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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 fuses 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.