Re: TC discharge... safe or not

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

Tesla list wrote:

 > Original poster: "c d by way of Terry Fritz <twftesla-at-qwest-dot-net>" 
<vbprg1-at-hotmail-dot-com>
 >
 > When people refer to the skin effect they are refering to the tendancy of
 > high voltage to travel along the outer surface of a wire or channel instead
 > of the interior of the wire. Ok Im not a scientist and I have actually only
 > recently learned about all of this, but I am truely amazed at how many
 > "smart people" take this literally in a human biology sense. The skin of
 > your body is NOT being refered to.
 >...

Not exactly, but close. It's high-frequency current that tends to travel
close to the outer (nonconductive) surfaces of conductors. And this
really means the outer surface of any conductor surrounded by a less
conductive medium. Static charges tend to move to the outer surface of
conductors, but this effect is secondary, because these charges are
charges that accumulate in the conductors, not charges flowing through
them.
A calculation of the skin depth at usual Tesla coil frequency and
usual resistivities of the human body leads to a good fraction of a
meter, so effectively there is no skin effect. The currents just
travel through the smaller impedances found (blood, nerves), breaking
away any insulation in the path (skin, joints, etc.).
High-frequency currents are not felt because the nervous system doesn't
respond to them (remember that you can't hear frequencies above 20 kHz.
By a similar mechanism, you can't feel electricity above 20 kHz).
If no serious damage occurs, it's because the current is not high
enough to heat the tissues sufficiently.
Note also that Tesla coil discharges to ground are not much different
from dc discharges, as from a Van de Graaff generator. The main
difference is that instead of a few discharges per second a Tesla
coil produces hundreds of discharges. There are other differences
too, as a tailing current after the main discharge, that may include
some oscillations. If the energy of each discharge is greater than
about one Joule, some damage may occur. If greater than 10 Joules,
the risk is very large.

Antonio Carlos M. de Queiroz