RE: [TCML] RF Ground and Brass

["Lau, Gary" <Gary.Lau@xxxxxx>]

Hi Scott,

I think folks often go overboard with unnecessarily large RF ground cables and connections.  It's important to remember that the actual RMS current in these conductors is very small.  It may be useful to use a fat conductor for portions that are very long, as a means of minimizing conductor inductance, but I'm not even sure that this is critically important.  Minimizing the total conductor length to the ground rod(s) is probably the most useful point.  But for a couple feet or less from the secondary base to a central tie-point, it's pointless to use anything heavier than simple stranded #14 or #18AWG - it only needs to be heavy enough to not be fragile.  Same with the connection to the NST, Terry filter, and strike rail.  I don't think copper vs. brass makes any difference for the ground connection, but since wire is typically copper, I would use that.

The secondary base connection method advocated in the COILBUILD documents is silly.  These are very old documents and in need of revision.  Trying to secure a copper strap ground conductor to a copper plate, both subject to surface oxidation, with a rubber band, sounds like a very poor and unreliable connection.   I use a 1/4-20 screw connection to each end of the secondary, as both a mechanical and electrical connection.  See http://www.laushaus.com/tesla/secondary.htm  If you don't have access to press-fit threaded inserts, there are other ways using common hardware.

Your EMI filter hookup sounds correct.  My thoughts on the topic are at http://www.laushaus.com/tesla/emifilter.htm.

As for surge protectors in a power strip, I've always wondered whether they are attempting to protect against differential (hot to neutral) spikes, or common mode (ground to hot & neutral) spikes.  IMO, common-mode spikes are more likely, so I've added a couple of MOV's inside of my Variac case from hot & neutral to ground.

Regards, Gary Lau
MA, USA

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of Scott
> Sent: Sunday, March 02, 2008 7:49 PM
> To: tesla@xxxxxxxxxx
> Subject: [TCML] RF Ground and Brass
>
> Hi all,
>
> I hate to touch on two topics that are so widely discussed here, but I have
> a question that kind of falls into a gray area.
>
> First off, I'm on the last stage of my coils construction, the
> grounding. This topic has been fought over many times on the list (I just
> spent 2.5 hours reading over all the entries about RF ground) and have
> decided on the following scheme:
>
> Connections to RF ground:
> --Secondary Coil, follwing these insuctions :
> http://www.pupman.com/howto/COILBLD3.GIF
> --NST case
> --Strike Rail
> --"RF Power Ground" line coming out of Terry Filter.  (The "NST Ground" line
> coming out of the Terry Filter will go into the NST case I guess...refer to
> the Terry Filter diagram to see the lines I'm refering too ;) )
>
> Now the Mains supply will go like this:
> 1.) A power strip with a surge protector will plug into a wall outlet
> 2.) From the surge protector, a cable will go into a EMI Filter, from Tesla
> Stuff:
> http://cgi.ebay.com/RFI-EMI-Tesla-Filter-2-x-20-Amps-115-
> 250vac_W0QQitemZ140211303737QQihZ004QQcategoryZ7288QQssPageName
> ZWDVWQQrdZ1QQcmdZViewItem#ebayphotohosting
> The side with the 3 terminals will be hooked up to the output from the surge
> protector, with the center terminal being the ground.
> 3.) The side of the EMI filter with 2 terminals will run into the NST's hot
> and neutral inputs.
>
> Simple Enough right?
>
> Now the RF ground itself will be right next to the coil: outside, 4 steel
> spikes hammered 3 feet into the Earth.
>
> Now here's my question:
> I have this ribbon coming off the secondary coil and 10 AWG wire coming from
> the NST case and strike rail, how do I actually connect them all together to
> the physical RF spikes?  I was just gonna solder the ribbon to the spikes,
> and then thread the other wires through a hole in them.
>
> And a second question:
> For the metal grounding ribbon coming off the secondary, does it need to
> copper for sure?  I wanted to use brass instead.  At my hardware store,
> brass is 1/4 the cost of copper and available in more thickness's.  And does
> the ribbon need to go all the way from the secondary base to ground
> spike?  It would be 3 feet of ribbon that way even is the coil is right next
> to the RF ground!
>
> Also, the grounding on the Terry Filter seemed a little weird too, maybe
> someone could confirm could I'm doing it right as described.
>
> Sorry for the massive post again, but I have been piecing together this
> problem for the better part of the day, and would like some loose ends tided
> up.
>
> Thanks for all responses!

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