Re: Ground box

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

Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

Hi Malcolm and Ray,

Ok, I tested it ;-))  A bit more boring than just guessing but... ;-))

Here is the scope voltage (1V p-p top) and current (20mA/div bottom) across
the inner, outer, and both conductors of the 40 feet of RG-8U coax as
compared to 22 feet of 3 conductor plastic covered 12 gauge "Romex" house
wire I had around (I used all three conductors).  I put 1 volt peak to peak
across the cables with my wide band amp and swept the frequency from 100 to
600kHz linearly.

http://hot-streamer-dot-com/temp/Cables100-600.gif

As expected, the inner conductor of the coax alone is a bit worse.  The
coax "sings" with harmonics in the coaxial cable a bit.  But really, not
too terribly much difference.  At 200kHz they all run about 70mA peak to
peak to give around 14 ohms of AC resistance.  Since the coax is twice as
long as the Romex, one may think it is a bit better.  However, the
inductance of the cables simply as a function of length and maybe how I
have them piled up is probably just as much of a factor.  Just check out
the VI curves across the Romex at 200kHz ;-))

http://hot-streamer-dot-com/temp/ELItheICEman.gif

To reduce the "impedance" you would have to go to ribbon or wide copper
pipe to reduce the inductance per unit length.  The pure resistance of the
bulk wire seems to not be a factor at all.  Sort of a case of the "ICE man
commeth" ;-))  Before anybody asks, I did put a low inductance resistor in
place of the cable and the V and I were perfectly in phase :-)  The Romex
cable has 10.85uH of inductance (probably a little coiled on the floor).
With that inductance no other wire type of similar size, length, material,
routing, etc. is going to be any different.  Once the cable is big enough
to handle the fault currents.  it is a mater of inductance...

I also ran them from 10kHz to 110kHz:

http://hot-streamer-dot-com/temp/Cables10-110.gif

The coax is a little more jittery but they are the same for any practical
purpose.

So with 14 ohms and running say 6 amps peak in the secondary base, I would
drop about 84 to 100 volts across the cable.  Not a big deal.

I would think using the inner conductor for the secondary base with the
outer braid of the coax as a floating shield would radiate less noise since
that wire is just a long antenna.  The coax does have some singing
harmonics but not really anything to worry about I would think.  The outer
braid seems to be able to conduct currents perfectly well.  There is
nothing wrong with the Romex other than I thought the coax would be better
for the RFI shielding.  Basically, it looks like one big heavy wire is the
same as the next.

Cheers,

	Terry

If I "really" wanted to have fun.  I would get some of that expensive
high-end audio speaker wire and compare it to the Romex I pulled out of the
trash. :-)  I looked on a few of those fancy audio sites for such
"scientific" frequency response information...  I didn't find any.  Heheheh
:-))))  

Sorry, even Terry has his buttons... ;-)



At 02:56 PM 4/6/2001 +1200, you wrote:
>Greetings Terry,
>
>On 5 Apr 01, at 18:13, Tesla list wrote:
>
>> Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>
>> 
>> Hi Malcolm,
>> 
>> I am using the outer braid of the heavy coax (it is braided) for
>> things like motor case ground, NST ground, safety gap ground.  I would
>> be using the center conductor (heavy stranded wire) for the "RF"
>> ground for the secondary base.  Thus, the low frequency stuff like AC
>> faults and such would go through the outside braid while the RF
>> currents go through the center conductor.  I was thinking the radiated
>> RFI from the long secondary base ground would be somewhat shielded buy
>> the outer braid.  It was just one of those thoughts that "looked" good
>> so no guarantee that it is any good...  Perhaps, the RF strike rails
>> and safety gaps should go to the center conductor too?
>> 
>> Cheers,
>> 
>>  Terry
>
>Something inside me says there could be problems with this approach. 
>I think it would be an idea to do some Z measurements on both 
>conductors to ground before proceeding. Someone has already blown up 
>mains equipment by mixing grounds. The capacitance between the braid 
>and inner is significant at high frequencies. If you wouldn't mind 
>taking the time, I'd be very keen to see what measurements say about 
>this. I'll put it on my "to be done" list as well but it could be 
>quite a while before I manage to get it to the Out basket. Far too 
>many distractions for serious coiling investigation at the moment 
>unfortunately.
>
>Best Regards,
>malcolm
>
>