Re: Thoughts on Tesla coil grounds...

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>



Tesla list wrote:
> 
> Original poster: "Paul Benham by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<Paulb-at-woodanddouglas.co.uk>
> 
> When using a ground plane like this, do you have to make sure that you
> keep clear of it as well as the coil itself, and treat it as if it was
> live with R.F.?


I suppose one should remain clear, and I wouldn't get within 4 feet of my
coil when its running anyway (the mesh only extends 2.8 feet from the
center anyway) to avoid those unpleasant "tingle in the fingertips" phenomena.

However, yes, I DO treat it as a true RF ground (or counterpoise).  It's as
close as you're going to get, especially compared to some wire strung along
to some ground rod 20 feet away.

As far as covering your garage floor... from a safety standpoint concrete
is probably just as good a conductor as the chicken wire, for all intents
and purposes, so you haven't lost anything by putting the metal floor down,
and you've probably gained, by providing lower impedance connection to the
bottom of the secondary.  Judging from the number of 60 Hz shocks I got as
a youth standing in bare feet on the concrete working on one project or
another, concrete is a plenty good conductor.

There IS a significant safety hazard from the chicken wire approach.  If
the chicken wire is grounded to the safety (green wire) ground, it provides
a low impedance path for 60Hz to travel to ground. If you happen to get
connected to the line (or, say the output of the pig, gods forbid), the
chicken wire will provide a nice return path for the current.  Things like
this are why ESD wrist straps have a 1Meg resistor in series.  If your
properly ESD grounded hand happens to touch a live wire, you won't die.

  This particular hazard could be safely dealt with by a simple technique:
cover the chicken wire with an insulating layer (say, 4 mil polyethyelene
sheeting).  It won't affect the RF properties or counterpoise
characteristics, but it will keep YOU from being grounded with a low
impedance ground when you stand on it.

> 
> I assume that you do not treat it as being a true R.F. ground, and
> covering my garage floor in this way and then standing on it with a
> running coil present would be a bad idea! - as I would be in contact
> with control gear grounded to mains ground.
> 
> Thanks in advance,
> 
> Paul Benham.
> 
> Tesla list wrote:
> >
> > Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <jimlux-at-earthlink-dot-net>
> >
> > On the other hand, the chicken wire ground plane approach (which is what I
> > use) connects the bottom of the 4"x20" secondary coil to a 4x4 foot chunk
> > of chicken wire laying on the floor.  Not only is most of the RF voltage
> > developed between the chicken wire and the toroid, but the capacitance from
> > the chicken wire to the ground is probably fairly high (I'll have to try
> > measuring it), and the sheet inductance of the chicken wire is probably
> > fairly low.  I DO have the chicken wire connected to the safety (green
> > wire) ground as well, but, by a fairly small gauge wire.  I have never
> > noticed any RF voltage on the chassis components, etc., although I haven't
> > measured it to be sure.