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Ground question


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From:  Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
Sent:  Sunday, March 15, 1998 5:46 PM
To:  Tesla List
Subject:  Re: Ground question

Tesla List wrote:
> 
> ----------
> From:  ajones-at-nwga-dot-com [SMTP:ajones-at-nwga-dot-com]
> Sent:  Sunday, March 15, 1998 7:26 AM
> To:  tesla-at-pupman-dot-com
> Subject:  Ground question
> 
> Coming out of 'Lurk Mode'....
> 
> I've been pounding some ground rods to replace the wimpy ground I had
> been using and have a question about the hookup. There is a cable
> running to my satellite dish that will cross the path from the ground
> rods to the coil. Will there be a problem with this? I could
> disconnect the cables at both ends when running a coil if necessary
> but there is a hill to climb to get to the dish. I'm not exactly old
> and worn out yet, but would prefer not to do this.
> 
> What's in the wire going to ground? Is there voltage or current flow?
> I've always wondered about this and have been waiting years for
> someone else to ask. Since I don't remember if anyone has, I guess I
> have to put on the dunce cap today and grin-n-bear it  :-)
> 
> What about running the ground wire overhead and then dropping straight
> down to the ground rods? I remember someone saying two or three years
> ago that flashing or strap could be duct taped to the floor and run
> out this way. That is the reason for my question about what is
> actually in the ground wire. If this would be safe then my way would
> seem to be also. I have no problem with taping flashing or ground wire
> to the floor, but I still have to get it across the sat cable and
> going overhead seems to be the only way, short of going all the way
> around the house. And the ground wire is certainly stiff enough to
> stand up for the few feet to the ground rods.
> 
> And would the wire radiate out in the open like this? I know better
> than to hook a wire to the top of a coil since that would be an
> antenna, but what about the ground?
> 
> Okay, that's enough questions for this year. Now back to......
> 
> 'Lurk Mode'
> 
> Thanks,
> Alan
> _____________________________
> ajones-at-nwga-dot-com

Alan,

When a Tesla Coil operates, the secondary coil's inductance resonates
with the combined secondary and discharge terminal capacitance. The
other "plate" of this capacitor is the earth (and, for that matter any
other nearby conductive object). Energy was inductively coupled into the
secondary resonant circuit from the primary tank circuit when your
primary gap fires. Assuming that your gap "quenches" at the right time,
energy transferred to the secondary is prevented from transferring back
to the primary. It then alternatively transfers back and forth between
the secondary's electrostatic field (1/2 CV^2), or its electromagnetic
field (1/2 LI^2), all the while losing energy to streamers, resonator
coil and groundpath resistance, and radiation. The peak currents which
exit the base of your seconday will typically be 5-10 amps for medium
coils, and can exceed a hundred amps in a large coil. 

Now, IF you have a good grounding system (i.e., multiple groundrods and
a relatively short round wire or flat strap connected to the base of
your secondary) the voltage peaks at the base of your secondary will
only be in the 100 - 500 volt range. A poorer ground can easily cause
this to be much higher. An interesting experiment is to put a standard
120 volt tungsten light bulb in series with the groundlead at the base
of the coil - even smaller coils have no difficulty lighting the
filament from the RF current. Alternatively, a small (1/8" max) gap can
be inserted between the secondary's base lead and its ground connection
- you'll see a bright blue-white arc that looks almost like a welding
arc bridging the gap, and illustrating the substantial current that's
flowing. 

You'll have better results if you bury bare copper grounding wire, such
as #4 or #6 AWG going to your groundrods. Where it approaches your
satellite cable, run it at a right angles to the satellite cable to
minimize inductive coupling. Try to maintain at least 6-12" of vertical
separation where they intersect. Since your groundwire will be carrying
substantial RF current, it will tend to act as an antenna. The fact that
it's energized can easily be seen by bringing the glass portion of a
flourescent lamp near it. Keep it low to the ground as much as possible,
burying as much as you can. Minimize its length to reduce its inductance
and its effectiveness as an antenna. Hope this helps!

Safe coilin' to you, Alan!

-- Bert --