750 mA fast-blow in a 2.69 mm square body
The 0451.750MRSN is a 750 mA, 125 VAC fast-blow fuse from Littelfuse's NANO²® 451 series. It clears overcurrents quickly, with a 50 A interrupting rating at the rated voltage — enough to handle a hard short on a 125 VAC secondary circuit without the fuse casing rupturing. The 0.185 melting I²t tells you the energy needed to open the element — useful when sizing the fuse against inrush from a capacitive input or a motor start. A downstream DC-DC converter with a 100 µF input cap at 48 V will need a fuse with I²t headroom above the capacitor's charge pulse; this 0.185 figure lets you check that margin before the first prototype.
Surface-mount footprint and temperature range
Housed in a 2-SMD square end block package measuring 6.10 mm x 2.69 mm x 2.69 mm, the 0451.750MRSN mounts directly to the PCB — no holder, no through-hole. The ceramic body and silver-plated end caps handle the thermal cycling without fatigue cracking — common in outdoor telecom or engine-bay auxiliary circuits.