Replacing ahigh voltage fuse

[93lt1]

I agree completely!!

There is some dangerous mis-understanding of how fuses work and what the ratings mean going on here. Just because you have a mathematically correct solution, it doesn't mean that the answer correctly represents the physical reality!

I know that a fuse melts because of I-squared-R heating. It is the CURRENT that causes the heating, regardless of the voltage applied. That is why you can use a 120 VAC rated fuse on a 24 VDC circuit.

saifullah99319's theory of measuring fuse protection in watts goes against everything I have ever learned about fuses.

 

[rogerhollingsworth]

Fuse air gap

DICKDV and Tom have given you the same advice, as I will.
Voltage rating is to ensure the remaining air gap between the two ends of the blown fuse is great enough to extinguish the arc. Ohms law don’t really cover fuses.
Use the proper fuse, put some in stock while you are at it.
It is better that someone take a hit for not having the correct fuse in stock rather than taking a hit for a fire due to using the WRONG fuse.
Don't forget, all the engineering for that fuse application has been done, no need to do it again.

Never sacrifice accuracy for speed.
Roger

 

[stevez]

I think when having to choose your fuses for this application you should get expert advice.Go to http://www.ferrazshawmut.com/resources/sel_app_sw.html

 

[PLucas]

I think when having to choose your fuses for this application you should get expert advice.

I am not sure 'expert' advice is needed here, his question was answered by DickDV and by Tom.

Simply, do not even think about replacing a 5kV 0.75A rated fuse with a 600v 0.75A rated fuse, if you cannot find the exact one (5kV) then up the rated voltage, but keep the current rating the same! So a 10kV 0.75A fuse can be used to replace a 5kV rated one.

There was a couple of nonsense replies (as Steve Etter pointed out) to this post that should be totally disregarded!

paul

 

[stevez]

There was a couple of nonsense replies (as Steve Etter pointed out) to this post that should be totally disregarded

!

Paul ,that is the point.You are able to decide that there are nonsense replies.Not everybody is so fortunate.
If one takes the advice of the experts (such as a fuse manufacturer) I think that it is a lot safer.

Steve

 

[Steve Etter]

Actually, Stevez makes a very good point, especially with regard to this particular thread.

Had locus asked for direction on how to go about sizing a particular fuse, most of us would have directed him to one industry resource or another and posibly given some rule of thumb techniques for checking himself. But that is not what happened.

Instead he asked specifically if a certain fuse could be used in place of his dead one. To that end, I believe the common (and correct) answer was "No", but there was, even then, confusion and misdirection thrown into the mix.

We all kinda took a tangent to try to help identify the proper size and what else might be acceptible and I think now would be the right time to answer the question the way we probably should have in the first place (and actually the way Tom and Stevez already did).

Tom wrote: "If you aren't sure about swapping the fuse with a different one, DON'T DO IT!!!!!!"
Absolutely right. If you don't know, stick with the original.

Stevez wrote: "Take the advice of the experts (such as a fuse manufacturer) I think that it is a lot safer."
Once again, absolutely right. In the end, you (locus, in this case) are ultimately responsible for this. None of us here are.

Whatever you do, make sure YOU understand it before you do it.

Steve

 

[rogerhollingsworth]

QUOTE]I think when having to choose your fuses for this application you should get expert advice.[/QUOTE]

Having the original fuse with the equipment, what more expert advice do you need? OEM should be good enough, I don't think they flipped a coin to select the fuse.

Roger

 

[LadderLogic]

... c.now you decide to connect 600v-.75amp rating fuse.
that means this fuse can't pass over 600*.75=450watts
in your circuits...

Weeeeellll. Here is saifullah's mistake.

When the fuse is OK and 0.75 Amp current is flowing through it - the voltage across the fuse is NOT 600 Volt, it is, for all intents and purposes, is zero. Nil. Nought.
On the contrary, when the fuse is blown, there is 600V aross it - but the current is, unfortunately, zero. Nil. Nought...

Locus, I should join everyone else pleading: disregard saifulla's analysis, please! He made a grave mistake by applying Ohm's Law to a wrong part of the circuit!

 

[ed]

Locus:
Here's what I would do if I was faced with this problem. I would get the exact replacement or it's equivilent. There's more to fuses today than just amps and volts. This is not a typical fuse you'd find at local jobber's warehouse. It was specified for this particular application. Contact the manufacturer of the machine or industrial electrical supplier and get the EXACT replacement.

 

[93lt1]

I agree...

Weeeeellll. Here is saifullah's mistake.

When the fuse is OK and 0.75 Amp current is flowing through it - the voltage across the fuse is NOT 600 Volt, it is, for all intents and purposes, is zero. Nil. Nought.
On the contrary, when the fuse is blown, there is 600V aross it - but the current is, unfortunately, zero. Nil. Nought..

He made a grave mistake by applying Ohm's Law to a wrong part of the circuit!

Ohm's law applies to every part of the circuit.

You are applying Ohm's law to the circuit correctly!!

0V at .75A = 0 watts
600V at 0A = 0 watts

Of course this would be only in a perfect world...everything has resistance and there would be a little voltage drop across the fuse, but your theory is correct.