What this 3.5 A fast-blow SMD fuse protects
The Littelfuse 045103.5NR is a 3.5 A fast-blow fuse in the NANO² 451 series, housed in a 2-SMD square end block package measuring 6.10 mm x 2.69 mm x 2.69 mm. It is rated for 125 V AC and 125 V DC, with a breaking capacity of 50 A at rated voltage — meaning it safely interrupts a fault current up to 50 A without rupturing the package. The fast-blow response time clears overcurrents quickly, making it suitable for protecting sensitive circuits where a brief overload could damage downstream components. The 2.469 melting I²t value gives a coordination point for sizing upstream protection and predicting let-through energy during a fault.
Obsolete — sourcing path and compliance
Littelfuse has marked the 045103.5NR as obsolete. The fuse carries CSA, PSE, and UL approvals, so it meets the safety agency requirements for North American and Japanese markets.