1 Scope
This part of IEC 62271
applies to three-pole units for public and industrial distribution systems which
are functional assemblies of switches composed of switches or switch-disconnectors and current-limiting fuses designed so as to be capable of
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– breaking, at the rated voltage, any current up to and including the rated short-circuit breaking current;
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– making, at the rated voltage, circuits to which the rated short-circuit breaking current applies.
It does not apply to combinations of fuses with circuit-breakers, contactors or circuit
switchers, nor for combinations for motor-circuits nor to combinations incorporating
single capacitor bank switches.
This document
applies to combinations designed with rated voltages above 1 kV up to and including
52 kV for use on three-phase alternating current systems of either 50 Hz or 60 Hz.
In this document, 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 switch-fuse combination. Different types of fuses can be combined with one type of switch, which give several
combinations with different characteristics, in particular concerning the rated continuous
currents.
A switch-fuse combination is therefore defined by its type designation and a list of selected fuses defined
by the manufacturer, the so-called "reference list of fuses". Compliance with this document of a given combination means that every combination
using one of the selected fuses is proven to be in compliance with this document.
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 can be fitted with either an over-current release or a shunt release.
NOTE In this document the term "fuse" is used to designate either the fuse or the fuse-link where the general meaning of the text does not result in ambiguity.
Fuses are in accordance with IEC 60282‑1:2020.
Devices that require dependent manual operation are not covered by this document.
Switches, including their specific mechanism, are in accordance with IEC 62271‑103 except for the short-time current and short-circuit making requirements where the
current-limiting effects of the fuses are taken into account.
Earthing switches forming an integral part of a combination are covered by IEC 62271‑102.
In addition, switches which include other functions (not covered by IEC 62271‑103) are covered by their relevant standards (e.g. IEC 62271‑102 for disconnectors and earthing switches).