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interesting secondary phenomonea
Original poster: "resonance" <resonance@xxxxxxxxxxxx>
It's because the charge is not residing in the metal wire which is
connected to ground --- the charge is residing in the dielectric
(wire coating) between the grounded wires.
A coil does have a DC component which can momemtarily charge the
dielectric, ie, plastic or enamel wire covering. The def of a cap is
two plates separated by a dielectric.
Recall the old physics trick of the removable dielectric Leyden
jar? A Leyden jar type cap is charged, and, then, while charged,
with a plastic stick, the center conductor is carefully removed and
the outer conductor is removed. They are shorted together, and also
both shorted to a ground.
The cap is then reassembled and the cap is powerfully
discharged!! It proves the dielectric stores the charge, not the
plates. In a Tesla coil, under certain conditions, the plastic PVC
coating on the wire, or enamel coating, or protective coating over
the windings, will hold a DC charge that discharges to you when you
touch the sec coil. Good idea to at least slowly run the back of
your hand or a ground along the sec winding to discharge any of this
"static electricity" that remains.
Many coils usually don't have this problem some but coils with a
heavy coating or PVC insulated wire coils can exhibit this phenomonea
under certain conditions. Caution is in order until you discover if
your particular coil design exhibits this interesting process.
The atomic electron orbitals are stretched when the cap is charged,
and as they return to their normal obits, they give up some electric
charge to the plates again.
I've noted it also seems to be more prominent in coils that are
suddenly shut off at high power as opposed to operation in which the
variac is slowly diminished. Perhaps a gradual shutdown of your
particular coil will prevent this event from occuring. You could do
some experiments with a grounded wire in a very dark room and you may
see some "St. Elmo's fire" as you drag the wire down the side of the
I've gotten bit by a couple secondaries in the past, which I thought was
rather odd since they were still connected to ground at the time. I'm
thinking that perhaps it's an electrostatic charge built up on the enameled
outside of the secondary that carries the "bite". (?) Now, before I decide to
touch a secondary that's just been running, I take a grounded wire and go
over the outside of it a bit. (I bend the end over so I'm not scraping the
finish off) Seems to have done the trick for me.