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In a correctly designed installation, a circuit-breaker is never required to operate at its maximum breaking current (Icu). For this reason, a new characteristic has been introduced which is the rated service short-circuit breaking capacity (Ics). IEC 60947-2 expresses (Ics) as a percentage (25, 50, 75, 100%) of (Icu) .
The rated breaking capacity (Icu) or (Icn) is the maximum fault-current a circuit-breaker can successfully interrupt without being damaged. These are very high currents of extremely low probability. In normal circumstances, the fault-currents are considerably less than the (Icu) of the circuit breaker.
On the other hand, (Ics) can be considered as high currents of low probability. It is important that (Ics) be interrupted under good conditions to ensure that the circuit breaker would be immediately ready for re-closure after the faulty circuit has been repaired.
The standard test sequence is as follows: O - CO - CO (at Ics)
Tests carried out following this sequence are intended to verify that the circuit breaker is in a good state and available for normal service.
For domestic circuit breakers, Ics = k Icn where the values for the factor "k" are illustrated on table XIV in IEC 60898.
In Europe, it is an industrial practice to use a k factor of 100% so that Ics = Icu.
The rated breaking capacity (Icu) or (Icn) is the maximum fault-current a circuit-breaker can successfully interrupt without being damaged. These are very high currents of extremely low probability. In normal circumstances, the fault-currents are considerably less than the (Icu) of the circuit breaker.
On the other hand, (Ics) can be considered as high currents of low probability. It is important that (Ics) be interrupted under good conditions to ensure that the circuit breaker would be immediately ready for re-closure after the faulty circuit has been repaired.
The standard test sequence is as follows: O - CO - CO (at Ics)
Tests carried out following this sequence are intended to verify that the circuit breaker is in a good state and available for normal service.
For domestic circuit breakers, Ics = k Icn where the values for the factor "k" are illustrated on table XIV in IEC 60898.
In Europe, it is an industrial practice to use a k factor of 100% so that Ics = Icu.
Released for:Schneider Electric Egypt and North East Africa
