At 12:48 PM -0500 9/23/97, Dick Flanagan wrote:
>Polyphaser's book suggests you bond the rebar cage to a tower leg with 2/0
>wire or strap and also bond the cage to the external ground field via
>another 2/0 wire or strap.
>
>I had two Polyphaser engineers assist me with designing my tower footing
>and that is what they suggested.
>
>The rebar cage is connected together by wire ties; no welding. The rebar
>cage has eight 2/0 pigtails attached to it. Seven pigtails extend
>horizontally below grade and connect to each ground radial. The eighth
>pigtail extends vertically through the top of the footing and is bonded to
>a tower leg. The J bolts are not bonded to the rebar.
>
>73, Dick
>Dick Flanagan W6OLD CFII Minden, Nevada (South of Reno)
Thanks, Dick!!!! I really misread the article. In the PolyPhaser Ufer
article, it states, "It stands to reason that the outer most sections of
the rebar structure should be bonded together, not just tied. If tied, a
poor connection could cause an arc. Because arc temperatures are very high
and are very localized, they could cause deterioration of the concrete
(cracking and carbonizing) in that area."
But then, they put holes in that theory in the next paragraph...
"This has NOT been the case. In fact, '...it has been found that these
wire ties are surprisingly effective electrical connections. One might
think that the ties would fail under fault conditions. However, it should
be remembered that there are a large number of these junctions effectively
in parallel, cinched tightly.' (IEEE Seminar Notes 1970.)"
So... survey says... Do a Ufer ground in addition to my other grounding
plans and don't bother to weld it. That sounds like a winner to me!
73 Scott KA9FOX
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