On 11/22/2012 9:01 AM, (PeteCresswell) wrote:
Per :
An interesting alternate method would be to have a
ground rod for the antenna and then use the cold water
pipe to bond it to the main grounding system of the
house. That way with a strike....

Sounds to me like there is no downside to a dedicated grounding
rod for the antenna - right under it where the ground wire drops
down the side of the house.... and then work out the bonding
possibilities with the rest of the ground system later.

Have I got it right?

The downside is that for a near strike, or strong surge current earthed
through the power earthing system, the rod can be thousands of volts
different from the building "ground". Those thousands of volts can show
up at anything connected to the antenna and power. I wouldn't add a
ground rod without bonding it back to the electrical system. But bonding
does NOT eliminate this problem, created by the distant rod. IMHO the
rod increases the probability of damage.

What the NEC wants now is the power system earthing connection to the
water pipe within 5 ft of where the water pipe enters the house. One of
the places for the rod bond to connect is in the same 5 ft. Years ago
the power system connection could be anywhere on the water pipe. My
preference generally is to connect the rod bond near the power service.

If lightning strikes the antenna, a ground rod will help only a little.
The earth potential at the ground rod will likely be many tens of
thousands of volts different from the building earthing and the building
"ground". The antenna will be even further. There will likely be major
damage. That can include arcing from the antenna or antenna wires to
elsewhere in or on the house.

Ask a ham with a high antenna what you have to do for lightning
protection. Earthing is only part of the protection. A major element is
that all wiring rises to the same potential during a strike. You can't
reliably do that with the distant (but bonded) rod. A start would be to
route the antenna wire into the house adjacent to the power entrance
with the antenna in a compatible location.

For most of us, it is real unlikely our houses (or antennas that don't
stick way above the house) will be hit by lightning, and is not
cost-effective to provide lighting protection.


Some principles:
I isn't easy to make connection to the earth. A ground rod is one of the
worst ways.

Two points of earth that are pretty close together can be many thousands
of volts different during an "event".

The ends of a wire, maybe 20 ft long, can be thousands of volts
different during an "event".