Current Limiting Fuses

A current-limiting fuse is one that opens and clears a fault in less than 180 electrical degrees, or in other words, within the first half electrical cycle (0.00833 seconds). The total destructive heat energy (I2t) to the circuit and its components is greatly minimized as a result of using current-limiting fuses.

This selection consideration now involves determining the degree or level of current limitation required to properly protect a given device or system upon startup or short circuit. It is also important to point out that matching fuse holders and/or fuse blocks must reject non-current-limiting fuses and accept only current-limiting fuses of the stated UL Class.

Current limiting fuse containing a resistor inside

F2525-ND (0313.031HXP) is an example fuse we distribute which does contain a 430 Ohm resistor inside, although our product page image does not reflect this as product photos are for reference only.

The datasheet for this fuse also doesn’t show the resistor inside, but does list the “Cold Resistance”:

The current limiting resistance can also be found on the Digi-Key site in the “Product Attributes” section on the product page:

Cold resistance is the resistance obtained using a measuring current of no more than 10% of the fuse’s nominal rated current. Values shown in this publication for cold resistance are nominal and representative. The factory should be consulted if this parameter is critical to the design analysis. Hot resistance is the resistance calculated from the stabilized voltage drop across the fuse, with current equal to the nominal rated current flowing through it.

See also:
Littelfuse Application Guide
Littelfuse - Fuseology
Simple Inrush Current Limiting in Power Applications
Fuse I2T Rating, Melting Point, and Interrupt Rating
Digi-Key Temperature Sensors - NTC Thermistors
Digi-Key Inrush Current Limiters (ICL)
Digi-Key Fuses Selection