1.5 A fast-blow SMD fuse for secondary-side protection
The Littelfuse 045101.5MRSN is a 1.5 A, 125 VAC fast-blow fuse in the NANO² 451 series, housed in a 2-SMD square end block package for surface-mount assembly. Rated breaking capacity is 50 A at the rated voltage — sufficient to clear a hard short on a secondary-side DC rail or low-power AC branch without rupturing the package. The 0.853 melting I²t means it tolerates brief inrush pulses from a downstream capacitor bank or a small motor start without nuisance opening, while still blowing fast on a sustained overcurrent.
What the ratings mean for the BOM line
The 125 VAC rating covers most single-phase control-voltage rails (120 VAC nominal) and the DC cold resistance of 0.063 Ohms keeps the voltage drop under 100 mV at rated current.
The 2-SMD square end block measures 6.10 mm x 2.69 mm x 2.69 mm — a compact footprint that mates with standard wave-solder or reflow profiles for the NANO² 451 series. Supplied on Tape & Reel (TR), it feeds directly into a pick-and-place machine; the reel quantity matches the standard production batch for a mid-volume BOM line.
Carries CSA and UR approvals, meaning it is accepted for use in equipment sold into North American markets under those safety standards.