Eric Gustafson wrote:
> Hi Ed,
>
> Your post raises a number of questions for me. There isn't
> enough information to make sense of your findings. So that we
> can interperet your results, can you answer the following
> questions for us?
>
> 1. How did you make this measurement?
The measurement was made by placing one lead in the center of the
concrete block, with the other connected to an 8' ground rod 6' away.
> 2. What kind of measuring device was used?
A Fluke Model 7 Volt\Ohm meter.
> 3. How was the connection to the center of the base made?
Pressure applied to the lead.
> 4. What is the measured electrode connection resistance to earth
> for the rod?
Not sure what you're asking here, but from the earth to the rod is
about
.2 ohms
>
> 5. Does the concrete contact the earth directly or does the hole
> have some kind of liner (wood form, plastic sheet, etc.)?
Concrete connects to direct earth, however, a wood form of 2x10s is
still in place. Thinking about removing it tomorrow to expose the
sides.
One exception, I poured 4 inches of concrete into the bottom before
the main pour to make sure the rebar did not touch earth.
> 6. What kind of earth are we talking about?
Let me put it this way, solid rock hard clay. As a matter of fact, it
took 3 hours for a 14" bucket backhoe to dig the first 3 feet. It
finally became a matter of simply using the teeth and scratching. As
an aside, I had to dig a slanted hole for one of the guys to a 25G. I
used a pickax, post hole digger, 1" wood bit in an 1/2" drill, and a
piece of
steel rod to dig it. The clay is so hard it would stall the drill. It
took me 4 hours to dig a 4' hole in this way. The hollow steel pipe
was the best, drive it into the ground for a few inches with a full
sized sledge hammer, beat it loose, and then drive the dirt out of the
center with a piece of aluminum tubing. There is very little doubt in
my mind that if I could have screwed the base bolts into the ground,
concrete would not have been necessary. You can swing a pick ax as
hard as you can and it will penetrate about 3".
> 7. Did you make a similar measurement between two of the
> (otherwise unconnected) ground rods?
Not yesterday, but did today. Another test at 6pm this evening (
concrete now 54 hours old, ( made an error on time in the first post ,
the concrete was 30 hours old, not 36 ) and resistance today varied
between 950K to 970K between a common center point and all 4 ground
rods. That's a reduction in resistance of about 500K ohms in one day.
Weird...
More tomorrow, but please remember this is merely an observation over
time and no opinion is implied.
73
Ed
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