1 A fast-blow fuse for secondary-side protection
The Littelfuse 0451001.MRL is a 1 A fast-blow surface-mount fuse from the NANO² 451 series, rated for 125 V AC and DC circuits. The fast-blow response clears quickly on high-fault currents, making it a fit for short-circuit protection rather than slow overload ride-through. Breaking capacity is 50 A at rated voltage — the fuse can safely interrupt a fault up to that level without rupturing or sustaining an arc. Below that threshold, the element opens cleanly; above it, the fuse may not clear and the fault propagates upstream.
Package and board-fit constraints
Housed in a 2-SMD square end block package measuring 6.10 mm x 2.69 mm x 2.69 mm, the 0451001.MRL is a surface-mount device intended for automated pick-and-place assembly. The square end-block footprint mates with standard solder pads for this fuse class — no special cutouts or through-hole tooling needed. DC cold resistance is 0.153 ohms, which sets the voltage drop at rated current at roughly 153 mV.
Temperature range and approvals
The fuse does not derate significantly across this band — the melting I²t of 0.459 stays consistent, so coordination with upstream breakers or fuses holds across temperature. Approved by CSA, PSE, and UL — the fuse is accepted in North American and Japanese regulatory jurisdictions without additional agency review. No AEC-Q rating is listed, so it is not formally qualified for automotive stress tests, but the temperature range overlaps with Grade 1 requirements.
Sourcing and lifecycle posture
The NANO² 451 series includes other current ratings in the same package and footprint — a BOM change to a different amp rating requires verifying the I²t coordination and voltage drop, not just the current number.