scope:

This part of IEC 62271 applies to three-pole units for public and industrial distribution systems which are functional assemblies of switches including switch-disconnectors and currentlimiting fuses designed so as to be capable of - breaking, at the rated recovery voltage, any current up to and including the rated shortcircuit breaking current; - making, at the rated voltage, circuits to which the rated short-circuit breaking current applies. It does not apply to fuse-circuit-breakers, fuse-contactors, combinations for motor-circuits or to combinations incorporating single capacitor bank switches. In this standard, the word "combination" is used for a combination in which the components constitute a functional assembly. Each association of a given type of switch and a given type of fuse defines one type of combination. In practice, different types of fuses may be combined with one type of switch, which give several combinations with different characteristics, in particular concerning the rated currents. Moreover, for maintenance purposes, the user should know the types of fuses that can be combined to a given switch without impairing compliance to the standard, and the corresponding characteristics of the so-made combination. A switch-fuse combination is then defined by its type designation and a list of selected fuses is defined by the manufacturer, the so-called "reference list of fuses". Compliance with this standard of a given combination means that every combination using one of the selected fuses is proven to be in compliance with this standard. The fuses are incorporated in order to extend the short-circuit breaking rating of the combination beyond that of the switch alone. They are fitted with strikers in order both to open automatically all three poles of the switch on the operation of a fuse and to achieve a correct operation at values of fault current above the minimum melting current but below the minimum breaking current of the fuses. In addition to the fuse strikers, the combination may be fitted with either an over-current release or a shunt release.