Utilization categories A and B in Circuit Breaker classification.
According to IEC 60947-2, Utilization category of a circuit breaker shall be stated with reference to whether or not it is specifically intended for selectivity by means of an intentional time delay with respect to other circuit breakers in series on the load side under short-circuits conditions. The utilization category of a circuit-breaker shall be stated with reference to whether or not it is specifically 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.
Circuit Breaker with Short Time withstand Icw capacity are Calassified as Category B (eg. ACB), and without Icw are Category A (eg. MCCB, MCB).
Utilization category A :
- Without an intentional short-time delay for selectivity under short-circuit condition and therefore without a short-time withstand current rating.
- Circuit-breakers not specifically intended for selectivity under shortcircuit 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 short-time withstand current rating.
- eg: MCCBs, MCBs., (Some MCCBs are Cat B, with Icw)
- Utilization Category A breakers are Current Limiting.
Utilization Category B
- 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.
- 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.
- eg: ACBs. (Some ACBs are Cat A, current limiting)
- Utilization Category B breakers are Selective (non current limiting)