RE: Grounding Question

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

Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

I'm going to put my 2 cents worth into this discussion because I
cannot agree with some of the opinions I've seen expressed here.

On 29 Oct 2003, at 22:06, Tesla list wrote:

 > 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.

You are not discharging 15kV into any ground - the gap actually
shorts the transformer winding. That is what it has to do if it is to
work as intended. I would always connect the transformer case to the
mains ground AND at the same time, ensure the secondary discharge
never hits the case (by providing an RF grounded screen or suchlike
for the transformer). I also take pains to ensure no primary
components are ever hit (strike ring, making the coil tall enough
etc.).

       The reason I would ground the transformer this way is to
minimize the P.D. between the core and windings. An RF ground can be
elevated considerably above the mains ground thanks to the high peak
currents present and the high reactance of the RF lead and ground at
the TC frequency but the transformer primary is referenced to the
mains ground, not the RF ground.

Malcolm

 > Rgs
 > Ian.
 >
 > -----Original Message-----
 > From: Tesla list [mailto:tesla-at-pupman-dot-com]
 > Sent: Thursday, 30 October 2003 12:49 pm
 > To: tesla-at-pupman-dot-com
 > Subject: RE: Grounding Question
 >
 >
 > Original poster: "Lau, Gary" <gary.lau-at-hp-dot-com>
 >
 >   >Original poster: "Mccauley, Daniel H" <daniel.h.mccauley-at-lmco-dot-com>
 >   >
 >   >The ground on your NST is a safety ground.  You should ground it to your
 >   >120VAC ground.
 >   >Not RF ground ! ! ! !
 >
 >   >Remember, the ground on the NST is primarily for safety.  You don't want
 >   >the chassis to become electrically hot
 >   >due to internal short.  Ground the NST to your 115VAC ground.
 >
 > 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
 >
 >
 >