[TenTec] ground

[Dr. Gerald N. Johnson, electrical engineer]

I KNOW that ground connection is what the NEC requires. I don't agree
with it. I believe that the RF ground and the AC ground should only be
connected when RF burns require it, otherwise the tower ground shall be
isolated from the house ground at all times, separated by as much
distance as possible, including gaps in the coax cable connections. A
few tens of KV voltage drop from a few kiloamps into a 25 ohm tower
ground leaves enough voltage to jump a few inches. Been there, done
that, lost quite a bit of equipment that wasn't connected to anything at
the time. I do better isolation now. Grounding everything together,
including the power distribution system, also leads to small voltages
between grounded electrical equipment, such as milking parlor equipment
and the earth that leads to unhappy cows on occasion. Just takes a few
volts to a wet teat to cause a LOT of trouble. Isolation is the only
sure cure but its in violation of the NEC and the NESC.

Where the grounding is taken far further than a mere #6, grounding
sometimes is effective for repeater sites to keep lighting out of the
equipment. But there the building has to be surrounded with ground rods,
then a sheet of copper, at least 18" wide that ALL coaxes are grounded
to while passing through coaxial gas tube discharge devices, all radios
and radio racks are tied to that copper strap, and the power line and
phone line entering the building passed THROUGH that copper strap, going
through gas tube discharge protective devices. Then until enough
lighting hits the tower to melt the sand around the ground rods into an
insulating glass, the system works, even during storms. Its of benefit
if the building is made of steel, not wood. Any scheme less robust just
invites lightning to destroy the equipment, which it does with
regularity on the plains.

The NEC grounding requirements depend on the earth being as conductive
as a slab of copper which it is NOT. And depend on low frequency events,
not lightning.

73, Jerry, K0CQ

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