In datasheets usually a cold resistance is given, which represents fuse resistance at low load, according to Littelfuse guide https://m.littelfuse.com/~/media/electronics/product_catalogs/littelfuse_fuseology_selection_guide.pdf.pdf

I am trying to figure out what would a "hot" resistance of the fuse be - resistance at rated current and stabilized voltage drop. Is it safe to assume it should be higher than cold resistance, and is there a rule of thumb that can help with its estimatation?


Yes, hot resistance will generally be higher than cold resistance. And it will be higher at higher ambient temperature.

A decent fuse datasheet will list the cold resistance and the hot voltage drop at room temperature. You can calculate the hot resistance by dividing the voltage drop by the rated current.

Normal operation will likely be somewhere between those two values.

For example, a GDC-1A Buss fuse has a voltage drop of 87.5mV typical at 20°C Ta and 1A, so the hot resistance is 87.5m\$\Omega\$. The cold resistance is typically 75.7m\$\Omega\$.

Sometimes a figure is quoted as a ratio of hot to cold.

  • \$\begingroup\$ It seems that Littlefuse doesn't provide this info in their datasheet. They only give cold resistance. I sent an email to ask for some info. In any case, this seems to be the info that should be provided by the fuse manufacturer - datasheet, technical specs or similar. For this reason I will mark your answer as acceptable. \$\endgroup\$
    – DenR
    Oct 5 '20 at 12:41

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