Fast-blow SMT fuse, now in surplus channel
The Littelfuse 04511.25MR is a 1.25 A fast-blow surface-mount fuse from the NANO² 451 series, rated for 125 V AC and DC with a breaking capacity of 50 A at rated voltage. lists this part as obsolete, meaning original factory production has ceased; supply now runs through independent surplus and broker channels, with quantities and pricing confirmed per RFQ.
Parametric fit and board-level considerations
Melting I²t is 0.664 — this value governs the fuse's ability to withstand inrush currents without nuisance opening; a downstream capacitor bank or motor start with a surge exceeding this I²t threshold will blow the fuse on power-up. DC cold resistance measures 0.078 Ω, which at 1.25 A produces roughly 0.12 W of self-heating — negligible in still air but relevant when the fuse is packed inside a sealed module with no convection path. Package is a 2-SMD square end block measuring 6.10 mm x 2.69 mm x 2.69 mm — the ceramic body and end-cap construction are designed for the 50 A interrupting rating; a standard 1206 or 2410 footprint will not match this form factor. Approved by CSA, PSE, and UL — the UL listing is the one most North American safety reviewers will look for; the PSE mark covers Japanese market compliance.
Obsolete — sourcing this fuse today
Available through independent distribution; lot traceability and manufacturer date codes are confirmed at the time of RFQ. No pin-compatible drop-in replacement from Littelfuse is documented, so a BOM-line substitution requires verifying the same package footprint and I²t characteristic.