400 mA fast-blow fuse for secondary-side protection
The Littelfuse 0451.400MRL is a 400 mA fast-blow fuse in the NANO²® 451 series, designed for board-level overcurrent protection where a quick open-circuit response is needed. Rated for 125 V AC and 125 V DC, it clears faults up to 50 A at rated voltage — sufficient for secondary-side protection in power supplies, battery packs, and DC rail circuits where the prospective short-circuit current stays below that threshold.
Melting I²t and cold resistance — coordination data
A melting I²t of 0.0484 A²s defines the energy needed to open the element — this number is the input for fuse coordination studies, letting you verify that the fuse clears before downstream traces or semiconductor junctions exceed their surge rating.
Surface-mount package 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 0451.400MRL mounts directly onto the PCB footprint — no through-hole staking, no separate holder.