Based on IEC 60947-2 (LV switchgear and controlgear - Part 2: Circuit breakers):
In (Rated current)
The rated continuous / uninterrupted current that the circuit breaker can carry.
Icm (Rated short-circuit making current)
The short-circuit current that the circuit breaker can withstand as it is closing where the act of closing initiates the fault.
Icu (Rated ultimate short-circuit current)
The maximum symmetrical short-circuit current the circuit breaker can interrupt.
Ics (Rated service short-circuit current)
The breaking capacity such that the circuit breaker is tested to carry its current continuously. The test sequence verifies that the breaker can be returned to service. Ics is the maximum current the breaker can interrupt multiple times and be returned to service without being damaged and is expressed as a % of Icu.
Icw (Rated short time withstand current)
This is the steady state symmetrical fault current the breaker has to be able to carry for a duration of 0.05s to 3s without exceeding its thermal integrity.
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