Littelfuse medium voltage fuses are silver element, silica sand, nonexpulsion design, current-limiting type devices. When properly applied, they are designed to carry their nominal current rating continuously without fatigue failure. This means that the fuse will not age, become brittle, or deteriorate under the most severe duty cycling.
When talking current-limiting medium voltage fuses, there are two basic types: general purpose and back-up. General purpose fuses have the ability to interrupt both large and small short-circuits down to currents which would cause the fuse to open within one hour. They are used to provide short-circuit protection for transformers, switchgear, and similar equipment.
Backup fuses are designed to protect only against high fault currents and must be used in series with equipment which provides the circuit’s required overload and low value short-circuit protection.
Medium voltage E-rated fuses are considered general purpose fuses. Their mounting dimensions permit them to be installed in a wide variety of medium voltage switches, in pad-mounted transformers, and at other similar locations. R-rated MV fuses are specifically designed to provide short-circuit protection for medium voltage motor controllers and associated equipment.