RE: grounding NST's

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Qndre Qndre" <qndre_encrypt@xxxxxxxxxxx>

Hey Neal,

the way of grounding seems to depend on several factors.

Grounding a center-tapped (midpoint-grounded) NST 
to the mains "greenwire" ground will cause it to 
have half of it's output voltage at each terminal 
in reference to ground while the two hot wires 
from the output are 180° out of phase. It will 
also make it's case theoretically (!!) "safe to 
touch". This may not be an important factor since 
during normal operation no one will come into 
contact with any part of the transformer while 
it's live since this is not a good idea even when 
grounded to the mains ground which may be a very 
poor ground for RF currents. Strikes from the 
topload to the transformer's core as well as RF 
due to firings of the safety gap or filtered by a 
Terry filter will be channeled to mains ground 
which may cause damage to sensitive equipment 
such as computers or sensitive instruments as 
well as disrupting radio or television reception 
due to radio frequency interference.

Grounding a center-tapped (midpoint-grounded) NST 
to RF ground will also cause it to have half of 
it's output voltage at each terminal in reference 
to ground while the two hot wires from the output 
are 180° out of phase but the case and core will 
not be "safe to touch", even not theoretically, 
since RF ground may be at a high potential caused 
by RF currents from the secondary (which is 
almost ALWAYS grounded to RF ground). Any RF 
current from filters, safety gaps or impacts from 
the topload will be channeled to RF ground and 
normally not cause any harm to equipment if the 
RF ground is adequate for your coil's size.

Grounding one bushing of a true isolation 
transformer to RF ground ("single-ended") will 
cause it to have all of it's voltage at the hot 
(ungrounded) terminal in reference to ground. 
Most isolation transformers will not need safety 
gaps. A Terry filter is not suitable for 
transformers which are not midpoint-grounded.

Operating a true isolation transformer in a 
"floating ground" condition (which means it's 
secondary winding does not have any reference to 
ground) will make you able to ground any part of 
the circuit which is important if you want to 
perform measurements. This is rather unusual and 
is said to cause unforeseen behavior.

Using water pipes as RF ground for the NST as 
well as the secondary may cause damage to your 
telephone which is sometimes tied to the water 
pipes as well as making each and every object 
which is connected to the water pipes "unsafe to 
touch". Water pipes are in most cases the best RF 
grounds available. Make sure that no one in the 
building will come into contact with the water 
pipes or equipment connected to those including 
your telephone while your coil is in operation.

Operating a center-tapped transformer in 
"single-ended" or "floating ground" condition may 
damage it permanently. Do this only with true isolation transformers.

Regards, Q.

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To: tesla@xxxxxxxxxx
Subject: grounding NST's
Date: Mon, 20 Mar 2006 10:52:49 -0700
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Original poster: "Neal Namowicz" <mr_neal@xxxxxxxxxxxx>

The more and more I read your questions and 
answers, the more I realize how little I know! 
But, anyway, here's another question for y'all, 
that I've seen varying answers to.
When using an NST, where should I ground it to? 
Or should I ground it at all? At the moment, mine 
is grounded to the house ground, instead of RF 
ground. Then I've read somewhere where someone 
said NOT to ground the NST's. FWIW, I'm told by 
my family that the TV upstairs barely shows any 
interference at all when the coil's running, but 
would grounding it to the RF ground eliminate 
even more of it? Your suggestions, as always, would be greatly appreciated.

Neal.