Re: Random TC Questions

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Jim Lux" <jimlux@xxxxxxxxxxxxx>


----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Thursday, March 17, 2005 6:30 AM
Subject: Re: Random TC Questions


> Original poster: "Gerald  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
>
> Hi Jim,
>
> I'm studying your reply carefully trying to understand a different point
of
> view.  I'm glad you didn't use building code in your arguments cause all
of
> my sources seem to indicate that the code applies to the building and any
> permanently installed electrical equipment.  The TC (I believe we both
> agree here) is not in any way building code complient considering the
> exposed hazardous voltages (primary, secondary, etc).  Perhaps it is
useful
> to talk about two situations:  inside where earthground may not be close
at
> hand, and outside where it is available.

True enough, the building code (or, more commonly the NEC) generally applies
to permanent stuff (although "cord connected" stuff gets covered, as do
certain temporary installations).

The safety grounding aspects are more the province of "good engineering
practice" and the requirements imposed by testing labs such as UL.   There's
also good grounding info in a few IEEE specs.

Your distinction is a good one.  If you are indoors, the "ground" that a
person is connected to (by capacitance, if nothing else) is a bit trickier
to figure out than standing out in your driveway.

In any case, you want the RF currents to flow where YOU want them, not
somewhere else, and particularly not through the building wiring system.
However it's also important to think about what fraction of the RF current
is carried by the streamer (a small amount, I'd venture).  Most of the RF
current (which is what will cause the problems) is just capacitively coupled
from topload to the other end of the secondary.


>
>
> If INSIDE, the floors are of questionable grounding and if they conduct
for
> any reason (wet wood, concrete), a fault could make them hazardous with
> respect to ground.  I think this may be a good reason for an artifical
> counterpoise that is well grounded.  If people are standing on the
> artifical counterpoise (and they dont need to be), it would be safer to
> have it grounded to the green wire if other things in the room are
grounded
> to the green wire.  In general, high power coils probably should not be
> inside, but if they are, the artifical counterpoise should probably be 3D
> (to protect the walls, floor, and ceiling from a strike that could start a
> fire.  One thing that should be realized is that the green wire goes back
> to the breaker panel where it connects to neutral.  This node is then
> grounded to earth by a connection to a water pipe (existing code when our
> house was built) or to a rod in the ground (apparently todays existing
> code). Therefore a counterpoise grounded to a waterpipe or to a rod in the
> ground can be the equivalent of the safety ground.

Except that it wouldn't meet regulatory scrutiny.  While clearly TCs aren't
something contemplated by regulation, the thinking behind the regulation is
still valid.   You want the shortest possible path for the RF, and you want
to avoid loops (hence the prevalence of "star" or "tree" grounding systems).
If you have some wiring in the field of the TC (and there is), you'll get RF
coupled to it.  Much better to have the return path directly to the coil by
bonding your counterpoise  locally, rather than routing the RF through the
wiring to the panel ground, then to your ground rod, then back up to your
coil.


>
> If OUTSIDE, your counterpoise is earth and the TC should be directly
> grounded to it.  If all objects and persons are at a safe distance, there
> is no fault that can raise anything outside this safe distance to a
> hazardous voltage.

As long as you can maintain that "safe distance" you're good to go.  This is
more challenging in practical terms than one might think.