For 60' you won't need 6-8 people, just run a rope from the roof to about
50' up the tower and probably 2 or 3 people on the roof could pull it up.
You will need ropes on it from the ground to keep it from swinging sideways
though, just light tag lines and tell the people holding them to keep them
relatively slack or they will be fighting the roof crew.
There is no need for an air gap around the ground rods. Any air gap would
be instantly ionized from a lightning strike anyway.
David Robbins K1TTT
e-mail: mailto:k1ttt@arrl.net
web: http://wiki.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://k1ttt.net
-----Original Message-----
From: Kipton Moravec [mailto:kip@kdream.com]
Sent: Friday, March 16, 2012 19:20
To: towertalk@contesting.com
Subject: [TowerTalk] Looking for a sanity check on a tower install
I am supervising the installation of a 60 foot Rohn 25 tower. (This means
finding the people with knowledge and muscle.)
It will be placed next to a 50 foot building with concrete walls, a flat
roof, and a 5 foot parapet (wall) around the roof. (Top of the parapet is 50
feet above the ground.)
It will have one wall bracket for each section of Rohn 25 along the wall. I
know this is probably overkill, but that is what they want, and they have
the money for it.
The proposed plan is to bolt a tilt-over base to the large 6" concrete
driveway/parking lot by using butterfly expanders.
Then they want to assemble it on the ground, and tie a couple of ropes to it
at 50 ft and have 6-8 people pull it up from the flat roof. (With the same
number on the ground to help get it started.)
First question is this a good plan?
Do we need to also pull from the middle (25 feet) so there is not a bow?
Second part. The ground is all 6" concrete driveway. They are worried that
we can not just drill a 5/8" or 3/4" hole through the concrete and put
ground rods in because we have to have a certain amount of air gap between
the ground rod and the concrete, or the concrete will explode when lightning
hits.
That does not sound right to me, because the even though concrete is
somewhat conductive, the ground rod is going 10 feet into the earth. And if
I have three ground rods the lightning will be spread into the ground and
not as much through the concrete and the unknown places of rebar in the
concrete. And we already have the tilt over plate bolted to the concrete
driveway. So it is not like there is a point connection to the concrete.
Do we really need an large air gap between the ground rods and the concrete
driveway? If so how much?
Kip
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