20 A fast-blow fuse in a compact SMD footprint
The Littelfuse 0451020.MRSN is a 20 A fast-blow fuse from the NANO²® 451 series, rated for 65 V AC and 65 V DC. It sits in a 2-SMD square end block package measuring 6.10 mm x 2.69 mm x 2.69 mm, making it a compact overcurrent protection choice for dense PCB layouts. With a breaking capacity of 100 A at 65 V AC and 150 A at 65 V DC, this fuse can safely interrupt fault currents up to those levels without rupturing — critical for protecting downstream components in power supply or motor drive circuits.
Parametric fit and coordination
The melting I²t of 154 gives the energy needed to open the fuse under surge conditions. This value is used to coordinate with upstream breakers or fuses — the I²t of the 0451020.MRSN should be lower than the let-through energy of the upstream device to ensure selective coordination. DC cold resistance is 0.00244 ohms, so at 20 A the voltage drop across the fuse is under 50 mV — negligible in a 65 V rail and keeps power dissipation low in the enclosure. The fast-blow response time means it clears on short-duration overcurrents, suited for protecting semiconductor rectifiers or DC-DC converter inputs that cannot tolerate sustained overloads.
Lifecycle and supply posture
Approved under cURus, the fuse is accepted for use in equipment sold into North American and Canadian markets without additional agency review.