2.5 A fast-blow in a small SMD package
The 045102.5NRL is a 2.5 A fast-blow surface-mount fuse from the Littelfuse NANO²® 451 series, rated for 125 V AC and DC with a breaking capacity of 50 A at rated voltage. That 50 A interrupt rating means it can safely clear a short-circuit fault up to that level without rupturing the package — critical for secondary-side protection in power supplies and DC bus circuits where the available fault current stays under 50 A.
What the ratings mean for your BOM
The 2.5 A current rating and fast-blow response time mean this fuse opens quickly on overcurrent but will not tolerate sustained inrush — a capacitive input or motor start that draws 4 A for 10 ms may blow it. Melting I²t is 1.029 — this is the energy to open the element. For a downstream semiconductor (diode, MOSFET) that must survive a fault until the fuse clears, the I²t of the fuse should be lower than the device's surge rating. The 1.029 figure is moderate; pair it with a semiconductor rated for at least 2 A²s surge.
Housed in a 2-SMD square end block case measuring 6.10 mm x 2.69 mm x 2.69 mm — the same footprint as the standard NANO² 451 series. The square end terminations reflow reliably with a standard solder profile; the part is symmetric, so orientation does not matter during pick-and-place.