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Re: [TowerTalk] US Tower damaged by lightning

To: "Tower and HF antenna construction topics." <>
Subject: Re: [TowerTalk] US Tower damaged by lightning
From: K4SAV <>
Date: Wed, 28 Apr 2010 21:55:22 -0500
List-post: <">>
Jim, it sounds like you are doing a good job figuring out how the 
lightning got into the AC lines.  That path from the tower winch, into 
the barns doesn't sound too good to me, and may have been the source of 
most of your problem.   I recognized that path as a potential liability 
on my tower, and since my winch is only rarely used I chose to make it a 
plug-in arrangement and I have it disconnected except when raising and 
lowering the tower.   Of course I didn't need an inspection for my 
tower, and I don't know if an inspector would have bought that 
arrangement.   (It also pevents anyone from deciding to play with the 
winch controls at tower.)

Your tower ground rod installation sounds good. 

AC wiring underground is not immune to lightning just because it is 
underground.  I chose to add AC surge suppressors to my main AC lines 
even though they are underground.  Of course that is not worth much by 
its self, but it can't hurt, and it wasn't expensive.

As for N7MAL's statement:
"Jerry have you ever taken a 'direct' lightening strike?? I suspect not 
otherwise you would not have made this statement: "" You have a large 
amount of damage that should have not happened. ...."

Well you suspect wrong.  When I first erected my tower here in Alabama, 
I had three strikes on the tower in the first 4 months after putting it 
up.  No damage at all.  None since.  I do have some nice shiny spots on 
the mast extending out the top just for that purpose.  Lightning here in 
Alabama is not nearly as bad as where I lived before for 38 years, which 
was dead center of the highest lightning density area in the USA.  You 
learn a lot that way.  If you do a good job on a lightning protection 
system you should rarely ever get any damage for a hit on a tower.  
There are rare cases where it might decide to miss your tower and hit 
the house instead, and that would be pretty bad.  In Florida, I have 
seen it miss my antenna by 30 ft and hit a scrawny little 10 ft high 
tree.  There is no way to prepare for that kind of thing (it's rare, 
only saw that once) but you can fix a tower to take a hit.  However it 
is very easy to overlook something when configuring that system.  It 
sounds like maybe that's what happened to Jim.

Jerry, K4SAV

Jim McDonald wrote:
> Jerry,
> My questions really were about repairing the tower, but I welcome any
> suggestions on improving the grounding.
> The winch was connected to a dedicated 120VAC circuit with a GFI outlet at
> the base of the tower.  The lightning followed the conduit into a nearby
> barn to its subpanel and then split two ways - into another barn, where it
> took out an Invisible Fence (buried wire for dogs) and into the house via
> the conduit feeding the barn subpanel.  Another subpanel in the basement,
> located next to the service panel feeds the radio stuff.  The surge strips
> downstream from that were damaged, but the two computer UPS' and an APC line
> conditioner were OK.  The radio outlets and equipment are about 20' from the
> service panel.
> Two of the lightning radials are 64' long, with an 8' rod next to the base
> and rods each 16' after that.  They are buried a few inches.  The wire going
> to the third rod came out of the ICE connector block during the strike.  The
> wire continues on in a trench to the house, which is about 50' away, with
> two rods in that trench.  It continues two directions - into a basement
> window well with the grounding panel mounted on another rod and also to the
> electrical and telephone ground rods.  In total I have 17 or 18 ground rods
> all connected together.
> I wish I had service panel arrestors but didn't because we have underground
> wiring for phone and electric.
> The DirecTV antenna on the roof of the house, about 50' from the tower was
> zapped.  No TVs were damaged.  My wife's computer, connected to the router
> through probably 50' of Ethernet cable was damaged; the RJ45 plug was
> charred.  The Ethernet port in my shack computer in the basement was
> damaged, as was the 4-port serial card.
> In previous installations of this tower, the electric circuit to the motor
> was in PVC rather than conduit.  I just had the outlet replaced at the side
> of the barn, maybe 6' from the tower, and I will remove the buried conduit
> to the base so I won't have a path from the tower base into the electrical
> wiring.
> The phone box on the outside of the house exploded.  I think the lightning
> came up the ground wire to it.  The wireless Internet antenna on the side of
> the tower was damaged; the CAT5 cable was attached to an arrestor on the
> grounding panel and then to a Linksys router, which was destroyed.  The
> replacement wireless Internet unit is now on a roof tripod.
> I would have disconnected if we had any nearby lightning but there wasn't
> any.
> There was no other damage to the house or the two barns.  A couple of other
> GFIs popped, as did the main breaker feeding the service panel and several
> circuit breakers.
> Two next-door neighbors reported balls of light on the ground in back of
> their houses at the same time as my strike, which I assume were ground
> strikes.  They are each about 500' from me (I live on 5 acres).
> That's about it.  It was exciting - very loud, bright, and the house shook.
> We had smoke outside from around the base of the tower, and we had three
> fire engines here.  
> Jim N7US
> -----Original Message-----
> From:
> [] On Behalf Of K4SAV
> Sent: April 28, 2010 16:43
> To: Tower and HF antenna construction topics.
> Subject: Re: [TowerTalk] US Tower damaged by lightning
> You have a large amount of damage that should have not happened.  You 
> should really try hard to figure out why.  After you get all this 
> repaired, it would be nice to know why this happened and that you 
> corrected that problem that allowed that to happen.  Your insurance 
> company won't  be happy to see you returning for a second claim of this 
> size either.  It's difficult to make good suggestions just looking at 
> the pictures because it is difficult to see the "big wiring picture".   
> Making wild guesses is unlikely to help.  From all the burn marks on AC 
> outlets and the main AC panel, it is obvious that the AC wiring 
> conducted a huge amount of current thru your house. Try to figure where 
> the path is that allowed it to get there.  I can see one possibility of 
> it entering the tower control box and then down the AC wiring, but I 
> don't know where that wiring goes or how it is routed.
> I see the entrance panel but it is unclear where that is located.  It 
> appears to be inside the house somewhere.  I can't see how long the 
> ground wire is from the entrance panel to the AC service ground rod.
> I can see three ground wires leaving the tower but I don't know how many 
> ground rods are used.   In one picture it appears that one of those 
> ground wires (the stranded one) is blown in two.  Is that true (or just 
> an illusion in the photo)?  If so, I would want to know why.
> Look to see if there are any other burn marks on other objects outside 
> the house, like outside AC outlet boxes, water spigots, chimney (which 
> usually has a metal liner), roof vents, or even concrete walls (which 
> has rebar in many places).  Maybe there was a secondary finger that 
> attached itself to one of those items.   Also if for some reason the 
> tower ground was poor, the tower could have possibly been elevated to 
> such a high potential that a side flash occurred.
> Jerry, K4SAV
> _______________________________________________


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