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Re: [TowerTalk] Lightning Damage and Insurance

Subject: Re: [TowerTalk] Lightning Damage and Insurance
From: "Roger (K8RI)" <>
Date: Thu, 29 Apr 2010 20:22:43 -0400
List-post: <">>

Dick Green WC1M wrote:
> This response is partly about the details of a significant lightning event
> and partly about the insurance company's response. I'm giving you a little
> more than you asked for because I think the details provide good background
> for the insurance discussion and may be of technical benefit to you and
> others on the reflector. 
> We had a massive surge a couple of years ago, not long after I completed
> installing a new 110' Rohn 55 tower. I don't believe the tower was hit
> directly, but picked up a tremendous amount of induced energy from a nearby
> hit on a tree in the woods. 
There are a lot of "it all depends' when it comes to lightning protection.
There is absolutely *nothing* a person can do that will guarantee 100% 
protection for everyting in the house or on the property from lightning.

As Jim said, and I think he covered it pretty well, even with the so 
called single point ground you are only minimizing the likely hood of 
damage. As was pointed out, we need to stop thinking of lightning as 
just DC. The very steep rise and fall times of the lightning *strokes* 
creates a relatively wide range of frequencies centered around 1 MHz +/- 
an octave or so and that is for normal lightning. Each strike is 
composed of many strokes going up and down.  Think of them as a "really 
ratty" square wave with ragged rise and fall times and lots of "ringing".

Another point is the best protection does little or may even makes 
things worse if not properly installed
 with a well designed ground system.  The home owner can purchase the 
best protection, but if just one part of the grounding system is not up 
to par, or connected in the most efficient manner, the whole thing falls 
to the weakest link.

Even the routing of the wiring in the home or shop can make a tremendous 
difference.  It's typical for wiring in older homes to be "daisy 
chained" so the outlets in one room are on the same circuit as the 
lighting in another room. There will be multiple runs from the main 
panel, up through the nearby walls and through the attic where they go 
into junction boxes. From these them may go to wall switches and ceiling 
lights. The neutral may or may not follow the same path down to the 
switch and then to the lights. From there that same circuit may to to 
another junction box and down through the walls of another room to the 
outlets near the baseboard. Quite often the bathroom would get stuck 
onto one of these runs. It's not uncommon to find the outlets in one 
room on the same circuit as the outlets in an adjacent room with a 
common wall. Possibly only that wall is common and the rest of the 
outlets in the one room are on a different circuit.

A prime example of the above is the room in which I'm currently 
working.The outlets in the wall in front of me (behind the computers) 
are common to the bathroom which is on the other side of the wall. ALL 
the bathroom lights and outlets are common to the outlets in the next 
room to the South and those are common to the lights in the living room. 
There is little logical order in the pathway for the circuits. There is 
even less logic to the path followed by lightning. Put too much series 
reactance in its way and it'll just go some where else. Often it'll get 
off a perfectly good conductor to jump across open air, or out of 
conduit to follow what appears to be a random path through the earth.

However in this example the computers are at the end of about a 50-60 
foot run while every thing else in here is at the end of a 20' run.  
OTOH that really doesn't make much difference as the computers are hard 
wired (CAT6) to the ham stations in here and in the shop. (about 130' 
run and different electrical system.)  The shop computers are not just 
on a different circuit, the shop is on it's own power feed from the 
electrical company. 

Even though the systems all tie into the elaborate electrical ground for 
the towers there can be no single point ground as equipment in the house 
hooks to equipment in the shop and vice versa. Both the shop and the 
house have a ground system that goes nearly all the way around them.  
Just a little more work and they will both be inside the circle.

One point I'd like to make is that even with all the direct hits the 
tower has taken with no damage to any thing in either the shop or house, 
the next one could take out most of the electronics in both. Lighting 
strikes are as unique as individual humans so I have no way of 
predicting whether all the work and money I've put into a ground system 
will be met with another typical strike, or one that is atypical. Worse 
yet, the next one could be one of those "super strikes".


Roger (K8RI)


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