25.8kV FERRULE MOUNTED FUSES 9F60 series E-Rated fuses have 2 or 3 Inch diameter barrels with ferrules and are mounted in spring reinforced clips. Some can be used outdoors. The unique time-current characteristic of Mersen E-Rated fuses allows them to be closely sized to transformer full-load rated current, as recommended by IEEE guidelines, without being affected by normal magnetizing inrush current..