The article does say what the cause of this crack was. Here is what
"A word of caution: A Ufer ground consisting solely of the tower
foundation is a bad idea. Lightning surges passing through the
foundation can vaporize water in the concrete and damage the foundation
through rapid expansion of steam. An example of this unfortunate event
is shown in Figure 4. This particular tower had no earth electrode
system, other than the leg foundations."
Jim Lux wrote:
Paul Christensen wrote:
What exploding concrete?? Back up your claim with real life validated
proof. My experience has been the opposite.
Want evidence? See Figure 4 (and the text below it) in the link below:
The text says the only grounding was through the foundation and makes
no mention of whether it was a properly constructed CEGR (i.e. 20 feet
of conductor, etc.)
Also, the picture does not show whether a structural failure occurred
as a result of the lightning damage (the tower is still standing,
after all), or whether that's just surface damage. If it's a 1/8"
deep crack in the surface and doesn't penetrate, who cares? For all
we know from the limited data in the article there was a prexisting
crack in the concrete that was enlarged as a result of steam induced
Considering that Ufer did an awful lot of tests over the years, and
subsequent researchers have also done a lot of tests, I think that if
there actually was a realistic concern about spalling and exploding
foundations it would have shown up in the reviewed literature (as
opposed to in anecdotal reports or ground rod manufacturer sales
literature). I have no doubt that there are cases where there has
been lightning damage, but I would suspect that those don't fit in the
category of a proper concrete encased grounding electrode. For
instance, the "3 2 foot J bolts in the top of the footing" used to
bolt the tower mounting plate is probably NOT a suitable grounding
The article also sort of contradicts itself. On the one hand it
advocates external grounding systems, but then, it says that the
external 20 rod grounding system showed an impedance of 150 ohms, but
after bonding to the structural steel, the impedance dropped to 1 ohm.
Sounds to me like the steel was a better ground than the rods.
The article also mentions the "conduit as choke" thing, which I used
to believe in, but subsequently have not seen a good analysis to show
that it actually works, particularly for large surge currents, taking
into account the magnetic saturation of the steel.
According to NFPA 780, Ufer grounding is generally satisfactory
provided that it is not the only earth grounding mechanism and that
the ground is brought out beyond the concrete encasement to make the
Which section? (just curious.. I don't have my copy of 780 here)
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