.......fake fuses query......

[JohnW2]

In some counterfeit/copy fuses no eyelet is used in the internal construction and the wire often can be seen to be
trapped against the side wall of the tube under the cap causing a bulge. ... Where an eyelet is used to attach the fuse element to the end cap it is much deeper than eyelets used by approved...

What are these "eyelets"? As I said, in the (hopefully not fake) ones I looked at, the fuse wire appeared to be simply connected (by welding/brazing/soldering/whatever) to a little 'pimple' protruding from the middle of the inside of the end of the cap - I saw nothing I would describe as an 'eyelet' (unless it's this 'pimple').

I've also been pondering how on earth they manufacture these things - in particular how they manage to attach the 'second' end of the fuse wire (unless it's soldered - which the list you posted says it's not) - any ideas?

In any event, I'm not sure what in that list of features of fakes you've just posted explains "In a genuine fuse the fuse wire is connected to the end caps in a way that reduces the amount of heat that can reach the end caps from the fuse wire" - is that in some way related to thee alleged 'eyelets?

Kind Regards, John

 

[bernardgreen]

I've also been pondering how on earth they manufacture these things - in particular how they manage to attach the 'second' end of the fuse wire (unless it's soldered - which the list you posted says it's not) - any ideas?

I did once know the answer but those notes have long gone ( like some of my memory ). So I donated a fuse to science and dissected it.

The tube, rings and fuse wire are assembled and then the end caps are pressed onto the ends. I recall they were put on hot so that they gripped tightly when cool and contracted.

The metal rings may be slightly cone shaped to be flattened by the caps thus ensuring good contact between ring and cap.

Sand not shown for clarity

 

[bernardgreen]

Forget rings....... change it to eyelets.....

 

[ban-all-sheds]

In a genuine fuse the fuse wire is connected to the end caps in a way that reduces the amount of heat that can reach the end caps from the fuse wire. In many fakes the wire is in direct contact with the caps and the caps heat as the wire heats.

No solder is used in the end contact of the approved fuses.

They're probably all gone now, but if I ever find one of the fuses my Dad repaired by soldering fuse wire between the end caps on the outside of the body I'll post a photo.

 

[bernardgreen]

Genuine fuses probably do not use copper as the fuse wire.

Copper melts at aboit 1000°C so the fuse could become very hot before the wire melted..

Genuine fuses probably use a metal with a very low melting point, for example Woods metal which melts at 70°C

 

[DetlefSchmitz]

Genuine fuses probably do not use copper as the fuse wire.

Copper melts at aboit 1000°C so the fuse could become very hot before the wire melted..

Genuine fuses probably use a metal with a very low melting point, for example Woods metal which melts at 70°C

Seriously? It is my understanding that copper is the usual metal. Indeed BS7671 even used to have a table of the copper wire diameter required for various current ratings. This used to be reproduced in the Farnell catalogue next to the BTC selection.
Wood's Metal?... I don't think so.

 

[bernardgreen]

Yes seriously

https://circuitglobe.com/fuse-wire-materials.html

Fuses on which the wire can be replaced are more capable of surviving a bit of copper wire glowing red hot.

 

[ban-all-sheds]

"Silver is used as a fuse element because it has the following advantages

• It does not get oxidized, and its oxide is unstable.

.
.
"

 

[DetlefSchmitz]

Interestingly, BS1362 doesn't seem to limit temperature rise. It says this is a matter for the fuse holder. The more I look at it the more I wonder...

 

[ban-all-sheds]

Genuine fuses probably use a metal with a very low melting point, for example Woods metal which melts at 70°C

Wouldn't that be problematic given that conductors and terminals etc may reach 70°C in normal operation?

 

[bernardgreen]

Wouldn't that be problematic given that conductors and terminals etc may reach 70°C in normal operation?

for example Woods metal which melts at 70°C

Another alloy with a higher melting point would be used for installations where 70°C could be achieved normal use.

I believe the standard 13 amp plug is not rated to operate normally at 70°C so Woods metal may be appropriate for fuses in plugs.

The alloy chosen should melt at a temperature lower than the temperature at which the fuse holder starts to degrade.

 

[rsgaz]

I believe the standard 13 amp plug is not rated to operate normally at 70°C

BS1363-1 can be a bit vague at times(like all standards, sadly), such as...

"16.1 Plugs and their surroundings shall not attain excessive temperatures in normal use." (no definition of "excessive", of course)



...but then again, a temperature rise of 52 degrees above ambient is permitted, for the "Accessible external surface". (See table 4)...

So 70° is clearly acceptable; the 'internals' must be even hotter! (there would be loud swearing from me if I touched one that hot!!)

 

[ban-all-sheds]

I believe the standard 13 amp plug is not rated to operate normally at 70°C so Woods metal may be appropriate for fuses in plugs.

Those same fuses are also for use in FCUs.

 

[bernardgreen]

Those same fuses are also for use in FCUs.

And the point of that statement of obvious fact is........ ?

 

[ban-all-sheds]

That "I believe the standard 13 amp plug is not rated to operate normally at 70°C" is of no relevance, because we know that when used in an FCU the conductors, and therefore the fuse holder, and therefore the fuse end caps, and therefore (at least some of) the fuse wire may legitimately reach 70°C.