Apparently Joe is talking about contact resistance between a grounding rod
and the soil. Is that correct, Joe? I also saw those ground rod clamp
testers in the Inet, and is still puzzled how they claim accuracy down to
0.01 Ohm.

Thks,
Ivan

On Sun, 4 Dec 2005 21:11:23 -0500, "Ivan Makarov"
wrote:

Apparently Joe is talking about contact resistance between a grounding rod
and the soil. Is that correct, Joe? I also saw those ground rod clamp
testers in the Inet, and is still puzzled how they claim accuracy down to
0.01 Ohm.

Thks,
Ivan


Accuracy as in reading + or - 0.01 vs reading of 0.01 ohms absolute -
very big difference in technology involved. ;-) You have to define
what they are doing.

Here is a couple of links, just the first two Google hits

http://www.extech.com/instrument/pro...ialMeters.html

http://www.stayonline.com/detail~ID~2048.html


"nothermark" wrote in message
news
On Sun, 4 Dec 2005 21:11:23 -0500, "Ivan Makarov"
wrote:

Apparently Joe is talking about contact resistance between a grounding
rod
and the soil. Is that correct, Joe? I also saw those ground rod clamp
testers in the Inet, and is still puzzled how they claim accuracy down to
0.01 Ohm.

Thks,
Ivan


Accuracy as in reading + or - 0.01 vs reading of 0.01 ohms absolute -
very big difference in technology involved. ;-) You have to define
what they are doing.

Well, yes that's true.. In this case I was talking about the NEC (National
Electrical Code).. Sort of a basic electrical question, from a ham radio
prospective. They put up a Satellite Internet dish on my roof and it was
too far away from the 'Service' protective ground so it's not grounded. So I
ran my own bonding ground wire to tie it into the rest of my single point
grounding system. It started me wondering just how affective all these
ground rods were, even though they are all bonded together. So that started
me looking around for a way to measure the resistance to ground, as I figure
the less the better. Of course, in this case I am talking about 'protective'
ground as required in the NEC handbook. The electricians around here eyes
glaze over when I ask about the 25 ohm or less requirement.

So I figured maybe someone on here had experience measuring the required
ground.. It would be my luck the house would take a minor lightning hit and
the Insurance company would try to weasel out of there responsibilities by
saying the ground didn't meet the NEC requirements not to mention I rather
not have issues. While unlikely, I hear all sorts of horror stories on how
they are trying to disallow claims for all sorts of reasons after Katrina.

Joe AG4QC

"Ivan Makarov" wrote in message
...
Apparently Joe is talking about contact resistance between a grounding rod
and the soil. Is that correct, Joe? I also saw those ground rod clamp
testers in the Inet, and is still puzzled how they claim accuracy down to
0.01 Ohm.

Thks,
Ivan

So I figured maybe someone on here had
experience measuring the required ground..

Well, not a lot of experience, but the keywords you're looking for are
"fall of potential".

Depending on which spec you're meeting, you drive multiple ground rods
in at distances that are large compared to the length of the rods.
Then you measure the resistance between the rods.

Just sticking your ohmmeter leads between two ground rods is not good
enough. There is a substantial chunk of 60Hz AC and probably some DC
current flowing in the ground and the little battery inside the
ohmmeter will generally add nothing. Fall-of-potential meters use much
larger currents (and usually measurement techniques, like using an AC
frequency unrelated to 60Hz and harmonics) to overcome this.

My impression with antenna installations that I've been peripherally
involved in is that NEC requirements (25 ohms) are generally easy to
meet unless you've got dry rocky soil. And that the 25-ohm requriement
is nowhere near good enough to protect your equipment/buildings from a
direct hit.

Tim.

It sounds to me like you are looking for legal advice, not technical
advice.

With that in mind, and a lot of bad experience with lightning, I take
the attitude that the NEC establishes the minimums for protection.
After all, what can an extra ground hurt?

Last summer I had lightning rods installed on my house. I live on a
low ridge and have taken several (expensive) hits over the last few
years. They installed ground rods on two corners of the house and tied
one of them to the service ground. They also tied the Antenna tower to
the opposite ground rod. I added another ground (#6 wire) from the
Cable TV ground rod to the service ground. I also tied the Cable TV
ground to the ground rod on the invisible fence (dog containment) with
#6 wire.

With all of that I still don't have a good RF ground. I hope to put up
a vertical antenna soon and the first thing I need to do is establish
a system of radials. Of course, the first wire will be a #6 to the
service ground.

BTW, I don't understand "too far away from the service ground to be
connected."

John Ferrell W8CCW

On Sun, 4 Dec 2005 21:06:16 -0600, "AG4QC"
wrote:

Well, yes that's true.. In this case I was talking about the NEC (National
Electrical Code).. Sort of a basic electrical question, from a ham radio
prospective. They put up a Satellite Internet dish on my roof and it was
too far away from the 'Service' protective ground so it's not grounded. So I
ran my own bonding ground wire to tie it into the rest of my single point
grounding system. It started me wondering just how affective all these
ground rods were, even though they are all bonded together. So that started
me looking around for a way to measure the resistance to ground, as I figure
the less the better. Of course, in this case I am talking about 'protective'
ground as required in the NEC handbook. The electricians around here eyes
glaze over when I ask about the 25 ohm or less requirement.

So I figured maybe someone on here had experience measuring the required
ground.. It would be my luck the house would take a minor lightning hit and
the Insurance company would try to weasel out of there responsibilities by
saying the ground didn't meet the NEC requirements not to mention I rather
not have issues. While unlikely, I hear all sorts of horror stories on how
they are trying to disallow claims for all sorts of reasons after Katrina.

Joe AG4QC

"Ivan Makarov" wrote in message
...
Apparently Joe is talking about contact resistance between a grounding rod
and the soil. Is that correct, Joe? I also saw those ground rod clamp
testers in the Inet, and is still puzzled how they claim accuracy down to
0.01 Ohm.

Thks,
Ivan



John Ferrell W8CCW