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. 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.

Jon