7 A fast blow SMD fuse — NANO² 451 series
The 0451007.MRSN is a 7 A, 125 VAC rated fast-blow fuse from Littelfuse's NANO² 451 series, housed in a 2-SMD square end block package for surface-mount assembly. Breaking capacity is 50 A at rated voltage — sufficient for clearing low-to-moderate fault currents in secondary-side protection of power supplies, lighting ballasts, and industrial control boards.
Inrush handling and cold resistance
Melting I²t is 10.32 A²s — this sets the energy threshold the fuse absorbs before opening; a downstream capacitor bank charging at turn-on must stay below this integral to avoid nuisance blowing. DC cold resistance is 0.009 Ω, so at 7 A the I²R loss is under 0.5 W — negligible thermal contribution in still air on a standard FR-4 board.
Approvals and temperature range
Approved by CSA, METI, and UR — the fuse carries the marks needed for equipment sold into North American and Japanese markets.