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Jon Elson[_3_]

wrote:

So my next best guess was that perhaps it is a 40 volt unit and with a
center tap to case ground. So half expecting to see 80 volts across the
secondary I read 0 volts. However I did confirm the rating on the label.
It was a 24 volt non tapped transformer and an ohm meter check between
each secondary terminal and ground showed infinity. And interestingly the
same check across the two secondary terminals showed 1 ohm.
VERY strange. My guess is there was a failure of the primary that
shorted a spot on the primary to the secondary. (This should NEVER
happen!) The primary was open, the secondary was being energized
from a spot on the primary where there was a lot of inductance, therefore
it didn't go all the way to 120 V. That would explain all the readings
you got, but this sort of short should NOT be possible. You may find
a non-infinite resistance reading between one of the primary wires
and the secondary.

It is also possible that there was enough capacitance between primary
and secondary to give the 40 V reading without an actual short.

Jon