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Old 25th June 2010, 02:54 AM   #1
a.wayne is offline a.wayne  United States
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Default Fuses - WTH

Can anyone clear the smoke behind fuses and there confusing ratings ...

When trying to order and buy fuses they are rated @ 32v, 125 V, 250 V
Yet most 125 V amplifiers use 15amp/32 v fuses ...

Worst most suppliers have 250v/15,10 ,5 amp etc fuses for 120v equipment , what gives and how can a 32v15amp fuse be the same and not different from a 125/15amp fuse and why stock 240/250v fuses here in the states ?

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Old 25th June 2010, 03:31 AM   #2
Enzo is offline Enzo  United States
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The voltage rating is about how high a voltage the blown fuse can break without arcing across the gap. The question is not why stock 250v fuses, it is more why bother having 125v fuses when the common 250v fuses will cover all the 125v applications and more.

You can always use a higher voltage fuse than you need, just as you can use wire insulation of higher voltage rating than you need.

32v fuses are more common in the higher current values, they use them in cars. As a rule, they work just fine in 120VAC applications, whether it is officially correct or not, so they do it. Just easier to find than the 250v ones.

Fuses operate on current, the voltage across a good fuse is extremely low after all. SO the fuse voltage rating has no effect on the blowing or not blowing.

I rarely see 125v fuses as loose pieces. I see them in original equipment, mainly imports. I would guess that the lower voltage fuse might cost a tiny fraction of a cent less to make than the 250v versions. When you make fuses by the millions, those fractions can add up. SO in my opinion, that is why 125v fuses are made at all.
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Old 25th June 2010, 04:35 AM   #3
a.wayne is offline a.wayne  United States
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Hello ,

thanks for the response , it does get con-fusing ..

I do notice the 32V has a thicker element for the same amp rating as the 250 v fuses..

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Old 25th June 2010, 07:26 PM   #4
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When a fuse blows, it has to be able to "clear" the arc across the gap. The higher the voltage the longer the gap needs to be. While a 32V fuse probably will work with 120V, what happens when a power company failure sends 440V do that 120V line? That poor little 32V fuse won't clear the high voltage arc.
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Old 26th June 2010, 04:36 AM   #5
Enzo is offline Enzo  United States
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Yep. That's the tradeoff.

I'd have to say that that 440v would probably kill the amp faster than a fuse could blow anyway.

Fuses aren't really there to protect your electronics, they are there to prevent your stuff catching fire when it does fail.
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Old 26th June 2010, 04:58 AM   #6
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"The 3 dollar semiconductor will always blow to protect the 30 cent fuse."
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