On 4/9/15 10:36 AM, Billy Watson wrote:
As understood in the N.E.C. concrete is considered as ground. An office on slab w/ground water issues, would be considered as an ideal ground.
The NEC grounding/bonding requirements are all about line frequency, which is a bit different than what we want for a tesla coil.
The NEC is looking at handling kiloamps from things like a power line short or a lightning impulse. You'll never have that kind of energy in a tesla coil (or, if you do, you'll have plenty of experience by then).
Ufer grounds are virtually required in all new construction. No using water pipes any more.
However, for a TC, what you're really looking for is a lowish impedance return path for the RF current from the topload and sparks. The important thing is that the currents be contained *near* the coil. If your ground connection is a 30 foot wire to some building ground point, then the current has to flow down that wire, radiating fields where you don't want them.
If you lay the counterpoise on the concrete floor, then any currents that aren't coupled directly to the counterpoise and flow through the concrete will be capacitively coupled to the counterpoise (counterpoise is one capacitor, the concrete is the other).
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