Mersen TR-RID Series, 20A RK5 Fuse; 2 in. L x 9/16 in. dia.

These 250VAC UL Class RK5 fuses are time delay and indicating. 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 a visual indicator to make it easier to identify blown fuses for replacement.

UL Class RK5 fuses provide moderate current limitation for general use applications where more current-limiting RK1 fuses aren't needed. These fuses have an interrupting rating (IR) of 200kA and are the same size as Class H and K fuses, but have a rejection feature that prevents an accidental downgrade from a current-limiting system. Their modified terminals ensure a match with the rejection clips in Class R fuse holders that prevent the installation of fuses with a lower interrupting capacity. They're typically used in newer equipment, but can also be used with a Class H fuse holder to upgrade older installations from Class H or K fuses for improved overcurrent protection. They are current-limiting to prevent electrical damage by disconnecting circuits before they're exposed to the full magnitude and duration of an overcurrent.