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Bud--

wrote:
On Sat, 20 Nov 2010 08:50:26 -0800, Smitty Two
wrote:

In article ,
wrote:

I have seen many fuses "just fail" over the last 50 years, both
automotive and "mains". And like incandescent (filament) lamps, I've
seen them "mend" themselves temporarily - sometimes several times,
before final total failure.
An intermittent "failed" fuse can really be a bugger when
troubleshooting an intermittent electrical problem.
Failed fuses don't mend themselves. However, a common automotive failure
is intermittent connections behind the fusebox. Pulling and replacing a
fuse restores the connection, for a minute, day, or week.

I beg to differ. The fuses can arc weld themselves back together and
work for a while, then re-fracture. Depending on temperature changes
etc, this MAY happen more than once, but even once is a rare
occurrence. Rare, but it happens.

On most current automotive fuse boxes there are no "connections"
behind the fusebox that would be influenced by removing the fuse. -
and replacing the fuse invariably solves the problem - often for the
remaining life of the vehicle.

Same thing happens in fused distribution panels - both with plug
fuses (the round glass screw-in common fuse) and with cartridge fuses,
on occaision. Bump the fuse, or have the temperature go up a few
degrees, and the fuse makes contact again, allowing light loads to
operate. Sometimes they will "weld" themselves and not cause a problem
again for several days.
Looking at the fuse there is no sign that there is anything wrong -
but sometimes if you tap the fuse in the dark you will see a faint
blue arc inside the fuse body, and a light connected to the circuit
will either flicker off, or faintly flicker on..

Maybe it happens in Canada. Very doubtful in the US.

Fuse elements on power systems burn a gap when they open. The fuse
elements are almost always quite rigid and can't vibrate back together.
I really don't think UL would like that behavior.

In many years in the industry I have not seen a fuse "just fail". Maybe
you could buy bootleg fuses from the US.

--
bud--