1.25 A fast-blow SMD fuse for dense PCB protection
The 04511.25MRL is a Littelfuse NANO²® 451 series surface-mount fuse rated 1.25 A at 125 V AC and 125 V DC. Its fast-blow response clears quickly on high overcurrents, making it a fit for protecting power rails, input stages, and branch circuits where the downstream components can't ride through a sustained fault. The 2-SMD square end block package (6.10 x 2.69 x 2.69 mm) is a compact footprint for space-constrained boards — common in telecom line cards, battery management systems, and portable equipment where every mm² counts.
Breaking capacity and coordination
Breaking capacity is 50 A at the rated voltage — the fuse can safely interrupt a fault current up to 50 A without rupturing or sustaining an arc. For circuits with available fault current above 50 A, an upstream current-limiting device (e.g., a higher-rated fuse or breaker) is needed to keep the let-through energy within this fuse's interrupt rating. Melting I²t is 0.664 A²s — this is the energy required to melt the fuse element. It matters for inrush coordination: if the downstream load's inrush energy exceeds this value, the fuse may nuisance-open.
Approvals and temperature range
The 04511.25MRL carries CSA, PSE, and UL approvals — accepted in North American and Japanese regulatory environments.