RE: Grounding Question

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

Original poster: "Lau, Gary" <gary.lau-at-hp-dot-com> 

You're welcome.  But in the interest of complete disclosure, I should point 
out that there are good reasons to consider a mains-ground connection to 
the NST case that have not been addressed in this thread.  Neither solution 
is perfect under all circumstances, but I feel that the RF ground is still 
the best compromise.

Consider that even a very good RF ground is not perfect, and the connection 
from the coil to the ground will have inductance and AC resistance.  This 
means that the voltage at your coil's RF ground connection will not be a 
flat line, but rather will have very high voltage spikes relative to "true" 
ground.  And, relative to your mains ground.  No one to my knowledge has 
actually measured this, but I suspect it's many hundreds (maybe more?) of 
volts.  So even without any safety gap firings, there will be high voltage 
between the NST case (assuming it's connected to RF ground), and the mains 
neutral terminal.  The primary-to-core insulation was probably not designed 
to endure this level of HV transients, so this is a concern for RF-grounded 
NST cases.  However, I've never actually heard of an NST failing with a 
primary to core short.  Maybe it happens and no one's been silly enough to 
grab hold of the NST case with one hand and a ground with the other with 
power on?

Gary Lau
MA, USA


Original poster: "Ian McLean" <ianmm-at-optusnet-dot-com.au>

Thanks Gary,  this clears up a matter of confusion for me.  I was getting
worried that I was doing the wrong thing connecting my NST cases to RF
ground after reading some posts here about grounding the NST to mains
ground, but logic seemed to dictate to me that, well, if my safety gap
fires, then I am dicharging 15,000 volts into mains ground which could fry
household mains equipment.

Rgs
Ian.


Original poster: "Lau, Gary" <gary.lau-at-hp-dot-com>

I can't see touching the case of the NST, ever, when the coil is operating,
as I'd likely be hit with streamers from the top load.  Even without
streamers, it's just not a good place to put your hands.

But more importantly, consider what happens when the safety gap fires.  The
center terminal of the safety gap is connected to the NST case, so you're
suggesting connecting it to AC mains ground.  Should a streamer hit the
primary and cause the safety to fire, the connection you propose would
discharge that streamer to your mains ground.  I think it's better to
channel such events through the RF ground, which is why I advocate
connecting everything to RF ground.

Gary Lau
MA, USA