Topband: [Bulk] Re: RFI - and lots of it

[Grant Saviers]

Recently I put up a big new tower and a ground system for it and learned 
a few things.

The actual ground conductivity is a bit of a mystery and highly variable 
over short distances, so I bought a clamp on ground resistance measuring 
meter on ebay, a Chinese knockoff for $300.  It was quite informative 
about what was working and what not.  After a short learning curve, it 
worked well and would be a good investment to share within clubs, etc.  
(DY1000A Digital Clamp-on Grounding Earth Resistance Meter Earth 
Tester)  I checked into renting a meter and the one month rental was 
more than $300.

The new code requirement is for #2 awg to the rods from the 
panel/tower.  However after expressing skepticism about why this is 
necessary, I learned that this size conductor is essentially a ground 
rod if down about 10" in the earth as it is essentially a horizontal 
rod, just about as effective (surface area) as pounding a 10' rod into 
the earth.

I started off believing I could drive two 10' x 5/8" rods with couplers 
to 20' depth with a 1.5" capacity Bosch hammer drill with a ground rod 
driver attachment but that was a no go.  I drilled the first 36" of the 
rod position with a rotary bit as we have a hardpan layer at about 12" 
to 24" depth.  Five new rods were 10' and one of 4' when going deeper 
was a no go.  The recommended spacing is 2x the ground rod depth and in 
a star configuration for towers.  The code specified resistance to 
achieve for a tower is less than 10 ohms.  I measured each lead and the 
resistance reduced by an average of 35% from late summer bone dry 
conditions to after about 4" of rain.  8.0 ohms to 5.3 ohms net parallel 
resistance for 5x 10' plus 4x 8' rods.   I believe that much of that 
resistance reduction after 4" of rain was from the #2 horizontal runs, 
about 90' of wire.  So I declared victory, and will measure again 
shortly now that we are well into the rain season here in Redmond, WA. 
and the ground is becoming saturated at depth.

Cadweld "One Time" copper thermite welding is the way to go for 
connecting the ground lead to the rod - good for the life of the rod w/o 
any need for inspection and zero ohms.  They are about $12 a shot from 
your local electrical distributor.  There are many variations of number 
and size of conductors.  They also appeal to any pyro instincts you 
might have.  For problem sites e.g. rock ledges, there are conductive 
concrete mixtures that can be poured around horizontal rods and wire 
leads to dramatically increase the conductive surface area and produce a 
useful ground resistance, but that is not needed at my site.

My reference "far earth ground" for measurements is the Ufer foundation 
of a steel building, about 250' of perimeter concrete. It is impossible 
to measure that resistance since the steel frame connects everything to 
everything, including the service transformer with HV underground 
feeder.  When that transformer was installed the PSE "ground" was the 
concrete vault Ufer, no separate ground rods. I suspect the net of these 
Ufer grounds are less than 1 ohm to the "far earth ground."

While my QTH is in one of the lowest lightning frequency areas of the 
USA, the new tower goes 50' plus over the tree line and is on a ridge, 
so I became a bit paranoid about a strike.  The total investment for the 
ground system was about $850 including the meter.  That seemed like 
reasonable insurance considering the rotators, hardline, controllers, 
and shack equipment dependent on a good ground system.

Grant KZ1W

On 10/29/2015 7:43 AM, Paul Christensen wrote:
> That's one reason why I like to augment a NEC-required mechanical connection with silver-solder.  The mechanical connection will degrade with time but it will take significantly longer for a silver-soldered connection to degrade, absent some really acidic soil condition.
>
> Local code here now requires two (2) grounding electrodes at the service entrance spaced to cover the "sphere of influence."  That means two eight-foot rods require 16 ft. spacing.  As I recall, the 2008 issue of NEC allows one electrode if one can demonstrate 25-ohms earthing resistance.    Not sure if that's still true with the newest NEC changes.   But what measures 25 ohms today may measure a lot higher as time goes by.
>
> Paul, W9AC
>
> -----Original Message-----
> From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Dan Edward Dba East edwards
> Sent: Thursday, October 29, 2015 10:28 AM
> To: Matt Murphy <matt at nq6n.com>; Tom W8JI <w8ji at w8ji.com>
> Cc: Jim Murray <adkmurray at yahoo.com>; low bad reflector <Topband at contesting.com>
> Subject: Re: Topband: RFI - and lots of it
>
> I, for one, wonder how good my service entrance ground is...mine is probably 20 years old, and while the top looks ok, there's no way to know what's going on down 4, 6 and 8 feet...my utlities are underground, if that means anything...
> as a starting point, should a guy drive a new one? or 2 or 3, spaced some distance apart?
> ( gosh, top band sounds lousy this fall, for me, anyway...sigs are well down from normal strength..) 73, w5xz, dan
>   
>
>
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