Re: NST protection and grounding

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

Original poster: "Stephen Conner by way of Terry Fritz <teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>

At 12:28 02/06/03 -0600, you wrote:

>>3.) The old Q:
>>     Where should the NST be grounded: RF- or line-ground?
>>     Here my guess:
>>In order to protect the NST, it is better to connect to the line-ground, 
>>because, by that way, the voltage difference between the line neutral 
>>(connected to the primary)and HV-center tap is minimized. But, on the 
>>other hand, in order to protect the line (-and what's connected to it), 
>>from incoupling of ground strike noise, it is better to use the RF ground.
>
>I use RF ground.  I am not concerned about the 60Hz "safety" ground 
>here.  I am trying to stop the RF.  A good RF ground will also be a good 
>60Hz ground.  A small voltage difference between the RF and line grounds 
>does not hurt anything.

What if your RF ground sucks and there is a huge difference between it and 
line ground? I've mostly used chicken-wire groundplanes without any direct 
connection to anything and have seen sparks jumping between the groundplane 
and other 'grounded' objects, such as the tires of my bike that was sitting 
nearby. However, spark output from the coil was perfectly good, so I 
assumed the chicken wire was doing the job even though there was probably a 
few thousand volts of RF on it.

What I'm trying to say is that I think you can make a ground that's good 
enough for Tesla coil RF but completely useless at 60Hz. On this evidence I 
decided to ground all the parts of my NST, safety gap, and filter (if I had 
had one) to the line ground. I think that someone working with a 
small/medium coil in a second-floor apartment, for instance, might be in a 
similar situation.

On a related note: In some wiring systems (called PME=Protective Multiple 
Earthing in the UK) the 'ground' of your line can be a dangerous potential 
relative to real ground that you would get from an earth rod in the yard. 
If you connect the two together you could end up with the neutral current 
from half your neighbourhood flowing through your rig, which is not cool. 
Ham radio handbooks have (or should have) more to say about this.

Steve C.