Active production, field-swappable SMD fuse
The 0451005.MRSN: Breaking capacity is 50 A at the rated voltage — enough to safely clear a fault on most low-voltage DC rails or AC control circuits without the fuse casing rupturing.
What the ratings mean for your board
The 5 A current rating is the continuous current the fuse carries without opening at 25 °C ambient. The fast-blow response time means it clears quickly on overcurrent — useful for protecting sensitive downstream silicon where a slow-blow fuse would let the fault energy through. Melting I²t is 5.566 — this is the energy needed to melt the fuse element. If your circuit has a capacitor inrush or motor start surge, compare the pulse energy to this figure to avoid nuisance openings. DC cold resistance is 0.0125 ohms. At 5 A the voltage drop is about 62.5 mV, and power dissipation is roughly 0.31 W — negligible for most designs, but worth checking if the fuse sits in a tightly sealed enclosure with no airflow.
Package and board-fit
Housed in a 2-SMD square end block package measuring 6.10 mm x 2.69 mm x 2.69 mm.
Temperature range and approvals
Carries CSA, METI, and UR approvals, so it is accepted in North American and Japanese regulatory jurisdictions without additional testing.