Mersen Protistor® 14x51 Type gR Fuses From Mersen, a range of cylindrical Ultra-rapid fuses available in various current ratings with or without built-in strikers. These 14 x 51 Protistor® fuses are designed to protect power semi-conductors which comply with IEC 60269-1 and -4. Features and Benefits • gR class • With or without striker • Improved safety and protection • Distribution circuit fuses • IEC standard 60269-4 compliant • Clearing all overloads Standards • IEC 60269-4 • UL 248-13 • CCCD GB 1539.4