I have a friend ready to put up a new tower and we're planning the grounding
system.
How about placing a big ground plate at the bottom of the hole for the tower
foundation before pouring the concrete? Should the tower, ground plate and
the rebar cage be connected together? Good or bad idea?
73 Bert, VE3NR
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of K8RI on TT
Sent: Sunday, April 17, 2011 5:12 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] grounding quesitons: Ufer, strap, exothermic welds
On 4/17/2011 2:06 PM, David Gilbert wrote:
> Again?? Seriously? That myth has been debunked so many times, both
> here and elsewhere, that I can't believe people are still perpetuating
> it. I've issued this challenge several times before and nobody has
> ever responded ... please quote one single URL or technical document
> that describes a verified instance where lighting passing through a
> proper Ufer ground , or any conductive element inside a buried
> concrete structure whatsoever, cracked the concrete. You'll find
> instances where a direct lightning hit to the OUTSIDE of a block of
> concrete caused damage (buildings, bridge abutments, etc), but not via
> a Ufer system of sufficient size and construction.
A while back I watched a training film from either NWS or NOAH that showed a
lightning strike that had not just cracked, but blown part of a system apart
BUT and and emphasize the but, stranded wire (either 0 or
00) had been used and it was in a wet location IIRC. Just what happened they
weren't sure, but it was an extremely rare event and I think we need to keep
in mind there is no 100 % guarantee against lightning, no matter what we do.
That means we *always* end up playing the odds and approaching diminishing
returns as we make our systems more robust and costly.
OTOH every proper step taken increases the odds in our favor.
Considering the odds I'd not worry a moment about tying the rebar in the
concrete to the grounding system.
I think it's a positive in our favor rather than a negative.
I would make sure the rebar did not come within 3 to 6 inches of any surface
of the concrete (code requirement I believe) and I would prefer solid copper
instead of stranded, but even stranded can be sealed.
> Check out the I.C.E. technical note on the subject if you don't
> believe me. It's not difficult to find on their website ... it even
> uses the word "myth" in the subject title.
I think they are wrong to call it a myth, but it's such a rare event AND the
procedure actually increases the odds in our favor so, it would not be a
concern for me.
> Besides ... just think about it for a second. There are thousands of
> tower installations with a tower base buried in the concrete. What
> would be the difference, other than beneficial spreading of the
> current, if the tower was also properly connected to the rebar cage?
Mine has taken at least 17 direct hits and there's not even a chip in the
concrete. It was getting to be a regular thing, but nary a strike (that any
one has seen) in the last 3 years. This will be the 4th summer. Who knows
what it will bring.
> Lastly, connecting the tower to the rebar cage is REQUIRED by most
> zoning regulations.
>
> I'm honestly curious why certain urban legends, like this one, seem to
> have such staying power in ham radio.
Probably because those who have seen it were so impressed they let the
rarity of the event outweigh the effectiveness of the procedure.
73
Roger (K8RI)
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