Re: GROUND - Verdict ? ? ?

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

Original poster: "Gerry Reynolds" <gerryreynolds-at-earthlink-dot-net> 

Hi Dan,

I'm one of the guys that said to connect the NST ground to your RF ground.
I was assuming that the NST was under your primary coil and no one would be
close to the NST.  Safety was less of a concern since even if the case were
to spike to 200 volts because of currents in the RF ground,  the risk was
negligible compared to exposed 15 KV bushings.  The assumption was that
anything dangerous would be bundled together and be operated with people
safely distanced.  I personally don't consider the added 200V potential
between the NST core/case and the NST's primary windings to be a breakdown
issue since the primary is not wound directly on the core (there probably is
a plastic bobbin between the core and winding), the enamel of even single
build insulation is good for several thousand volts, and the primary winding
is isolated from the case with very good feed thru insulators.

If you put your NST's in your control cabinet where you operate, the control
cabinet itself definitely should be grounded to the mains safety ground and
the NST's themselves should probably be also.  If you consider not grounding
the NST to the cabinet and mains safety ground, then RF ground would need to
be brought into the cabinet and tied to the NST case and I'm not sure I
would recommend this.  The two high voltages cables coming out to feed the
main sparkgap, Cp, and primary windings needs to be high voltage insulated
for safety.  The main spark gap needs to be physically next to the Cp and
Primary winding of the TC since these components carry high discharge
current and heavy conductors are important.  The connection between the NST
and the main spark gap is not a high current path (normally) and solid
conductor automotive spark plug cable will suffice.  The three terminal
safety gap still needs to grounded to the NST case as well as the Terry
filter.  These two components need to be in the control cabinet next to the
NSTfor best protection, in my opinion.  A two terminal safety gap could be
placed next to the main gap (in parallel) and adjusted to fire slightly
before the three terminal safety gap located with the NST if one was worried
about safety discharge currents going thru the spark plug wires (I suppose).
For your configuration, the only ground in your control cabinet would be the
mains safety ground and the only ground in the TC area (main gap, Cp,
primary, and secondary) would be RF ground.

You would need to guarrantee that there could NEVER be a secondary strike to
your primary circuit in this configuration, since severe impulse currents
could be conducted directly onto your mains and main safety ground putting
at risk any other electronic component plugged into the mains (even if
turned off) such as computers, home theater systems, etc.  Sufficient
spacing between the inner winding of the primary and secondary, and a strike
rail become even more important.

Hopes this helps,

Gerry R.
Ft. Collins, CO


 > Original poster: Dan <toodamtall1-at-yahoo-dot-com>
 >
 > Hi folks,
 > You all provide a great debate. It's awesome to be
 > collaborating with such excellent minds. You know who
 > you are.
 >
 > But what is the verdict on the ground? I'm getting
 > ready to wire up my control cabinet and I want to do
 > it right.
 >
 > My control cabinet (30A variac, 2 x 15/30 NSTs, 40A
 > line filter, 200mfd pfc, terry filter) will be 15 feet
 > from the tank circuit (conntected by #4 fine strand
 > welding cable).
 >
 > Thanks
 > Dan-Ft. Lauderdale
 > (yes the wife's settled down now, thanks to all who replied).
 >
 >
 >