IEC 60420:1990

This standard applies to three-pole units for public and industrial distribution systems which are functional assemblies of switches including switch-disconnectors and current-limiting fuses and thus able to interrupt: -any load current up to the rated breaking current of the switch; -any over-current up to the rated short-circuit breaking current of the combination by which automatic interruption is initiated. This standard applies to combinations designed with rated voltages above 1 kV and below 52 kV for use on three-phase alternating current systems of either 50 Hz or 60 Hz.