Re: [TowerTalk] Mot R36 related to NUMBER of installed ground rods

[Clay Autery <KY5G@montac.com>]

Mmmmm.... the speed of light is REALLY REALLY REALLY fast...  The speed 
of current through big copper is still REALLY fast...  50 feet?  
Nah....  Rise time and duration for WHICH part of the strike event?  
It's not a single pulse...
And the 2x rod spacing is a guide...  rod spacing depends on the soil 
conditions...  And nothing says you can't space them closer... IN FACT, 
there are conditions under where it is likely advisable to do so...
73,
Clay, KY5G


On 11/3/2017 11:58 AM, Jeff wrote:
> 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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> >
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