UL & fuse rating

maybe with 600V fuses.. that would be the next step up.

--
http://webpages.charter.net/jamie_5"

** I think you are worrying about nothing.

That 250 volt figure on the fuse is a *nominal* rating - not some maximum breaking voltage never to be exceeded.

The fuse link will easily work as intended at 277 VAC or more.

Your 277 VAC figure is the upper limit of a nominal 240 VAC system and indicates the PSU will still function with safety and within specs at that input voltage.

BTW:

You sure a fast acting fuse is OK here ?

What about the inrush surge ?

...... Phil

Your label ratings are the problem - they should reflect AC nominal line voltages only (1e 110-240). UL testing automatically adds and subtracts margins for evaluation to reflect typical line voltage tolerances in the field. If you intend to list operation over the wider range on your product label, it will be evaluated to those voltages plus and minus similar margins.

This means it will be evaluated for continuous operation and single fault abnormals over a 76 to 318VAC range, to carry the extended range markings, something that you must take into account. This may place your equipment outside the operating voltage class that you intend it for.

The fact that your device operates over the range indicated earlier can be added to your specification, for custmer/client reasurance, but the label should only reflect the nominal environment, as a wider range is required simply to claim normal function.

RL

Wow talk about coincidence! I've just finished research and writing a page all about fuses for the club website (will be uploaded on Sunday)

Here is an excerpt from webpage about the voltage rating:

Voltage rating. The voltage rating has no effect on the current rating but is important. When a fuse blows an arc is developed between the two ends of the broken fuse element and if the voltage across these ends is high enough, the arc will be maintained and the current will not be interrupted. This condition could result in considerable damage to the equipment, even melting of the fuse body and / or fire. Arcs are readily produced in high voltage circuits or where inductive loads are being used and in these conditions the voltage rating of a fuse must not be exceeded.

Fuses can be used for their current rating at all voltages (AC and DC, there is no real difference where a fuse is concerned) up to their maximum voltage. When it is known for certain that although the circuit has a high voltage present the power available is limited, it is possible to use a fuse at a higher voltage than that for which it is rated. This is common practice in domestic electronic equipment and quite safe. However, if you have any doubt, keep within the voltage ratings given by the manufacturers.

Read the whole page from Sunday on:

Highfields Amateur Radio Club Website:

It will be in Constructors Corner, full URL for that page will be:

But don't forget it won't be there until Sunday! HTH

Brian MW0GKX

.

The voltage rating of the fuse does not indicate the operational voltage of the fuse. The voltage rating determines the maximum voltage that will not jump the gap between the elements after the fuse has already blown. So the fuse will operate at the rated voltage and any voltage below the rating.

Not true. DC is a more severe condition. AC cycles through zero regularly allowing an arc to extinguish itself. There is no such condition for DC so a DC rated fuse has to resist sustaining an arc in conditions that AC fuse should never see. You should not use an AC rated fuse in a DC circuit.

Robert

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Posted via a free Usenet account from http://www.teranews.com

Thanks Robert. I'll do more research in that area before I post the finished article.

Unfortunately I have to rely on my sources which, as you see, are not always accurate!

Brian

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here

text -

".. The voltage rating of a fuse is NOT an indication of the voltage the fuse is designed to withstand while carrying current. The voltage rating indicates the ability of the fuse to quickly extinguish the arc after the fuse element melts and the maximum voltage the open fuse will block. In other words, once the fuse has opened, any voltage less than the voltage rating of the fuse will not be able to "jump" the gap of the fuse. Because of the way the voltage rating is used, it is a maximum rms voltage value. You must always select a fuse with a voltage rating equal to or higher than the voltage in the circuit you wish to protect. .."

Your reply indicates that a fuse would arc with AC, but then clear it self with the changing cycle ~ The fuse should never arc at all....

MIL-PRF-23419: Fuse selection: The following steps should apply in the selection of a fuse for any application: Step 1: Select a fuse with a voltage rating equal to or in excess of the circuit voltage.

Thanks for that, I also (now) have a tech doc that explains the why between and AC and DC so I'm rewriting that section.

Thanks again for the head up on that. (Note to self, when you've researched all you can, do some more!)

Brian

shed

ways

text -

Hmm? Does that indicate an issue only above 600V? I'm a digital engineer not a power line guy.....

See for example Pg 185 of

The AC/DC differential tends to be glossed over a lot (that reference will tell you it's important but not why). One way this shows up as physical difference in AGC style fuses is that DC rated fuses are often ceramic rather than glass, presumably to contain the arc.

Robert

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Posted via a free Usenet account from http://www.teranews.com

look at fuses rupture current rating - it is very, very different for DC c.f. AC.

it might be worth talking about rupture current ratings too - the current which a fuse can successfully interrupt without blowing itself to pieces (I'm paraphrasing).

If you have ever seen the shattered remnants of a glass fuse - or better still, *not* been able to find the remnants of a glass fuse - then you have seen what happens when the supply fault current is > the fuse rupture current.

Cheers Terry

"Robert Adsett"

** Correct.

** Nonsense.

Everything depends on the available current under fault conditions. Standard glass fuses are not able to break large AC currents at their rated voltages - for that job you need a HRC ( high rupture current ) type. Such fuses typically have ceramic bodies and are filled with sand and/or use multiple strands of fuse wire.

With DC circuits, the voltage and available current level under fault

*together* determine the type of fuse needed. DC voltages under 24 volts usually present little problem for standard glass fuses and they also have no trouble breaking up to 500 volts DC, if the available fault current is only a few amps.

Where a supply of high DC volts and amps must be fuse protected, the usual solution is to fuse the nearest part of the AC circuit that supplies the DC one.

...... Phil

there

There will be an arc. It just won't be sustained. The fuse link won't just disappear it will open from some starting point so there will be a gap a few atoms thick and the current will be carried across the gap on an arc. How long that arc is maintained depends on a number of factors including the interrupted current and voltage. The fact these will go to zero on an AC line allows an arc to extinguish that would not on a DC line.

Robert

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Posted via a free Usenet account from http://www.teranews.com

finished

always

No, in fact the fuses I refered to are 250V fuses. Some of the glass fuses if IIRC are rated for 250VAC/32VDC. Most only have the 250VAC rating. The fuses rated for 250AC/250DC are in ceramic cases. I know this because I routinely need 60VDC rated fuses, 32VDC is easy to find

60VDC is less common. I've never seen a fuse specified with enough information to qualify an AC rated fuse in a DC circuit, typically all you get is voltage and interrupt rating.

I have a reference somewhere (I think it was Littelfuse) to a presentation of design of automotive blade fuses for the proposed 42V automotive bus. One of the photos was of the remains of a standard automotive blade fuse after testing.

Robert

--
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"Robert Adsett"

** Virtually all spec sheets give the maximum * breaking capacity * of a fuse.

The designer has to know ( or determine by test) what magnitude of fault current that needs to be broken in each application.

Only rarely does the huge current from a dead short condition need to be catered for - cos there is always another fuse or circuit breaker in the AC supply wiring.

** Standard ( ie 32 volt DC rated ) blade fuses have a quoted breaking capacity of 1000 amps.

...... Phil

I do believe that's what I said.

Yep

That does make the rather large assumption that there is an AC circuit feeding the DC. In a lot of the stuff I do the DC bus is not fed directly from an AC bus.

But that provides no guidline to their performance on a 60V bus. That's the point I'm making. The AC ratings provide no guide to acceptable DC use and the DC ratings do not provide any guide to use at higher than rated voltage.

Robert

** Posted from **

"Robert Adsett" Terry Given

** You two vile, autistic PIGS should go f*ck each other.

Make lotsa brain dead, stubborn piglets.

Oink, oink oink ...

.... Phil

Try looking for 600 V fuses if you want a UL rating (I do not know of glass being available at 600 V and up). The 250 V volt fuse would disqualify you automatically.

Not at all Phil. 277 V is the line to neutral voltage for 480 V

3-phase 4-wire services.