These 600VAC UL Class RK5 fuses are time delay and nonindicating. They tolerate temporary inrush currents without opening, which prevents nuisance-blowing from motor and equipment startups. Also called slow-blow Class RK5 fuses, these 200kA IR fuses open to disconnect an electrical circuit when exposed to sustained loads and short circuits. They have no indicator for identifying a blown fuse, so they're sometimes used with an indicating fuse block or cover.