On Mon, 23 Jan 2006 10:25:26 -0800, Richard Clark
wrote:

On Mon, 23 Jan 2006 07:29:11 GMT, Owen Duffy wrote:

I created a graph to add to an existing web page from the functions
for 3mm (bare) wires buried 0.1m

Hi Owen,

Does this discount the proximity of the radials nearest the center?
That is, the graph is not simply a summation of the individual
lengths, is it?

Richard,

See my response to Reg.

The functions are from the reference paper you identified. I don't
recall that they explained the derivation of the functions, and they
may even be fits to experimental data. They do not appear to do
something as crude as summing the individual lengths.


What would nominal be (in other words, actual) for this specific
description above?

Did you mean "normalised"? You need to multiply the %/m value from the
Y axis by the actual soil resistivity in ohm-metres to get the
resistance of the electrode. For example, if you look the chart up for
3 radials of 5m length, you get 15%, which is multiplied by soil
resistivity (say 50 ohm-metres at a location) to get expected
electrode system "DC/AC" resistance of 7.5 ohms. (The graph is part of
a larger article which explains my "normalisation".)

Interestingly, I note the ref doc recommends galvanised electrodes. I
have been conducting an experiment here where I have recorded the
resistance of several driven earth electrodes over some years, and a
galvanised electrode of 25mm OD performs much worse than a copper clad
electrode of 13mm OD driven just 300mm away from it (both 2.4m long).
(The galvanised electrode is not electrically bonded to the earth
system for reasons of galvanic corrosion).

Owen
--