[TowerTalk] Fwd: Looking for a sanity check on a tower install

[Hans Hammarquist]

Why on earth does anyone want a tower, with all the expence when it onl stick up 5 feet over the adjacant building? Well, that's not really my business.

Regarding lightning protection: I believe you don't have to worry about flash-over where the grounding rods go through the concrete. Fill the gap with some concrete-lika material with some conductivity and you have a very good ground. You should do that in any event to avoid water prenetation. You also should worry more about lightning strikes affecting the rest of the building at each wall bracket.

My best bet is that you carefully ground the tower to the parapet. (I assume it has some metal parts that should be grounded in the building anyhow. Maybe I am wrong.)

I know one thing though, this tower will never come down from wind.

 73 de,

Hans -  N2JFS



-----Original Message-----
From: Kipton Moravec <kip at kdream.com>
To: towertalk <towertalk at contesting.com>
Sent: Fri, Mar 16, 2012 3:20 pm
Subject: [TowerTalk] Looking for a sanity check on a tower install


I am supervising the installation of a 60 foot Rohn 25 tower. (This
eans finding the people with knowledge and muscle.)
It will be placed next to a 50 foot building with concrete walls, a flat
oof, and a 5 foot parapet (wall) around the roof. (Top of the parapet
s 50 feet above the ground.) 
It will have one wall bracket for each section of Rohn 25 along the
all. I know this is probably overkill, but that is what they want, and
hey have the money for it.
The proposed plan is to bolt a tilt-over base to the large 6" concrete
riveway/parking lot by using butterfly expanders. 
Then they want to assemble it on the ground, and tie a couple of ropes
o it at 50 ft and have 6-8 people pull it up from the flat roof. (With
he same number on the ground to help get it started.) 
First question is this a good plan?
o we need to also pull from the middle (25 feet) so there is not a
ow? 


econd part. The ground is all 6" concrete driveway. They are worried
hat we can not just drill a 5/8" or 3/4" hole through the concrete and
ut ground rods in because we have to have a certain amount of air gap
etween the ground rod and the concrete, or the concrete will explode
hen lightning hits. 
That does not sound right to me, because the even though concrete is
omewhat conductive, the ground rod is going 10 feet into the earth. And
f I have three ground rods the lightning will be spread into the ground
nd not as much through the concrete and the unknown places of rebar in
he concrete. And we already have the tilt over plate bolted to the
oncrete driveway. So it is not like there is a point connection to the
oncrete. 
Do we really need an large air gap between the ground rods and the
oncrete driveway? If so how much?
Kip

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