For what it's worth, you will find the ground rod resistance calculations in
the IEEE Green Book, that's where the rule of thumbs come from on ground rod
spacing verses length. Lots of other good grounding stuff there too.
73
Mike King, PE - KM0T
-----Original Message-----
From: RFI [mailto:rfi-bounces@contesting.com] On Behalf Of EDWARDS, EDDIE J
Sent: Monday, January 19, 2015 11:24 AM
To: 'Rik van Riel'; rfi@contesting.com
Subject: Re: [RFI] w7ekb & ground rods
Rik,
In quick scan couldn't find anything on NEC Article 250 supporting your
statement. Did you find anything in 250? I only found a reference to "6 ft
minimum" distance, but that might be old reference and depend on length of
the ground rod. This makes sense for NEC since it's worried more about AC
electrical safety not RF grounding. In comm buildings R56 calls for using
both an underground ground ring/buss and bonded ground rods as a single
system bonded together.
However, your statement about rods closer than twice the length being
unproductive is true. It is a waste of money and has little effect on
ground resistance, but I doubt it does much harm if any overall. And the
"two-times length" maximum is also true.
I'd rather have any and all above ground, bonding connections from/to each
service (AC, cable TV, ham radio, telephone) as short of a run as possible
to the earth (e.g. buried, bonded ground rods) even if that meant the 8 ft
rods were only 6-8 ft apart. This would be required for an RF single point
ground system as I know it.
These are interesting NEC links for those with time on their hands:
http://www.necconnect.org/resource/?Id=1000027&Asset=c67370a9-8aa8-4606-a9c9
-bb631a89c2e2
http://fyi.uwex.edu/mrec/files/2011/04/W4.-Biesterveld-NEC-grounding-MREC201
0.pdf
73, de ed -K0iL
-----Original Message-----
From: RFI [mailto:rfi-bounces@contesting.com] On Behalf Of Rik van Riel
Sent: Saturday, January 17, 2015 11:09 AM
To: rfi@contesting.com
Subject: Re: [RFI] w7ekb & ground rods
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
On 01/15/2015 04:45 PM, EDWARDS, EDDIE J wrote:
> Excellent point Jim. All services' grounds (AC, telephone,
> television, internet and ham shack cable entry point & ham tower) must
> be bonded to a single-point ground system. There's no limit on number
> of ground rods as long as they're bonded (i.e. tied to the same
> grounding system). 8 foot ground rods need to be within
> 16 ft of each other, but can be closer if needed to shorten cable run
> to each service ground connection.
I thought NEC specified the opposite, specifically that ground rods had to
be at least twice their length apart, in order for each rod to have its own
independent connection to ground.
In other words, ground rods spaced closer together than twice their length
will not result in as large a reduction in ground resistance as ground rods
spaced the recommended distance.
- --
All rights reversed.
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