Fuse failures

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Hv&Lv

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Did it cause any damage to the downstream equipments?

If no,I think the rupturing capacity of the fuse might have been exceeded so that even though the fuse failed catastrophically,it nevertheless caused no damage to the downstream equipments it protected.Correct?

It didn't cause damage to any equipment, and as far as the cartridges, they get old and after blowing quite a few times, the boric acid lining wears out and the cartridge starts to deteriorate. After all, it gets hot in there extinguishing the arc. The fuse is designed to fail catastrophically, we just replace it and throw it in again.

I have seen things like voltage regulators on generators burnt out or some PLC boards burnt out after trying a fuse and it blows.
 
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T.M.Haja Sahib

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The fuse is designed to fail catastrophically.

Please furnish more details,if possible.Because during the catastrophic failure of above fuse installed in the open air,it may throw the broken pieces of its (ceramic) cartridge all around and any person nearby is liable to be injured.

I have seen things like voltage regulators on generators burnt out or some PLC boards burnt out after trying a fuse and it blows.

Was the fuse also suffered extensive damage?Thanks.
 

Hv&Lv

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The fuse is designed to fail catastrophically.

Please furnish more details,if possible.Because during the catastrophic failure of above fuse installed in the open air,it may throw the broken pieces of its (ceramic) cartridge all around and any person nearby is liable to be injured.



Was the fuse also suffered extensive damage?Thanks.

The tubes aren't ceramic, they are resin. Look up expulsion fuses, I am sure there are some of them on top of the poles there also. The fuse links are made there also.
 

Hv&Lv

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Anyway,catastrophic failure should not be allowed for in any design.

Perhaps you and I have a different definition of catastrophe. " a failure... a disastrious end..." The fuse blows and is destroyed, unable to ever be used again.
 
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T.M.Haja Sahib

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Perhaps you and I have a different definition of catastrophe. " a failure... a disastrious end..." The fuse blows and is destroyed, unable to ever be used again.
By catastrophic failure,I mean not only the fuse element but also the fuse cartridge is shattered by the fault the subject fuse tried to clear.In the case of expulsion fuse,only the fuse element normally goes,when the fuse operates so that it may be reused by replacing the fuse element with a new one.
 

iwire

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By catastrophic failure,I mean not only the fuse element but also the fuse cartridge is shattered by the fault the subject fuse tried to clear.In the case of expulsion fuse,only the fuse element normally goes,when the fuse operates so that it may be reused by replacing the fuse element with a new one.

As there are many types of fuses and applications for fuses perhaps a link or picture of the fuse you have in mind would be a help to the rest of us.
 
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T.M.Haja Sahib

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As there are many types of fuses and applications for fuses perhaps a link or picture of the fuse you have in mind would be a help to the rest of us.
This thread is about fuse failures in general.So do you want a picture of expulsion fuse as mentioned in post#46?
 

iwire

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This thread is about fuse failures in general.So do you want a picture of expulsion fuse as mentioned in post#46?

You can't really apply too many general statements to all fuses.

Most fuses that I deal with are contained in an enclosure so that regardless of the mode of failure they are safe.

On the other hand I think Hv&Lv is talking about pole top fuses which are not enclosed but are so high from people that they do no harm when they fail.

In my personal opinion you cannot talk about fuses mode of failure and it's consequences without confining the conversation to certain types of fuses. However it is your thread so you can do whatever you want.
 
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ptonsparky

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The failure of a pole top fuse is about the last on my list of worries to cause me injury. Although I have seen the fuse holders laying near the pole after they operate. Hard Hat area, flash protection, hearing? The center of my North 40 is looking better all the time, but then there are the dang badger holes.
 
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T.M.Haja Sahib

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Most fuses that I deal with are contained in an enclosure so that regardless of the mode of failure they are safe.

It is not so much about the safety of people near any malfunctioning fuse as about the safety of the circuit and the devices the fuse is supposed to protect.

you cannot talk about fuses mode of failure and it's consequences without confining the conversation to certain types of fuses.

Those certain types of fuses are...............
 
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T.M.Haja Sahib

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Rewirable fuse

Rewirable fuse

In case of rewirable fuse with porcelain fuse base,repeated fuse blowing on fault over time deposits a conductive layer on the inside of fuse carrier which may result in fuse failure.To avoid this the fuse wire was enclosed in an asbestos tube in fuse of earlier times..............
 

Hv&Lv

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I have had a couple of the old renewable Shawmut 200 amp cartridges blow in half (or out) but it didn't damage anything downstream.( unless you count the bad motor blown out!) I haven't found too many places that stock the renewable fuses though.. Maybe I have been looking in the wrong places...
 
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T.M.Haja Sahib

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As I said I really wish you would tell us what type of fuse you have in mind.

If V-I characteristic is plotted for a circuit resistance,it is a straight line. The V-I characteristic of the arc of a fuse when it is interrupting a fault resembles a parabola.The combined V-I characteristic of circuit resistance and the arc again resembles a parabola.The voltage of the circuit is represented as a horizontal straight line.The arc of fuse could operate stably at one of the intersection points of the parabola and the horizontal line causing the fuse failure.So the combined V-I characteristic should lie above the horizontal line of circuit voltage so that there is no common points between them.Otherwise it might cause fuse failure during a fault clearance by the subject fuse.
 

Besoeker

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If V-I characteristic is plotted for a circuit resistance,it is a straight line.
This isn't true in general. You mention rewirable fuses with porcelain bases.
I've come across those in the past and the fusible element was (tinned) copper wire.
This has a positive temperature coefficient.
We, as a manufacturer, typically use this characteristic to determine winding temperature rise in a motor or transformer winding after a heat run.
Measure the winding resistance and ambient at the start and then again at the end and you can calculate the winding temperature rise from the change in resistance.

With a Cu element, the more current it takes, the hotter it will get and the higher the resistance will be. It isn't a straight line VI characteristic.
The melting point for copper is a bit over 1,000?C.
When you get to that point, which you must at least if the fuse is to rupture, the resistance will be several times that at ambient.
 
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T.M.Haja Sahib

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With a Cu element, the more current it takes, the hotter it will get and the higher the resistance will be. It isn't a straight line VI characteristic.
The melting point for copper is a bit over 1,000?C.
When you get to that point, which you must at least if the fuse is to rupture, the resistance will be several times that at ambient.
It is series circuit resistance i.e the resistance of wires etc and not that of fuse in operation is considered here,which may be assumed to have linear characteristic.
 

Besoeker

Senior Member
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It is series circuit resistance i.e the resistance of wires etc and not that of fuse in operation is considered here,which may be assumed to have linear characteristic.
For the VI characteristic to be linear, the resistance would have to be constant.
Do you not agree that it changes with temperature?
And that the change is appreciable during the pre-arcing period as the element ruptures?
 
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