Re: NST Ground, RF ground, the whole bit...

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

Original poster: "Jon Tebbs by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jgtebbs-at-eos-dot-net>

Hi Malcolm, Terry, Jonathon, All,

My comments below Malcolm's...

Tesla list wrote:
> 
> Original poster: "Malcolm Watts by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>
> 
> Hi Guys,
>          Comments at the bottom.........
> 
> On 12 Jul 01, at 19:45, Tesla list wrote:
> 
> > Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
> >
> > Hi Jonathon,
> >
> > "I" agree with you :-))  If it can carry seriuous RF, it needs a short RF
> > ground.  The AC line ground is only good for 60Hz AC stuff.  There are all
> > kinds of opinions on this, but this is mine ;-)
> >
> > Cheers,
> >
> >       Terry
> >
> >
> > At 09:13 PM 7/12/2001 -0400, you wrote:
> > >WOAH, wait a second! I thought the green ground (mains ground, 3rd
wire...)
> > >was for the power cab. only (with the RF mains filters, boxes, and
> > >whatelse...). The RF ground is for all others - NST case, motor housing,
> > >bottom of sec. coax shield (if aplicable) any faraday cages... Whats the
> real
> > >story? Whos the expert here?
> > >
> > >The only time I connect the third wire ground to the NST case is when I am
> > >using it for a Jacob's Ladder...
> > >
> > >---------------------------------------
> > >Jonathon Reinhart
> > >hometown.aol-dot-com/kidd6488/tesla
> 
> Is the transformer being asked to deal with RF or mains frequencies?
> With the case/core of the transformer connected to the RF ground, is
> the base current of the coil elevating the case of the transformer
> wrt mains ground or not?
> 
> Questions, questions ;)
> Malcolm

Malcolm, I like the way you make people think. Due to the inherent
inductance of
even a straight ground wire connection, the secondary base current will produce
a measurable voltage drop thus elevating the ground above _ground_ (wrt mains
ground). Why stress an NST's marginal insulation any more than necessary? All
mains connected devices would best be grounded to the mains ground. Those
devices that are intended handle RF should be connected to RF ground along with
the secondary base i.e.: the NST Filter/Safety Gap, Strike Ring, etc.

Some will argue that if a mains connected device can be struck by a
streamer/leader/arc, then it should be connected to RF ground. This, IMHO,
would
very unlikely _if_ attention is paid to detail in the design and layout
stage to
avoid the possibility in the first place. Consider this: when a lightning bolt
strikes ground, does the soil resistance create a voltage gradient from the
center out?

Then there is the misconception that EMI/RFI line filters should be connected
backwards. This one goes back several years in the list archives and was based
on whether the filter's intent was to keep RFI from getting into of or out of a
device, turn it this way or that. A review of the Corcom FAQ regarding line
filter design reveals that for a line filter to be most effective (have the
greatest loss) the input and output impedances should have the greatest
_mismatch_ to the line and load respectively. In short, the line side is
optimized for connection to the line, not the load. Wrt Corcom line filters,
they fall into two load impedance categories: those optimized for high
impedance
loads and those optimized for low impedance loads. One would be wise to check
the intended application of a surplus line filter under consideration for use.

The Corcom FAQ is available at:
http://www.corcom-dot-com/faq/rfifaq.htm

That's my (2*pi)/pi cents worth ;-)
-- 
Jon G. Tebbs
<jgtebbs-at-eos-dot-net>