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UL Class RK1 Fuses
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UL Class RK1 fuses are more current-limiting than RK5 fuses to react more quickly to overcurrent. These 250VAC or 600VAC fuses have an interrupting rating (IR) of at least 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. These fuses are current-limiting to prevent electrical damage by disconnecting circuits before they're exposed to the full magnitude and duration of an overcurrent.