There are two categories of LV industrial switchgear, A and B, according to IEC 60947-2
·         Those of category A, for which there is no deliberate delay in the operation of the “instantaneous” short-circuit magnetic
tripping device, are generally moulded-case type circuit-breakers, and

·         Those of category B for which, in order to discriminate with other circuit-breakers on a time basis, it is possible to delay
the tripping of the CB, where the fault-current level is lower than that of the short-time withstand current rating (Icw) of the.