On 2012-09-26, Jon Elson wrote:
Michael A. Terrell wrote:



The winding may have opened & arced, causing plasma which ignited the
oil. I used to see hundreds of bad clock motors a year, when one shop
did school clocks & fire alarms. Most had bad gears, but some had open
coils and burn marks.

Yup, I agree. An impedance-limited motor can't get hot enough to
ignite oil. But, if there was internal or external arcing, that could do
it. I'm still a little surprised internal arcing could do it, as these
motors are usually pretty well closed up. Either it arced internally
for quite a while, or until an outside wire burned off and dropped into
the usual oily mess on such pumps.

That last is rather likely. The wires from the motor were
something like 26 ga or 28 ga -- connected to 16 ga to go back into the
rack of electronics.

It really seems a properly-sized
fuse should have cut this off before it got to that stage. Might be
something to install while rebuilding.

I had a fuse in there -- but it certainly was not
properly-sized. It was the fuse in the component fuse holder from a
terminal block stack from the old machine. It turns out to have been
rated at 5A (still normally reasonable -- and I don't remember ever
seeing an electric clock with a fuse built in. :-)

But the fuse which was in there was quite visibly blown. (3AG
size, FWIW.)

Maybe a 1/2 A fuse would have been adequate and easier to find.
a 1/10 A would be even more reasonable.

I did a web search for a link between BiJur oilers and fires,
and found nothing. By now, you can probably find this thread, the way
the net works. :-)

Thanks,
DoN.

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