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Re: Random TC Questions

Original poster: "Gerald  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Jim,


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.

INSIDE: The path of the base current is the easiest to figure out since it is almost all conductive. The RF conduction current into the TOP LOAD (if I remember the current profile correctly) is about half the base current. The other half has bled off in the form of displacement current before reaching the top. The RF current leaving the top in the form of conduction current in the streamers and displacement current must be equal to what reach the top from the coil. Certainly, any RF current leaving the coil secondary will find its way back to the coil base somehow and a "3D" counterpoise is the best way to control the path while inside. It will keep all the RF currents confined to the volume of this counterpoise and protect all building surfaces from a strike. This counterpoise should then be green wire grounded. Inside operation without a counterpoise of some sort becomes very iffy for larger powered coils and for small power coils, care needs to occur to keep the coil away from surroundings.


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).

This is true whether inside or not. If outside and you use the natural counterpoise of earth, you ground the coil to earth to provide the most direct path to the base and therefore must not ground to greenwire to avoid the loop.



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.

Agreed. For inside operation, the RF current resulting from any house wiring in the field of the TC will find its way back to the coil base somehow, either by traveling out to earth ground and coming back via an earth ground connection to the coil base or by traveling from the wire to the TC control panel and to the the coil base via the green wire ground connection to its base. The only way to prevent these currents from traveling on the house wiring is to keep the wiring out of the TC field (use a 3D counterpoise while inside). Anytime an artifical counterpoise is used (whether a flat plane or a 3D cage), it should be bonded directly to the base of the coil. The base should be the central node for any star connections.




> 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.

Certainly one needs to think about the "sneak" path such as the coil arcing, say, to a poorly grounded gutter that conducts to a person standing next to it. Thats why I included objects being at this safe distance.

Thankyou Jim for you in depth response. You helped me better think about this important issue and I hope others have benefited from it as well.

Take care,
Gerry R.