Even though my first response about the capacitors hasn't made it
to phys-l yet, here's an update. It turns out the capacitor in my
office has been damaged somehow (one terminal is wobbly--something
must have been dropped on it). I went in search of some more of them,
and I found two more--one with its terminals shorted and one with no
shorting bar across its terminals. (One of them was being used as a
doorstop--they're pretty heavy.) I brought them back to my office and
checked the voltage with an old Keithley electrometer. I disconnected
the shorting cable from the shorted one and then measured the voltage
between the terminals of both. Here's what I got:
Unit Voltage
initially 0.00 V
shorted
initially 0.01 V
open
So there is a tiny but nonzero voltage between the terminals of the
unit that has been sitting for who knows how long without a shorting
cable. I'll keep checking the one that I just disconnected.
Incidentally, these are oil-filled capacitors, not electrolytic.