On 5/10/13 7:09 AM, Patrick Greenlee wrote:
Grant, interesting link on copper corrosion. The use of salts,
including table salt (sodium chloride) has been suggested as well as
sulfates such as Epsom Salts to improve the conductivity between
grounding structures (ground rods etc.) and the soil. The copper
corrosion write up mentions chlorides and sulfates in the soil as
sources of corrosion for copper. Another one of those things that make
you go hmmm. What is better, corroded copper in soil seeded with
sulfates and or chlorides or or lower conductivity soil with less
corrosion on the copper?
That's why there's a whole raft of issues with "chemically enhanced
grounding electrodes" and that, among other things, is why the industry
and codes have, by and large, moved to concrete encased grounding
electrodes for the vast majority of applications. Herb Ufer invented it
because all those other techniques had problems.
If you want an admixture for grounding, bentonite is popular,
non-corrosive, and hygroscopic.
Chemical grounds are used where there's some special need and a more
conventional and reliable ground won't work. You have to maintain them,
and periodically check the ground resistance to see if you need to add
more chemicals or replace the electrodes. Measuring resistnace in these
situations is not just hooking up the VOM to the rod, either.
it's not really whether, in a one-off situation, you can come up with a
better ground. You almost always can. It's what do you use for the
99.99% of the time that is straightforward, simple, works well, and
requires zero maintenance and inspection. For new construction, you
can't get much simpler than laying a wire in the hole before you pour
the concrete.
If you were installing a grounding system on an existing historical
structure, that's when you look to more exotic techniques. If you were
told to go figure out how to put grounds on Thoreau's shack on Walden
(assuming it still exists), they probably wouldn't be wild about you
digging up the ground and pouring yards of concrete.
However, even in those sorts of situations, simple techniques tend to be
used. A few years ago I saw some 1000 year old 5 story high wooden
pagodas in Nara, Japan, and their lightning protection was basically 4
AWG10 wires going to what appeared to be Ufer grounds set about 20 feet
away from the drip line of the building. (one also notes that the
things survived for many centuries with no lightning protection, in a
very lightning prone part of the world..)
http://en.wikipedia.org/wiki/K%C5%8Dfuku-ji
Why the affinity for Cadweld in the NEC? One possible explanation is
that the NEC has to be applied by the rank and file of the electrical
tradesmen. Cadweld gets good results with minimally trained and
experienced personnel. The connections can be inspected satisfactorily
by marginally trained personnel.
Actually, I would say that the typical electrical trade worker is fairly
high skill, so it's not a matter of picking a method that requires less
training and skill.. I'll grant you that the typical electrician has
different skills than the typical welder. I wouldn't expect an
electrician to do good welds, but I also wouldn't expect a welder to do
good electrical work.
A more important consideration is that exothermic welds, as produced by
the manufacturers produce a very consistent connection, regardless of
the external environment. There's no issue with whether the correct flux
and rod are used (as with welding), there's less issue with things like
wind and contamination. You can do a one-shot in the rain and in a
muddy ditch.
Then there's the whole metallurgical aspect: it's all copper when it's
done. No worries about CTE mismatch and temperature cycling. No worries
about dissimilar metals and corrosion. No worries about acid flux residue.
There is also the whole "convenience" aspect. A typical electrical
contractor isn't doing any welding or brazing, and doesn't carry the gear.
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