Scott Bullock KA1CLX <email@example.com> wrote:
>Tonite was spent installing the lower rebar mat, that's all done and
>tied-anyone that does this, invest in the twirley tool for the ties-saves
>mucho work and ur wrists. Also got the verticals put in with the 1/2"
>bracing to hold it up, and then put the first 4 pieces of the top mat on.
As some of you may know, I am finally putting up a tower (72 ft Trylon
self-supporter, C4XL on top) -- more on that in another message, later.
KA1CLX's message about building the rebar cage interests me, of course,
since I'll be doing the same thing very shortly. He mentioned tying the
rebar together with a twirley tool, but not welding them. This is
interesting because I have in front of me two nice articles about "Ufer"
grounds (no, I won't fax them to you for free)... one is from December 1992
CQ and the other is from PolyPhaser.
Basically, in a Ufer ground system, you use either copper wires inside the
concrete tower base, or the rebar cage if you have one, as part of your
ground system. The tower is tied to the cage, and the cage is tied to a
soil ground radial/rod system.
Both articles seem to indicate definite advantages to using the "ufer"
concrete base grounding system to augment the radial (with ground rods if
possible) grounding system, if/when the tower is hit by lightning.
The CQ article by VE3OLN explains the actual Ufer installation better, and
"Cadwelding is the most effective way of achieving both a good
mechanical and electrical bond between lengths of rod. In lieu of
cadwelding, arcwelding seems to be an acceptable alternative, as long as
all rods are thoroughly welded on all sides, not just tacked. Thorough
welding will enhance electrical continuity and current-carrying capacity.
"Avoid brazing or simply tying the sections of rod together. Brazing
tends to break down in high current (and high heat) conditions and simply
tying the sections of rod together neither mechanically nor electrically
bonds the sections of rod. With a breakdown of or lack of good electrical
continuity comes arcing, and it is this arcing that can cause extremely
high heat conditions within the concrete block. This extreme heat is what
can cause extensive damage and deterioration within the concrete block or
OK... now the author is saying not only that it's a good idea, but if you
don't, it could cause damage to the concrete block!
QCAO* Future Inductee - 2004
(* Quarter Century Appliance Operator)
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