Circuit Breaker Utilization Categories (IEC 60947-2)

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.

Table 4 – Utilization categories
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.

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.

References:

  1. IEC 60947-1 Low-voltage switchgear and controlgear – Part 1: General rules
  2. IEC 60947-2 Low-voltage switchgear and controlgear – Part 2: Circuit-breakers

About the Author

Ver Pangonilo
A Filipino Engineer, Registered Professional Engineer of Queensland (RPEQ) - Australia and Professional Electrical Engineer (PEE) - Philippines with extensive experience in concept select, front-end engineering, HV & LV detail design, construction and commissioning of Hazardous and Non-Hazardous Area electrical installations in water and waste water pipeline and pumping facilities, offshore platforms, hydrocarbon process plants and pipelines including related facilities. Hazardous area classification and design certification (UEENEEM015B, UEENEEM016B, UEENEEM017B).
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