2 A fast-blow fuse for secondary-side protection
The Littelfuse 0451002.MRSN is a 2 A, 125 VAC fast-blow fuse from the NANO²® 451 series, designed for board-level overcurrent protection where a quick open time on moderate overloads is required. Rated breaking capacity is 50 A at 125 VAC, meaning it can safely interrupt a fault current up to that level without rupturing — sufficient for secondary-side power supplies and low-power branch circuits where the prospective short-circuit current stays under that threshold. Melting I²t is 0.53, a figure used to coordinate with downstream semiconductor ratings and to estimate let-through energy during a fault event.
Surface-mount package and thermal environment
Housed in a 2-SMD square end block package measuring 6.10 mm x 2.69 mm x 2.69 mm, this fuse is intended for reflow soldering onto a PCB — the small footprint suits dense layouts where a through-hole cartridge fuse would not fit. DC cold resistance is 0.0367 ohms, which translates to about 147 mW of self-heating at rated current — negligible in most designs, but worth checking if the fuse sits in a confined pocket with no airflow.
Approvals and sourcing posture
Carries CSA, METI, and UR approvals — accepted in North American and Japanese regulatory jurisdictions without additional agency review.