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]