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I want to replace a blowed fuse 125V/4A but it is rare to find them. Can I use instead a 250V/4A ?

I read at https://www.mojotone.com/support/Knowledge-Base/Is-it-ok-to-replace-125v-glass-fuses-with-250v-glass-fuses-of-the-same-rating that

Fuses are designed to protect over-current, not over-voltage. Therefore as long as the fuse amperage is sized appropriately and as long as your fuse voltage meets or exceeds your application voltage the fuse will safely protect.

So, its ok to replace with 250V/4A ?

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Maverick
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  • Why did this fuse blow? What's stopping the replacement blowing if you replace it? – D Duck Dec 29 '18 at 11:29
  • The problem it self was fixed. – Maverick Dec 29 '18 at 11:31
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    Generally yes, higher voltage rating on the fuse is not an issue. There is a small risk that the time delay/slow versus fast blow differs between them, but unlike to cause any explosive fire or catastrophe. – winny Dec 29 '18 at 12:51

2 Answers2

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Fuses are used for over-current protection, first please diagnose the mistake what causing the fuse to blow (like any shortages, overloading or some faults) and solve that before you replace new fuse.

As long the voltage of fuse is more than the system voltage. you can use it.

Since, what you are saying is right.. fuses protects the system/equipment from over-current not over-voltage.

Electron
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    As long as..... *the breaking capacity (rupture current) of the replacement fuse, for the current type (AC or DC) used, also meets or exceeds what is specified for the application* ! In this case, you are replacing a non sand filled fuse in presumably an AC application, so no problem - replacing a sand filled fuse from a DC circuit with a plain hollow glass fuse of the same size would be a bad mistake. – rackandboneman Dec 30 '18 at 14:19
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Yes.

The voltage rating on a fuse tells you how high a voltage it can interrupt without arcing or otherwise allowing current to continue to flow after the fuse blows. A fuse of equal or higher voltage rating is fine as a replacement (after fixing whatever caused the old fuse to blow). DC applications require DC-rated fuses.

The conditions that will cause a fuse to blow are solely related to current (and time). A replacement fuse needs to match current rating and slow-blow or not; no more and no less, so it doesn't blow spuriously and doesn't allow more current than desired without blowing. A slow-blow fuse will allow some specified over-current for some guaranteed amount of time without blowing; useful for cases with high startup current.

All fuses depend on time, though, and slight over-currents might take a long time to blow, if ever. (The 4A rating is I think the max current at which it's guaranteed not to blow given unlimited time; vendors provide graphs of current vs. time to blow with some uncertainty range I think; some other answers have included examples. Something like 4.1 amps in a 4A fuse might have an expected time-to-blow range that includes multiple minutes and never.)

Fuses are similar to a switch or relay that has to be able hold off a high voltage across itself. Interrupting a high current with an inductive load can create transient high voltages, which could create an arc. When a fuse first melts apart, you presumably do get some arcing over the tiny initial gap, but it presumably extinguishes quickly as more metal melts and the gap gets too long.

Fuses only rated for AC normally depend on the zero-crossings (every half-cycle) of the voltage/current to extinguish the arc, and aren't safe for DC usage, especially at higher voltages.

Peter Cordes
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