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RE: grounding question



Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 06:01 PM 10/9/2006, Tesla list wrote:
Original poster: "Lau, Gary" <Gary.Lau@xxxxxx>

I agree that a counterpoise would benefit by a connection through an RF
choke to safety ground, to establish a path for fault currents.

I have two separate RF grounds that I connect together when running my
coil.  In the front of my garage is a simple 8 foot copper clad ground
rod, with 6 inches above the ground.

About 10 feet away from that ground rod, on the side of the garage, we
had an addition built, so I buried a horizontal 8-foot length of 3/4"
copper pipe on top of the concrete foundation footing, about 5 feet
deep, with a vertical 3/4" copper pipe up to the surface, in contact
with the foundation wall.

Our breaker panel is grounded to the water pipe entering the house, plus
an independent ground rod.

If I try to read the resistance between either of my buried RF grounds
to the mains ground, I get a reading of over 4 Meg Ohms.  If I try to
read the resistance between the two RF grounds (about 10 feet apart), my
DMM reads open circuit!  I live in Eastern Massachusetts, and the soil
about my house is rocky fill and well drained, but by no means a desert.
It's not at all clear what benefit such a high impedance connection has
to 60 Hz concerns.

I think my RF grounds are fairly reasonably constructed by most
standards, but I have no faith that they would safely ground a fault
condition.  So this brings me to my point (thank you for reading so
far!) - How to construct an RF choke between the RF and green-wire
grounds that can support a fault current and still isolate RF from the
mains ground?


A dozen turns of wire on a FT240-31 core might do the trick. #43, or #77 material would probably also work It's many K at 2-4 MHz. Somewhat less at 150 kHz, but still probably enough to keep the worst of the trash off the wire.

Of course, then, the counterpoise will be at some RF potential relative to someone standing on the floor, and you could still get a RF shock/burn. But that's an issue regardless, especially with small coils, where the resonant frequency is higher.