RE: What gets connected to RF ground?

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

Original poster: "Lau, Gary by way of Terry Fritz <teslalist-at-qwest-dot-net>" <Gary.Lau-at-hp-dot-com>

Comments interspersed:

 >> I have been doing research on grounding and
 >> what you ground to
 >> what (ie RF ground and mains ground) and I have
 >> found some conflicting
 >> advice.  On a number of web sites, the
 >> recommendation is to ground the
 >> bottom of the secondary as well as the center tap of
 >> the NST, and the
 >> center ground of the safety gap and filter
 >> capacitor.

 >The RF ground would be rather noisy with its
 >connection to the TC secondary, I think.

The RF ground IS indeed noisy.

 >> Another site says
 >> that only the secondary gets the ground and the NST
 >> and safety gap and
 >> filter get house ground.

 >This is what I do. Ground the center of the xmfr to
 >house ground, and the TC sec gets the RF ground.

There is some controversy here.  Most coilers including myself connect the 
NST case, safety gap ground, NST (secondary) filter ground, strike rail, 
and secondary base to RF ground.  The Variac case is the only thing that 
should connect to the 3rd wire mains ground (not neutral).  The reason that 
I don't connect the NST case to mains ground is that should there be a 
streamer strike to the primary, LARGE RF currents will flow through the 
case ground connection.  I want this to go to the RF ground, not my mains 
ground.

 >> Another variation of the
 >> latter is the you leave
 >> the NST center tap ungrounded.

 >BAD IDEA. The NST can be unbalanced and you want each
 >side outputting as equal voltage as possible. Also the
 >center ground gives the NST a reference, otherwise the
 >core may be hot.

I don't see the unbalance thing - both sides of an NST are essentially the 
same within a few percent.  No current flows through the center tap.  But I 
fully agree that the core needs to be referenced to ground.  But having 
said that, I must also point out that the RF ground that I advocate tying 
the case to is itself VERY noisy.  There will be a lot of RF capacitively 
coupled to the primary windings.  It's remarkable that we don't see 
primary-to-core breakdown from the high voltage transients that exist on 
the RF ground.  The level of RF on the core and primary is the reason that 
EMI filters should be used..

 >This sounds good too. Just be sure that the neutral
 >has a low impedance connection to ground, otherwise
 >everything connected to the variac case may be live.

'nuf said about neutral vs. ground connections...

 >> Another question is where should the Line filter be
 >> placed to filter RF
 >> from the house wiring?  As close to the NST's as
 >> possible or should it be
 >> with your variac and control box.  Depending on
 >> where this goes, what
 >> should it be grounded to (RF or house)?
 >> And why do
 >> they say you should run
 >> this filter backwards?  I think I read on Gary Lau's
 >> site that running it
 >> backwards is wrong.

 >I don't think that running line filters backward will
 >hurt it, because they're supposed to be symmetrical.
 >But I wouldn't recommend it.

What I was saying on my web site 
http://www.laushaus-dot-com/tesla/emifilter.htm is that the correct hookup, 
forward vs. backwards, depends upon what kind of ground you are hooking the 
filter case to.  If you connect the case to RF ground as I did, the "LOAD" 
side must go to the NST.  If you connect the filter case to the mains 
ground, the NST would go to the "LINE" side.  The best solution would be to 
use two filters.  One at the controller between the variac and the cord to 
the NST primary, with the filter case to mains ground and the variac output 
going to the "LOAD" terminals, and one at the coil between the cord to the 
controller and the NST, with the filter case tied to RF ground and the NST 
primary tied to the "LOAD" terminals.  There may be some filters that are 
symmetrical, but all that I have run across are definitely not symmetrical.

Regards, Gary Lau
MA, USA