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Re: [TowerTalk] exploding foundations

To: K4SAV <>
Subject: Re: [TowerTalk] exploding foundations
From: Jim Lux <>
Date: Fri, 14 Sep 2007 10:22:59 -0700
List-post: <>
K4SAV wrote:
The article does say what the cause of this crack was. Here is what they said:

"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."

The problem I have with the statement is that there are some things not stated:
a) did that foundation actually have a Ufer ground? or, was it just bolted to the bolts protruding from the concrete? And, if the latter, did those bolts have sufficient length in the concrete, and good connection to the tower. Ufer's papers (and others since) make the point that just bolting structural steel to bolts sticking out of the foundation doesn't necessarily make a good grounding connection, hence the idea of the 20 feet of AWG 4 copper wire that you see in the NEC.

b) A single narrow crack doesn't really look like the kind of damage seen from steam explosions. It might just be the camera angle, etc., but pictures I've seen of actual cases where spalling and fracture occurred look more like large hunks blasted out of the side, and you can see the bolt or rebar in the bottom of the hole. I'd want to see a good picture of the top of that footing, or a section cut through the footing. And, of course, a surface crack does not a failure make.

I've also seen a fair amount of the kind of effects from an exploding wire in a surrounding material,and it doesn't look like that. However, I never tried concrete as a surround, so it might be different.

I've seen fractures resulting from large electromagnetic forces from high currents, and they don't look like this either (and in any case, the force between two wires carrying a current in the same direction tends cause them to pull together)

Upshot is that the text and picture don't provide enough information.


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