On Thu, 9 Sep 2004 23:45:44 -0400, "Jack Painter"
wrote:

http://www.cpccorp.com/deep.htm

See the data in that
paper above for some sample resistance measurements which they consider
"average"

Hi Jack,

Interesting link.

The paper offered was a model of terse reporting, sticking only with
the facts as best they could come by them, and little in the way of
overextending themselves with fanciful interpretations. The averages
were what they found for themselves, not abstracted and generalized to
the world at large.

I would suggest that they also made some cogent observations about the
soil structure that goes beyond myths and software passing as the new
age equivalent of old wive's tales. I would further observe that
making a declaration of what the resistance of ONE electrode is, is
farcical in the extreme. It would take two to tango and with that
second one added to measure the first, problems abound!

Especially notable is the 10 fold variation in reported electrode
resistance over a 4 year period, and the 10 fold variation of
electrode resistance within a survey group. Such an error range
easily eclipses what is taken on faith as "average ground." And then
we have to ask ourselves that embarrassing question, just how does the
mud in my backyard compare to "average?"

Your comments on
That means as close to
equipotential as possible, and it does not assume a good ground, or even any
ground at all in certain cases.
translate with fungible results to RF for the same reason. No one
here knows what quality ground they live over (really! to one skin
depth at HF?).

I would still like to know how many radials Reggie needs for his
several KOhm mud in his garden. No, I take that back, what I want to
know is what parameters he puts into the software that predicts the
number of radials - and why would it matter?

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Thu, 9 Sep 2004 23:45:44 -0400, "Jack Painter"
wrote:

http://www.cpccorp.com/deep.htm

See the data in that
paper above for some sample resistance measurements which they consider
"average"

Hi Jack,

Interesting link.

The paper offered was a model of terse reporting, sticking only with
the facts as best they could come by them, and little in the way of
overextending themselves with fanciful interpretations. The averages
were what they found for themselves, not abstracted and generalized to
the world at large.

I would suggest that they also made some cogent observations about the
soil structure that goes beyond myths and software passing as the new
age equivalent of old wive's tales. I would further observe that
making a declaration of what the resistance of ONE electrode is, is
farcical in the extreme. It would take two to tango and with that
second one added to measure the first, problems abound!

Especially notable is the 10 fold variation in reported electrode
resistance over a 4 year period, and the 10 fold variation of
electrode resistance within a survey group. Such an error range
easily eclipses what is taken on faith as "average ground." And then
we have to ask ourselves that embarrassing question, just how does the
mud in my backyard compare to "average?"

Your comments on
That means as close to
equipotential as possible, and it does not assume a good ground, or even
any
ground at all in certain cases.
translate with fungible results to RF for the same reason. No one
here knows what quality ground they live over (really! to one skin
depth at HF?).

I would still like to know how many radials Reggie needs for his
several KOhm mud in his garden. No, I take that back, what I want to
know is what parameters he puts into the software that predicts the
number of radials - and why would it matter?

they 'why' is the real question as there are several reasons to design a
'ground' and each of them has different requirements. a few examples with
different needs:
1. home electrical safety ground.
2. electrical substation ground.
3. hv transmission line ground for step or touch potential.
4. hv transmission line ground for lightning protection.
5. building ground for lightning protection.
6. building ground for rf isolation
7. vertical antenna ground for rf return
these are all very different problems requiring very different solutions. i
write software, part of which helps design grounds for hv transmission line
structures. the theory and practice in this area is quite different from
that used to design any of the other types (except maybe for small buildings
requiring lightning protection). And some of the extensive testing we have
done on the physics of the problem shows that the ground reacts quite
differently from what most people expect when trying to dissipate lightning
transients. i wouldn't use my software to design a ground for my station,
though i did use some of the results of our tests to convince myself that
what i did do would be adequate. Nor would i take any one other program as
gospel when designing a ground for any particular type of installation.
indeed at my station i have several different types of 'ground' systems,
raised radials under elevated verticals, wire mesh mats on the ground under
elevated verticals, ground rods at towers and service entrances, ufer
grounds in foundations, perimeter ground around the house, each for a
slightly different purpose and no one good enough for all the jobs that need
to be done. Some help with rf radiation from antennas, some are lightning
protection, and some are for ac safety. and they can't be interchanged in
most cases... and some of them would not fit most layman's definition of
what a 'ground' even is.

On Thu, 9 Sep 2004 22:16:35 +0000 (UTC), "Reg Edwards"
wrote:

|I am not very familiar with USA power-grounding regulations and they
|probably vary from state to state. But I am under the impression that in
|some simple circumstances, perhaps domestic, a single ground rod is
|considered adequate for safety purposes.
|
|Under similar circumstances a maximum ground electrode resistance ( whatever
|its construction ) of 50 ohms is specified.
|
|A 'standard' ground rod is 8 feet long and 1 inch in diameter.
|
|An average soil resistivity is 500 ohm-metres ( = 2 mS ). See Eznec?
|
|The calculated resistance of a single standard rod in average soil is 194
|ohms. ( I'm sure the calculating formula can be found somewhere on the IEEE
|shelves. There ought to be greater use made of it. )

I responded to this in more detail but the post never came through.
So more quickly this time see:

http://www.usda.gov/rus/telecom/publ...s/1751f802.pdf

[snip]