[TowerTalk] Earthing a tower

[Jim Lux]

On 1/2/13 8:39 AM, K8RI wrote:
> On 1/2/2013 10:12 AM, Jim Lux wrote:
>>
> I haven't found the one on the NWS event yet, but there is a comment
> about half way down on
> http://forums.mikeholt.com/showthread.php?t=131113
> by  dereckbc referring to a telecom site grounding to minimum spec.

Yeah, I saw that one.. it wasn't clear whether the 4AWG copper wire was 
installed correctly


>
>
> The NWS event I was referring to was part of a Sky Warn training session
> a couple of years back, but I have little sense of time so all I can say
> for sure is that it was probably some time in the last ten years.  I've
> not found the specific photos I was referring to, but all I did find
> appear to be related to moisture getting into the metal/concrete interface.


that seems to be a common thread in failures.

I suppose that if you had a failure like this (spalled concrete), 
compared to, say, a rod that didn't make good contact with the soil, 
you'd never see the "damage" buried with the rod, while the concrete 
damage is obvious.

And, of course, neither says anything about whether the thing that was 
being protected was damaged, or the relative cost to repair.  You could 
be in a situation where the rod grounding electrode survives, but the 
equipment it's "protecting" is destroyed, or conversely, the concrete 
spalls but the equipment survives.



>
> Third row down on (Depending on your screen resolution) shows a pier pin
> tower base with a chunk blown out http://www.bing.com/images
> /search?q=concrete+damage+by+lightning&qpvt=concrete+damage+by+lightning&FORM=IGRE
>
>
>

the one at ecm-web.. the guy anchor with the Ibeam sunk into the pier?
http://ecmweb.com/content/upgrades-tv-station-tower-ensure-247-operation

later on the bing page I found a better article with better pictures
http://www.copper.org/applications/electrical/pq/casestudy/a6137/a6137.html

ALong with the comment that the problem was that the rebar wasn't 
adequately bonded, but that the quasi Ufer ground was so much better 
that lightning took that path (causing damage) rather than the 
conventional driven rod.

And I love this quote:
"Finally, we pulled out and inspected the grounding electrodes at the 
anchors and found that several of the exothermic welds had failed. 
Several conductors were also broken, possibly by earthmoving equipment 
during construction. With all these problems, plus the poor connections 
and high ground resistance, it’s no wonder lightning ignored this part 
of the grounding system!”

Breaking a weld is quite the chore... what did they do, run a bulldozer 
over it.

Another interesting quote at the end of the article:
"Copper is cheap insurance compared with the equipment damage that could 
occur if the system is inadequate."

This is where the difference between a ham installation and a broadcast 
installation is most evident.  At a multi million dollar installation 
that has a 24/7 requirement, the decision to spend a few thousand 
dollars on big copper and ring grounds etc is fairly easy.  They spent 
more on labor than on the copper most likely.  But that's a different 
cost and risk model than most hams would use.