Here is a good overview technical article that discussing earth grounding
and how to measure it. This info is for 60Hz AC system and equipment
grounding saftey and protection grounding, not antenna ground systems.
Be sure to look at the pictures and figures.

http://www.duncaninstr.com/Gr_article.htm

Here is another useful paper. Item number 14, Ground System Testing.

http://www.kilowattclassroom.com/ArchiveCatalog.htm

Ronnie, N5CSE

"AG4QC" wrote in message
...
I was wondering if anyone built some sort of ground resistance tester? I
read that the NEC requires 25 Ohms or less.. But I don't understand how to
measure that. I certainly could use a ohm meter between a ground rod and
the test subject, but then the ground rod I use as a reference could be
faulty.. It seems to me it must be measured in some other manner. Maybe low
frequency signal and then measure how much it's absorbed in the earth?.. I
know they sell a clamp on ground resistance tester for big bucks.
Considering it's a clamp on, it certainly don't have any external
reference.. Anyway, I was wondering if anyone had any experience with these
testers and maybe building one?

Joe AG4QC

Please ignore my earlier posting. I saw NEC and thought the reference
was to the program of that name (Numerical Electromagnetics Code). The
other responses caused me to re-read your posting more carefully and I
see you're referring instead to the National Electrical Code. 60 Hz
measurement is of course what you want to do, and my response was
entirely inappropriate in that context.

Roy Lewallen, W7EL

"Roy Lewallen" wrote in message
...
Please ignore my earlier posting. I saw NEC and thought the reference
was to the program of that name (Numerical Electromagnetics Code). The
other responses caused me to re-read your posting more carefully and I
see you're referring instead to the National Electrical Code. 60 Hz
measurement is of course what you want to do, and my response was
entirely inappropriate in that context.

Whew, thanks, Roy, I thought you'd finally "lost" it! (hi hi and grin)
I wish I had something more solid to contribute, but I do remember my
USAF days when the aircraft parking ramp static grounding rings required a
scheduled resistance inspection, the date stenciled in black on yellow
circle. The resistance had to be below 10,000 ohms. The instrument the civil
engineers used to make the measurements was hand cranked, something like the
"Megger" used for insulation break-down testing. I cannot say whether it was
a regular "megger" or a specialized instrument.
Anyhow, we mechanics tried to do our own testing with an ordinary VOM
and found the task quite vexing. One problem was that stray currents in the
ground drove the ohmmeter crazy, and as if that wasn't enough, the ohmmeter
probes current caused an electrolytic (?) reaction, sort of like trying to
measure the resistance of a battery using a standard VOM.
Now I'm going to back up and read some of the references provided by
previous responders.
Old Chief Lynn, W7LTQ (I still like Furuno, Roy!)

"Lynn Coffelt" bravely wrote to "All" (07 Dec 05 00:24:56)
--- on the heady topic of " Ground resistance tester"

LC From: "Lynn Coffelt"
LC Xref: core-easynews rec.radio.amateur.homebrew:89630
[,,,]
LC The
LC instrument the civil engineers used to make the measurements was hand
LC cranked, something like the "Megger" used for insulation break-down
LC testing. I cannot say whether it was a regular "megger" or a
LC specialized instrument. Anyhow, we mechanics tried to do our own
LC testing with an ordinary VOM and found the task quite vexing. One
LC problem was that stray currents in the ground drove the ohmmeter crazy,
LC and as if that wasn't enough, the ohmmeter probes current caused an
LC electrolytic (?) reaction, sort of like trying to measure the
LC resistance of a battery using a standard VOM. Now I'm going to
LC back up and read some of the references provided by previous
LC responders. Old Chief Lynn, W7LTQ (I still like Furuno, Roy!)

Speaking of electrolytic reactions....
I would try a tool from the tv service industry called an ESR meter.
It measures the internal resistance of electrolytic capacitors by
using an ac signal of moderate frequency around 100K Hz. They can
typically measure from 0.09 ohms to 199 ohms.

A*s*i*m*o*v

.... Useless Invention: Flashbulb tester.