What the 50 A breaking capacity means for board-level protection
The 0451.375NR is a Littelfuse NANO² 451 series fast-blow fuse rated 375 mA at 125 V AC or DC, with a breaking capacity of 50 A at rated voltage. That 50 A interrupt rating means it can safely clear a fault current up to 50 A without rupturing the package — critical for secondary-side protection in power supplies where the available fault current from the downstream bulk capacitor can hit tens of amps during a short.
Melting I²t and inrush handling
The melting I²t is 0.0425 — a figure that governs how the fuse holds up under repetitive inrush pulses. A capacitor-input filter on a 125 V rail charging through this fuse will see a surge that integrates the I²t; if the pulse energy exceeds the fuse's I²t rating, the element ages or opens prematurely. For a 375 mA fast-blow, 0.0425 is typical for protecting downstream silicon without nuisance clearing on moderate inrush.
Package, mounting, and temperature range
Housed in a 2-SMD square end block package measuring 6.10 mm x 2.69 mm x 2.69 mm, the 0451.375NR mounts on the board surface — no through-hole leads.
Approvals and compliance
The 0451.375NR carries CSA and UL approval agency marks — these certify the fuse meets North American safety standards for overcurrent protection. No RoHS or REACH compliance statement appears in the record; verify the date code against the current exemption list if your BOM requires it.