparable with another one - and the reference temperature is the line that quietly moves a thermal setting in a 50 deg C plant room.
The rating is at a voltage — Every breaking capacity is declared "at the corresponding rated operational voltage Ue". The same frame commonly has one Icu at 415 V and a lower one at 690 V. Reading the headline number without its voltage is the most frequent way this…