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Re: simple question

Electrical ground, or more properly, a safety ground, is the "third" prong
on the plug. It's purpose is to make sure that the cases of equipment, etc.
remains at ground potential, even if there is a short inside from the power
line. In the case of such a short, typically the circuit breaker would trip
or the fuse would blow.

It's designed to work for relatively low frequencies (i.e. 50 or 60 Hz), so
the fact that it's a fairly long wire isn't a big deal. The important thing
for a safety ground is a low resistance, so that if there is a fault,
enough current will flow to cause a trip, and to insure that even if there
is a fault current, the voltage on the device being grounded is low enough.
A typical resistance would be around an ohm, so even with 20 amps flowing
in a "line to case fault", the case voltage would be only 20 volts, which
is safe.

An RF ground, on the other hand, refers to providing a suitable "ground"
for the top terminal of your TC to work against. It needs to have low
impedance at a few hundred kHz, but whether it is actually at "DC Ground
potential" isn't as important (although it should be, for safety reasons).
The ideal RF ground would be a conductive sheet extending from the bottom
of your coil for quite a distance (opinions vary on how far, but I think
that if the radius of the ground sheet is 2xcoil height, it is probably big
enough).  Wet dirt (excuse me, "soil") is a fairly good conductor, so if
you drive a decent rod into the soil and it is close to the coil, then
you've got that extended ground plane you want.  On the other hand, if that
ground rod is 50 feet away, and you've connected it with some speaker wire
you found in your little sister's stereo, it probably isn't so hot.  Why??
because that skinny wire has a lot of inductance (several uH per meter),
and at 100-200 kHz, the impedance is pretty high.

----------
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: simple question
> Date: Wednesday, December 01, 1999 1:22 AM
> 
> Original Poster: LEST2001-at-aol-dot-com 
> 
> This is such a simple question I'm embarrassed to ask, but everyone has
been 
> so helpful. What is the difference between RF ground, and an electrical 
> ground?   
> Thank you,
> Leslie
> 
>