Where cause is unknown I closely inspect fuses to gauge whether
mechanical/aging or thermal failure and then an idea of rupture current.
This ELU 20mm 500mA F fuse had no trace of the wire , no smoke stain or
hazing at all in the glass tube. I cracked the glass expecting to see
remnants of wires or powder or something in the ends but nothing, all
"evaporated". Looks like the construction is "festoon bulb" ie totally
glass , sealed envelope with metal end caps added, something to do with it?
, I've not ground-off or heated off the end caps yet.

On Tue, 28 Sep 2010 08:39:00 +0100, N_Cook wrote:
Where cause is unknown I closely inspect fuses to gauge whether
mechanical/aging or thermal failure and then an idea of rupture current.

Remove the caps, smash it, grind it to dust, and then analyze it in a mass
spectrometer.

Or perhaps put a meter on it, and/or just replace it?

On Sep 28, 12:39*am, "N_Cook" wrote:
Where cause is unknown I closely inspect fuses to gauge whether
mechanical/aging or thermal failure and then an idea of rupture current.
This ELU 20mm 500mA F fuse had no trace of the wire , no smoke stain or
hazing at all in the glass tube. I cracked the glass expecting to see
remnants of wires or powder or something in the ends but nothing, all
"evaporated". *Looks like the construction is "festoon bulb" ie totally
glass , sealed envelope with metal end caps added, something to do with it?
, I've not ground-off or heated off the end caps yet.

I do that too, but it very much depends on the application voltage and
available current. Mains fuses can nicely metalize the glass under
high fault currents, whereas a similar current at 12V will simply melt
the fuse wire. 500mA is a fairly hefty fuse and the wire should be
visible or it should have left some indicators.

Neil S.

Ground an end face off, the way the solder dishes on closing and being shiny
makes it look like glass, normal open ended glass tube.

Owner had a pack of 10 of these fuses , probably 20 years old. 1 used and
soon failed and 2 of the remaining seven were broken cold-wire fashion, ie
straight. Looks like they were made with no give and fail just from old age.
Where the first filament went to, is still a mystery, my guess is some sort
of weird metallurgy, converting to a vapour. No problem at all with the
"failed" kit , taking less than 50mA in use

On Tue, 28 Sep 2010 08:39:00 +0100, "N_Cook" wrote:

Where cause is unknown I closely inspect fuses to gauge whether
mechanical/aging or thermal failure and then an idea of rupture current.
This ELU 20mm 500mA F fuse had no trace of the wire , no smoke stain or
hazing at all in the glass tube. I cracked the glass expecting to see
remnants of wires or powder or something in the ends but nothing, all
"evaporated". Looks like the construction is "festoon bulb" ie totally
glass , sealed envelope with metal end caps added, something to do with it?
, I've not ground-off or heated off the end caps yet.



If the fuse came out of a new box maybe it was made faulty?

--
Boris

On Sep 28, 12:39*am, "N_Cook" wrote:
Where cause is unknown I closely inspect fuses to gauge whether
mechanical/aging or thermal failure and then an idea of rupture current.
This ELU 20mm 500mA F fuse had no trace of the wire , no smoke stain or
hazing at all in the glass tube. I cracked the glass expecting to see
remnants of wires or powder or something in the ends but nothing...

If the fuse wire was tin, it may have evaporated and then oxidized.
Tin oxide is transparent.

whit3rd wrote:
On Sep 28, 12:39?am, "N_Cook" wrote:
Where cause is unknown I closely inspect fuses to gauge whether
mechanical/aging or thermal failure and then an idea of rupture current.
This ELU 20mm 500mA F fuse had no trace of the wire , no smoke stain or
hazing at all in the glass tube. I cracked the glass expecting to see
remnants of wires or powder or something in the ends but nothing...

If the fuse wire was tin, it may have evaporated and then oxidized.
Tin oxide is transparent.

Interesting. Has tin been used in fuses? I toured a company that makes
fuses for utility companies and they only use silver wire. I asked why and
the answer was nothing else is as reliable or ages like silver.

I've been fascinated by cheapo fuses that on the box claim to be
"electronically tested", whatever that means for a fuse that was probably
made by school children.

On Mon, 4 Oct 2010 22:19:39 +0000 (UTC), Cydrome Leader
wrote:


I've been fascinated by cheapo fuses that on the box claim to be
"electronically tested", whatever that means for a fuse ...

It means that they put an ohms meter or continuity tester on it and it
read shorted.

PeterD wrote in message
...
On Mon, 4 Oct 2010 22:19:39 +0000 (UTC), Cydrome Leader
wrote:


I've been fascinated by cheapo fuses that on the box claim to be
"electronically tested", whatever that means for a fuse ...

It means that they put an ohms meter or continuity tester on it and it
read shorted.

shorted?
A 10mA fuse (yes they do exist I have some in front of me)can easily measure
more than 100 ohm, pro rata for more worldly fuse ratings . Measuring of
ohmage probably gives a go/no go for rupture current.