12 A fast-blow SMD fuse — what the ratings mean for the repair bench
The 0451012.NR is a Littelfuse NANO²® 451 series board-mount SMD fuse, rated 12 A continuous at 65 VAC or 65 VDC. The fast-blow response means it clears on moderate overcurrents quickly — the 47.97 A²s melting I²t tells you it handles brief inrush without nuisance opening, but a sustained overload near 20 A will trip it in under a second. The 50 A breaking capacity at rated voltage is the key fit check: this fuse safely interrupts faults up to 50 A. If your board's available fault current exceeds that — say from a stiff 65 VDC supply — you need a higher-interrupting fuse or a current-limiting element upstream.
Obsolete — sourcing the 0451012.NR now
Littelfuse lists the 0451012.NR as obsolete. No official successor order code is recorded. For a board in the field that needs this exact footprint — 0.240" x 0.106" x 0.106" (6.10 mm x 2.69 mm x 2.69 mm) 2-SMD square end block — the replacement path is through independent surplus or last-time-buy inventory. We source this part to order against an RFQ.
Temperature range and approvals
The 0.0049 Ω DC cold resistance means the voltage drop at 12 A is under 60 mV — negligible for most low-voltage rails. CSA and UL approved — the approvals cover the safety interrupt ratings for North American and Canadian installations.