630 mA fast blow SMD fuse — the Littelfuse 0451.630NR
The 0451.630NR is a 630 mA fast-blow surface-mount fuse from Littelfuse's NANO²® 451 series, housed in a 2-SMD square end block package measuring 6.10 mm x 2.69 mm x 2.69 mm. Rated for 125 VAC and 125 VDC, with a breaking capacity of 50 A at rated voltage — sufficient for clearing faults on low-voltage DC rails and AC control circuits without cascading upstream. The 0.1381 melting I²t figure tells you the energy required to open the fuse element — a key parameter for coordinating with downstream semiconductor protection and for sizing the fuse to survive inrush without nuisance opens.
Obsolete — sourced through independent channels
Littelfuse lists the 0451.630NR as obsolete. For existing BOM lines, this part is available through independent distribution — quantities are confirmed at RFQ, and each lot is verified for authenticity and compliance. If you are qualifying a replacement, the NANO²® 451 series shares the same footprint and ratings across current values; a 630 mA fast-blow alternative from a different series would require board-level re-qualification for the I²t and voltage derating.
Approvals and operating envelope
Carries CSA and cULus approval — accepted for North American and Canadian equipment listings where branch-circuit protection is not required.