MERSEN R-rated fuses are current limiting, high interrupting rating fuses intended for the short circuit protection of medium voltage motors and motor controllers. R-rated fuses are back up fuses that have a minimum interrupting rating, and must be coordinated with overload relays in combination motor starters. The motor starter manufacturer generally specifies the R-rated fuse size. These fuses come with a 3 (size D) or 4 (size E) in diameter barrels with ferrules and are mounted in spring reinforced clips.