In one of the Polyphaser documents they talk about the rise time and length
of a strike duration. Forget the details but the conclusion was that rods
further out than about 50' would not be effective because the strike would
be over before the outlying rods came into play.
If that's true then it seems there is an implied maximum density of the
field based on the 50' maximum radius for rods and the 2x rod length
spacing.
73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie
-----Original Message-----
From: jimlux
Sent: Friday, November 03, 2017 10:05 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Mot R36 related to NUMBER of installed ground rods
On 11/3/17 7:15 AM, john@kk9a.com wrote:
How is ground resistance measured?
With an AC ohmmeter specifically designed for this application. Mostly,
it's a matter of standard probes, standard measuring voltages and
currents, etc. so that everyone's measurements are the same.
googling "grounding system resistance testing" turns up lots of links:
http://www.esgroundingsolutions.com/how-to-do-electrical-grounding-system-testing/
http://www.weschler.com/_upload/sitepdfs/techref/gettingdowntoearth.pdf
http://www.aemc.com/techinfo/techworkbooks/ground_resistance_testers/950-WKBK-GROUND-WEB.pdf
there's a difference between measuring soil resistivity and grounding
system resistance, but the same kinds of measurement tools are used.
I'm sure you could use standard ham DMM and a variac + isolation
transformer to do something that is functionally similar.
The tricky parts are the standardized electrodes (that's just a matter
of getting the right length and diameter) and not having your
measurement perturbed by ground currents from other sources and
interference. Kind of like the problems with measuring an 160m antenna
when there's strong AM stations nearby.
John KK9A
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Mot R36 related to NUMBER of installed ground
rods
From: jimlux <jimlux@earthlink.net>
Date: Fri, 3 Nov 2017 05:52:59 -0700
"The contractor shall install sufficient ground rods in accordance with
document XYZ that the measured ground resistance is less than 5 ohms."
At the end of the job, the customer goes out, measures the resistance,
finds it's 4.2 ohms and says "you get paid"
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