Half-Blown Fuses

A question that we get relatively often, when we recommend fuse replacement rather than just continuity testing to make sure it's not "half-blown" (i.e. degraded) is:

"Is it really possible for a fuse to half-blow? I've never heard of that!"

The answer, though it may surprise many, is a resounding YES. The attached photo is of a 3.15A fuse from a Cerbo GX power supply wire, and it has "half-blown", and what we mean by that is: under 0A load, the fuse will pass full vbatt (13.6v in this case), with no voltage drop (at least, none within a hundredth of a volt).

As soon as even the smallest load (~5ma) is applied, however, voltage through the visibly melted fuse filament drops to roughly half vbatt, and the voltage drop gets worse as the load is increased. At ~2.5A, voltage through the filament has dropped to ~1.6v.

The lesson here is simply to understand that a cursory visual inspection of a glass fuse such as this (or a BMV, or CCGX, or any number of other

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