It's been said by others but is probably worth repeating here that any
ground system making use of the rebar in the foundation must have the rebar
cage welded or bolted (not sure how practical that would be... bolting
rebar?) together to prevent sparks in the slab. I don't know this for
certain, but I believe it may be the danger of an inadequate bond between
all the metal in the foundation that leads tower manufacturers to specify
that the tower base must not be connected to the rebar. Also, I have heard
from enough others that I am now fairly convinced that the "exploding"
concrete is not a myth. It probably doesn't happen very often, and it may
be more of a crack than an explosion, but it's something to avoid in any
case. I wonder if anyone has any pictures of a concrete base so damaged?
As I don't have any way to weld my rebar, and I have to thread it through
the tower base as the base and rebar go into the hole so I can't have it
welded at a shop, I've decided to obey the LXC Prime Directive and follow
the manufacturers directions, which are to not attach the tower to the
rebar. I will install the best possible ground outside of the concrete. I
have lived with an ungrounded tower for almost twenty years. It would be
ironic if now, after all this ground-exercise, I get to find out what a hit
will do.
73 - JC, K0HPS
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com]On Behalf Of Nick Pair
Sent: Thursday, July 06, 2006 12:11 PM
To: Gary Schafer; towertalk@contesting.com
Subject: Re: [TowerTalk] Grounding base slab and pier tower bases
Hi Gary,
The key words to your posting on exploding bases was the fact stated that
the base section or bolts were the ONLY ground attached to the tower.
I nor other have never stated that would be a safe application. The Ufer
rebar combination was to be used in addition to a ground grid of wires and
rods suitable for the soil conductivity of your local. You need current
carrying capacity and the lowest possible impedance for your best
protection.
Also the type and method of concrete placement has a lot to do with its
ability to resist cracking. A properly reinforced concrete base can be
cracked and still be serviceable if the engineered amount of iron was used
in cage. Cracked bases are not the norm for commercial monopole and
triangular towers and they take a lot more hits system wide than amateur
towers.
If you can't have the best, you have to make what you have work to its
ultimate potential.
73
Nick
WB7PEK
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