On 1/21/2015 1:53 PM, Jim Brown wrote:
On Wed,1/21/2015 6:57 AM, Roger (K8RI) on TT wrote:
It has been my experience that "Mother Earth" does not supply a very
low resistance path, even with a large grounding system of multiple
ground rods and lots of, large, bare Copper wire. Much depends on
your soil conditions, but do not be disheartened if you see more than
1 or two ohms. Others may have had different results.
Right. The earth is a big resistor whose conductivity varies widely
from one place to another. I've measured in the range of 50 ohms
between two 8 ft copper clad steel rods about 12 ft apart, driven with
only an inch showing. This was at the base of my big tower. This was
with a DC VOM. As Jim Lux noted, not an ideal method.
I've mentioned this before, bit I think it's relevant to this discussion.
When I lived a mile S of Breckenridge, MI My station was in the
basement. The station ground was just on the other side of the basement
wall(Maybe 8 feet of copper wire to the ground. The house service
ground was about 50 feet straight West. About 75 feet straight W of
that was my 40 Meter 1/4 wave vertical with a ground rod under ir.
there were only 4 bare copper radial (slightly over a 1/4 wave long) So
essentially the station had two ground rods tied to the station ground.
Rephrased, the station has two grounds in parallel about 50 feet from
the service ground.
The photos in http://www.rogerhalstead.com/ham_files/boatanch.htm came
some years after the 101B , but it was located pretty much in the same
place as the KWM2 and Ten Tech stations which were not grounded/earthed
a whole lot better, but the electrical system did tie the neutral back
into the panel grounds.<:-))
The exciter was a Yaesu FT-101B. The Yaesu power cord was a two
conductor cord with a two pin, polarized plug.
The cord connected to the exciter through a 4 pin Jones plug and socket
with the male end mounted on the chassis. Inside the chassis the Jones
connector had to wires of about #10 soldered to the connector with a
very generous amount of solder. It was a very nice looking solder
joint even with the generous amount of solder. The only problem was that
with a little side pressure on the power cord, tht generous solder joint
could make contact with the chassis. Now the neu8tral "SHOULD" have
tied to ground in "the panel", but apparently it did not. As there was
no ground wire to the exciter e4xcept the station ground. Ground was
through two 8' ground rods through about 50 feet of wet soil to the
service entrance ground.
The problem with the station ground ans lack of continuity of neutral to
ground was not known to me at the time, but I was getting very close to
discovering it!
The radials for that 40 meter vertical just kay in the ground. They had
a 90 degree bend aboit5 8 to 12 inches from the end, The radials were
pulled tight and held by that piece stuck in the ground which made sense
at th time. The radial to the S had come loose, so I pulled it tight
and knelt down to stick the end back in the ground. THAR was when I
discovered the problem! When my knees touched the wet soil, "it had
me"! My muscles tightened up and I had a really good grip on the wire.
Almost as good a grip as it had on me. Fortunately my weight was not
centered and I(* fell over backwards. As soon as mu knees broke
electrical contact with the wet yard it let go of me and I had enough
sense left to throw that bare copper wire before I hit the wet ground.
My arms, legs and back muscles were sore for days, but at least I was
around to appreciate them.
With the 120 VAC tied directly to the station ground it didn't draw
enough current to trip the breaker. This was before GFIs were required,
but with no ground for reference a GFI would not have worked anyway.
One bac at the panel might have. Remember, this was in 67 and many
things were not required and few areas in the country required inspections.
Unlike the elaborate station and tower grounds here (The 3 towers "over
there" were not even grounded) and SPG did not exist. I'd not even
consider a system like that today, but that was 48 years ago. I'd like
to think I'm a bit smarter now, or at least a bit better educated.
We'll let the "smarter" bit remain unanswered. Lets just say, there was
a lot we hams didn't know back then.
Unfortunately the current test standards leave much to be desired with
new hams having to rely on codes, inspectors, and local hams for wisdom,
so we should try to look over the shoulders of new hams installing new
equipment and hope we have learned enough to offer advise that will aid
them in avoiding the dangerous pit falls that we often escaped from
through sheer dumb luck. I hope I've learned a lot since the station in
Breckenridge!
The point is, that the ground was a high enough resistance that it
didn't pull enough current to trip a breaker So it definitely was well
over 6 ohms 120VAC/20A=6
73
Roger (K8RI)
73, Jim K9YC
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73
Roger (K8RI)
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