[TowerTalk] Fwd: Grounding of tower

[Jim Lux]

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.