Fuse question

Probably because a large part of the world uses a supply voltage in the region of 250v!

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If you have a 120v mains supply and the fuse is on the AC side of the rectifier then yes, that should be fine.

yes a lot of people don't get Voltage rating on fuses

e.g. It would be pointless to put a 125 Volt fuse in a 3KV microwave line to the magnetron as when the fuse "fused" the Voltage would jump the gap, so you would need a 3KV fuse or greater

so another words the Voltage rating is not imported until the fuse blown, then the fuse must stop the Voltage arcing the gap

But fuses only blow like that when they encounter a severe fault condition, ie the appliance presenting a short circuit to the mains supply, which vapourises the entire fuse wire. Sometimes the fuse wire will simply fail at its weakest point leaving a small gap, which must be wide enough to prevent an arc.

Dave

They may just have been through different testing and certification processes at the manufacturer.

Probably, though keep in mind that high current arcs can do jump much larger gaps than you might think, especially when mixed with a little metal vapor...

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Yes, and as someone pointed out, they may behave differently (producing different size gaps) when they blow gently under minor overload.

More on fuse ratings:

This is the good guts: From

(some minor editing included.

QUOTE VOLTAGE RATING: The voltage rating, as marked on a fuse indicates the fuse can be relied upon to safely interrupt its rated short circuit current. in a circuit where the voltage is equal to, or less than its rated voltage.

The standard voltage ratings used by fuse manufacturers for most small dimension and midget fuses are 32, 125, 250 and 600.

Fuses are sensitive to changes in current, not voltage maintaining their "status-quo" at any voltage from zero to maximum rating. It is not until the fuse wire reaches melting temperature and arcing occurs that the circuit voltage and available power influence the fuse performance and determine the safe interruption of the circuit.

To summarize, a fuse may be used at any voltage less than its voltage rating without detriment to its fusing characteristics, but may also be used at voltages higher than its certified voltage rating if the maximum power level available at the fuse under a "dead short" condition can only produce a low energy level non-destructive arc. ENDQUOTE

Note that any power source supplying the load via the fuse must not be able to sustain an arc into a short circuit via the blown fuse. As long as this criteria is observed a low voltage fuse (eg, 125V AC) can be used in a circuit supplied from 250V AC, or even more.

From page 150 of SWE-CHECK's Fuse Bible

Interrupting Rating (Breaking Capacity)

Also known as the breaking capacity or short circuit rating - is the maximum approved current which the fuse can safely interrupt at rated voltage. During a fault or short circuit condition, a fuse may receive an instantaneous overload current many times greater than its normal operating current. Safe operation requires that the fuse remain intact (No explosion or body rupture) and clear the circuit. LBC = Low Breaking Capacity HRC =High Breaking Capacity EBC = Enhanced Breaking Capacity.

"Smitty Two" bravely wrote to "All" (03 Jan 06 21:10:49) --- on the heady topic of "Re: Fuse question"

ST> From: Smitty Two ST> Xref: core-easynews sci.electronics.repair:353870

ST> Using "suppose" numbers, are you saying that a fuse manufacturer can ST> actually make a 250 volt fuse that will burn a 1/4" length of filament ST> and a 125 volt fuse that will burn a 1/8" length of filament? Reliably ST> and repeatedly?

ST> If we're talking about standard 1/4" x 1 1/4" or 5 mm x 20 mm fuses, I ST> say there's no damn difference between a 250 and a 125 with the ST> exception of the lettering on the cap.

ST> Now, if anyone can give me real information to the contrary, I'll ST> happily concede, but so far I haven't seen anything that I'd consider ST> more than speculation.

Perhaps a 125 volt fuse is made with the same wire as the 250 volt fuse. However the 250 has been approved at 250 and the 125 passed the

125 testing. So if there is an economy in making a 125 rated fuse over a 250 rated one then I wouldn't risk using a 125 fuse in a 250 spec'd circuit. (if made from the same spool of wire, we don't know for sure) However, the wire may not be the only story. Remember that the package is part of the fuse. Thus perhaps the thickness of the glass tube also is a function of the safety rating for the 250 and 125 spec too. Recall there is 4 times more energy involved between 125 and 250!

A*s*i*m*o*v

... Thomas Edison invented the "Light Emitting Resistor"

Read Ross Herbert's post, that's all I need to say on the subject. Perhaps next time you might keep it civil rather than jumping on people and making a dick of yourself.

Dave

I did read the post as being rather hostile TBH. However, I withdraw my comments and offer my apologies, you say there was no intended hostility and I accept that.

No hard feelings I hope!

Dave

Maybe the confusion here is that the OP was talking about AC fuses. DC is a whole different story esp. in free air. The physics lab where I worked for a while had a 100 VDC supply 100 amps available. I was designing a reversing switch for an inductive load and drew an arc that completely ate the relay in the test cell. Turned it into a puddle of molten metal and plastic, walked out the power leads and snapped off. Talking to engineers at the local transit system they were very familiar with this. "We just walk away". Richard