Active protection for 125 VAC secondary circuits
The Littelfuse 0451.250MRSN is an active-production NANO²® 451 series SMD fuse rated for 250 mA continuous current at 125 VAC, with a DC cold resistance of 0.5765 Ohms and a fast-blow response characteristic. Its 50 A breaking capacity at the rated voltage means it safely interrupts a fault current up to that level without rupturing the package — a critical spec for secondary-side protection in power supplies where the prospective short-circuit current can exceed the fuse's interrupt rating if undersized.
0.0158 I²t coordinates with downstream traces and FETs
The melting I²t of 0.0158 A²s tells you the energy needed to clear the fuse element — this number drives the coordination study with the PCB trace width and the silicon die area of any downstream MOSFET or diode that must survive a fault before the fuse opens.
2-SMD square end block for pick-and-place
Housed in a 2-SMD square end block package measuring 6.10 mm x 2.69 mm x 2.69 mm, the 0451.250MRSN uses the standard NANO² footprint that mates with common Littelfuse pad layouts — no custom land pattern needed. Supplied on Tape & Reel (TR), it feeds directly into a high-speed pick-and-place machine without a reel-change interruption for most reel capacities.
CSA and UR approvals cover North American panel builds
CSA and UR approval agency markings are listed — the fuse carries the recognized component mark for UL 248-14 and the corresponding CSA standard, so it passes the acceptance gate for most North American industrial and commercial power supplies without a separate agency review.