3.15 A fast-blow in a 2-SMD square end block
The 04513.15MR is a Littelfuse NANO²® 451 series surface-mount fuse rated 3.15 A at 125 V AC and 125 V DC, with a fast-blow response time. The 2-SMD square end block package measures 6.10 mm x 2.69 mm x 2.69 mm, fitting tight board layouts where a cartridge-style fuse won't go. This is a board-mount fuse, not a cartridge type — it solders directly to the PCB and is not field-replaceable without rework. The fast-blow characteristic means it opens quickly on overcurrent, protecting sensitive downstream components from short-circuit energy.
Breaking capacity and energy let-through
Breaking capacity is 50 A at the rated voltage — the fuse safely interrupts a fault current up to that level without rupturing. The melting I²t of 1.92 tells you the thermal energy needed to clear the element; a lower I²t means faster opening and less energy passed to the load. DC cold resistance is 0.0215 ohms, so at 3.15 A the voltage drop across the fuse is about 68 mV — negligible in most low-voltage circuits but worth checking if your rail margin is tight. The approvals from CSA, PSE, and UL mean this fuse is accepted in North American, Japanese, and international equipment markets.
Obsolete — sourcing through independent channels
Littelfuse lists the 04513.15MR as obsolete. Because this is a surface-mount fuse in a standard 2-SMD square end block footprint, a parametric replacement from the same NANO² 451 series or a compatible fast-blow 3.15 A 125 V SMD fuse may fit the same pad layout — verify the footprint and I²t match before substituting.