Utilization category (for a switching device or a fuse) is defined in IEC 60947-1 as the combination of specified requirements related to the conditions in which the switching device or the fuse fulfills its purpose, selected to represent a characteristic group of practical applications.
The utilization category of a circuit-breaker will determine if the circuit breaker is intended for selectivity by means of an intentional time delay with respect to other circuit-breakers in series on the load side, under short-circuit conditions.
Utilization categories are defined in table 4.
| Utilization category | Application with respect to selectivity |
|---|---|
| A | Circuit-breakers not specifically intended for selectivity under short-circuit conditions with respect to other short-circuit protective devices in series on the load side, i.e. without an intentional short-time delay provided for selectivity under short-circuit conditions, and therefore without a shorttime withstand current rating (Note 1). |
| B |
Circuit-breakers specifically intended for selectivity under short-circuit conditions with respect to other short-circuit protective devices in series on the load side, i.e. with an intentional short-time delay (which may be adjustable), provided for selectivity under short-circuit conditions. Such circuit-breakers have a short-time withstand current rating (Note 1).
NOTE Selectivity is not necessarily ensured up to the ultimate short-circuit breaking capacity of the circuit-breakers (for example in the case of operation of an instantaneous release) but at least up to the value specified in Note 2. |
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NOTE 1 The rated short-time withstand current of a circuit-breaker is the value of short-time withstand current assigned to that circuit-breaker by the manufacturer under the test conditions specified in this standard. NOTE 2 Rated short-time withstand current Icw – Minimum values (kA): Rating 2500A and lower – 12 In or 5kA whichever is greater, ratings above 2500A – 30kA. |
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References:
- IEC 60947-1 Low-voltage switchgear and controlgear – Part 1: General rules
- IEC 60947-2 Low-voltage switchgear and controlgear – Part 2: Circuit-breakers