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If a given circuit (containing a fuse) operates perfectly and continuously, will there come a time when the fuse simply stops working due to age and wear (wear from passively passing current throughout the years)?

More concretely, I have two identical fans, bought at the same time and used at about the same rate, and the fuses in both have failed within a similar timeframe. I wonder if it is the shelf life of the fuse at fault (the fans have been used for 10 years), or whether it is a defect with the fan motor design?

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    \$\begingroup\$ I'd guess more related to accumulation of dust on fan blades and dust in the bearings (which are probably not really good roller bearings but something less long-lasting) eventually leading to increased current draw under the added friction and load. I just dismantled and repaired a motor that blew an internal fuse... but it was installed in 1970 and came from a very good manufacturer. Still, it eventually gave out after 50 years and I had to fix it. It's running fine, now. I doubt in your case that the fuse "wore out" in 10 years. They probably did their job. \$\endgroup\$
    – jonk
    Commented Aug 20, 2021 at 4:16
  • \$\begingroup\$ The answer is yes but evidence is hard to find. Hell, fuses go bad on the shelf let alone in production. \$\endgroup\$
    – Passerby
    Commented Aug 20, 2021 at 4:18
  • \$\begingroup\$ @Passerby Seriously? (That's not been my experience. But I'm sure you have much more than I do on this score.) \$\endgroup\$
    – jonk
    Commented Aug 20, 2021 at 4:19
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    \$\begingroup\$ What if it is just normal wear and tear and degradation of all the other parts except for the fuse? The fan has a motor I suppose, so lubricants gather dust and dry out adding friction, and the startup capacitor may have started to fail. A fan may not be rated to handle more than 10 years of usage in your conditions. \$\endgroup\$
    – Justme
    Commented Aug 20, 2021 at 4:27
  • \$\begingroup\$ I see, thank you all for the insights. @jonk and Justme, in the case where dust accumulation and resulting friction is the underlying cause, is cleaning the motor and greasing the bearings a good repair? Or did running under said conditions (before finally triggering the fuse) damage / wear down the wires of the motor's winding? \$\endgroup\$
    – Jet Blue
    Commented Aug 20, 2021 at 5:06

2 Answers 2

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Well, a fuse wire has to heat and melt when the load goes over limit. So, it is intentionally made thin. However, this means that under normal load, it will be warm. Over time, this leads to oxidation based degradation and perhaps also a bit of evaporation. There's also the degradation near the area of solder. Over time, this leads to gradual reduction of the current rating of the fuse. Eventually, the fuse blows at the normal load. Especially at startup, when the load is usually higher than steady state. Someday, that blows the fuse. If the rest of the equipment lasts that long !

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A high inrush current stresses the fuse filament each time you power up. Over time, the filament can fracture and fails. You can usually tell if this is the case as the filament is essentially intact but broken. If the fuse fails from overload, the filament melts. If it is a gross overload, it vapourises.

I think the effect might be called ‘magnétostriction’ - i might need to be correct on that.

I’ve observed this type of failure in crt colour tvs and monitors where the degauss cycle pulls a high initial current. I’ve also had it with large stepper motor drivers.

One possible solution is to use a sand filled hrc fuse. It is my understanding that the sand supports the filament and lessens the stress

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