The switch disconnectors series FKN12 are increasingly adopted in MV installations, owing to their superior interrupting features and to their capability to withstand the short-circuit currents which occur mainly as consequences of faults in distribution networks. The versions combined with HRC fuses are particularly suitable for the protection of distribution transformers up to 1250 kVA The use of FKN12, designed for installation in compartmented switchboards have the following advantages: -Full segregation between the busbar compartment and the cable compartment, with switch disconnector in both “closed” and “open” position. -The moving contact, of the sliding vertical type, can be easily checked and cleaned with live bus-bars and earthing switch (ES) closed. -No adjustment is needed in the tripping mechanism of the switch fuse combination and of the ES: they are built together in a single unit, which is adjusted and checked during assembly in the factory, before the final test.