3 A fast-blow fuse for secondary-side protection
The Littelfuse 0451003.MR is a 3 A surface-mount fuse from the NANO²® 451 series, rated for 125 V AC and DC circuits with a fast-blow response time. The 50 A breaking capacity at rated voltage means it can safely interrupt a fault current up to that level without rupturing — sufficient for secondary-side protection in power supplies, battery packs, and DC rail applications where the prospective short-circuit current stays under 50 A.
Melting I²t and inrush coordination
With a melting I²t of 1.65, this fuse opens quickly on overcurrent but will tolerate brief inrush pulses below that energy threshold.
Package and board-fit
The 2-SMD square end block package measures 6.10 mm x 2.69 mm x 2.69 mm — a compact footprint for dense PCB layouts. The surface-mount terminations are compatible with standard reflow profiles.
Temperature range and approvals
Approvals from CSA, PSE, and UL cover North American and Japanese regulatory acceptance — a signal that the part has passed the relevant safety and performance testing for those jurisdictions.
Obsolete — sourcing through independent channels
Littelfuse has marked the 0451003.MR as obsolete. The NANO²® 451 series is the product family; a buyer cross-referencing a BOM line should verify the 3 A, 125 V, fast-blow parameters against any proposed replacement.