R-rated MOTOR STARTER FUSES Amp-trap 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. Amp-trap R-rated fuses are rated 2R to 24R. 7.2kV fuses are UL Recognized. The 7.2kV (A072F) series has the same dimensions as the 4.8kV (A480R), allowing smaller 7.2kV equipment or 4.8kV upgrades.