# [TCML] Grounding a Tesla Coil (Yes, Again)

Brandon Hendershot brandonhendershot at gmail.com
Sun May 9 21:32:38 MDT 2010

```Alright,
Sorry for the delayed response,
I didn't get any exact math to calculate the counterpoise size, but
the most I can safely get away with is 7.25' x 1.5' or 10.875 sqr/ft.
Will this work with a 3.5" x 16" secondary, 1007.7' of 29 AWG wire,
Thanks for all your guys's support,
Brandon

On May 5, 2010, at 6:01 AM, jimlux <jimlux at earthlink.net> wrote:

> Brandon Hendershot wrote:
>> Exactly how big should a counterpoise be in relation to the size of
>> the topload? I only really have about 4' of room available to the
>> coil because I have my drill press and alarm clock on their too.
>> That's 4' including the space used by my NST and variac, which are
>> both safety grounded in the case.
>
> Why not make the counterpoise flexible.. Think of a conductive rug
> that you can roll out when you're experimenting.  It could cover the
> drill press and clock and whatever..
>
>
>
> I imagine it would be problematic having the
>> counterpoise connected to mains ground...
>
> Why?  If you're concerned about RFI, then put a suitable RF choke in
> the connection.  But for safety, the counterpoise should be
> connected to whatever you might be touching, and that generally
> means "green wire ground" as well.
>
> Hmm, does the counterpoise
>> actually need to be wired to the secondary, or is there some sort
>> of coupling going on?
>
> Yes, it definitely needs to be connected to the secondary (i.e. the
> bottom of the coil).
>
> One more, I think it would really help me understand
>> how to construct a functioning artificial ground if I knew exactly
>> what an ordinary ground functions as under normal circumstances.
>
> Have you run one of the modeling programs that shows the electric
> field around the coil?
>
> Your secondary is basically a resonant LC circuit with the L
> (inductor) being the coil, and the C being the top load (one plate)
> and the surroundings (the other plate).   Like any circuit, current
> flows through the L and C, so that means that current flows through
> the surroundings.
>
> What a counterpoise does is give a low impedance path for that
> current to flow in.
>
> It also serves as sort of a limited faraday cage for things under
> the counter poise. That is, if a streamer comes out of the topload
> it will strike the counterpoise rather than what's under the
> counterpoise.
>
>
>> Thanks, I really appreciate all your guys' help,
>> Brandon
>>
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