A circuit breaker must have interrupting ratings. These are classified as rated short-circuit breaking capacities in IEC 60947-2.e rated ultimate short-circuit breaking capacity (Icu) of a circuit breaker is verified with the sequence of operations; O - t - CO.The rated service short-circuit breaking capacity (Ics) of a circuit breaker is verified with the sequence of operations; O - t - CO - t - CO.
Where, the following symbols are used for defining the sequence of operations:
- O represents a breaking operation;
- CO represents a making operation followed, after the appropriate opening time, by a breaking operation:
- t represents the time interval between two successive short-circuit operations which is as short as possible but not less than 3 min.