Bussmann 20A Fiberglass Nonindicating Time Delay Midget Fuse with 250VAC Voltage Rating; FNM Series

Time-delay, nonindicating midget fuses tolerate temporary inrush currents without opening, which prevents nuisance-blowing from motor and equipment startups. Also called slow-blow midget fuses, they 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.

Midget fuses supplement the primary branch-circuit fuse or breaker to provide backup overcurrent protection for lighting, solenoid, motor, and transformer circuits. Also known as 5AG fuses, they have lower interrupting ratings than branch-circuit protectors. They are noncurrent-limiting, so they won't limit exposure to the full magnitude and duration of an overcurrent.