4 A fast-blow SMD fuse for secondary-side protection
The 0451004.NRL is a Littelfuse NANO²® 451 series surface-mount fuse rated at 4 A with a fast-blow response time, designed for board-level overcurrent protection on 125 V AC or DC circuits. Its 50 A breaking capacity at rated voltage means it can safely interrupt fault currents up to that level without rupturing — a key parameter for secondary-side protection in power supplies and DC-DC converters where the available fault current is known.
Parametric profile for the BOM engineer
Melting I²t is 3.152 — this figure governs the fuse's ability to ride through inrush current without nuisance opening; compare it against the I²t of the downstream capacitance and load to confirm coordination.
Agency approvals and compliance baseline
The 0451004.NRL carries CSA, PSE, and UL approvals — meaning it is accepted for use in equipment destined for North American and Japanese markets without additional fuse re-qualification at the system level.
Package and board-fit dimensions
The 2-SMD square end block package measures 0.240" x 0.106" x 0.106" (6.10 mm x 2.69 mm x 2.69 mm) — a common footprint that matches the NANO² 451 land pattern. The low profile keeps it clear of nearby components on a densely populated board.