"Rick (W-A-one-R-K-T)" wrote in
news

On Sat, 14 Jul 2007 02:04:34 +0000, Owen Duffy wrote:

You will see articles on the net describing drilling a hole with a
hose
and a peice of pipe. I have reservations about this, because it is no
longer a drive electrode. I have not seen this method used by
commercial
applications and I suspect that if one was contracted to drive
electrodes, this would not be an acceptable method.

Good evening, Owen.

Good morning Rick,


I am unsure what you mean by "it is no longer a drive electrode" and "I
suspect... this would not be an acceptable method".

Certainly the earth's grip on the ground rod will be much less tight
this
way, but only for a little while... over time, won't the earth shift
with
weather and rain and such, so that eventually (in days or weeks) it
will
grip the ground rod sufficiently well?

Or am I missing your point? (No surprise there...) :-)


I should have said it is no longer a driven electrode.

Over a long time, it probably becomes equivalent, but in the first
instance, it is in less intimate contact with the ground.

It has been my experience with voltage operated ELCBs and loose earth
electrodes that they are unreliable and cause false tripping at quite low
leakage currents which I attributed to a variable resistance, and they
were usually fixed by driving a decent electrode.

You will find lots of discussion about the merit of boring a hole,
placing an electrode and filling it with bentonite or kitty litter or
some other enhancing material. Some hams assert that they water the
electrode (plain tap water or urine or both) as a conductivity enhancer,
I think that is more an excuse for consuming 807s.

If you read performance data for a driven electrode, it doesn't
necessarily apply to an electrode in a bored hole and then backfilled,
whether by slurry or compaction or whatever.

I am not saying they don't work when done in that way, but they are
different and quite likely to be poorer than driving the electrode.

For a multi mode RF / AC protective / Lighting ground, shallow buried
radials might be more effective than one or several driven electrodes
anyway. A driven electrode (or any vertical electrode) is not very useful
for RF.

Someone commented to the effect that a vertical electrode that hits rock
is a waste of time. That depends, the ground above the rock may be much
wetter than for the presence of the rock, it which case the shorter
electrode might reach more conductive earth and be good. However a short
electrode in dry sandy soil that strikes rock may be quite high
resistance and recourse to buried strip electrodes is warranted.

I drove an electrode at a holiday cottage at the coast (where it rains)
and it hit a serious rock shelf at 2.1m. The electrode measured very low
resistance at 1kHz, much lower resistance than I expected from a single
2.4m electrode in clay. I attribute that to the rock shelf serving to
drain ground water down the hill and presenting quite wet clay in the
region above the shelf.

Owen