Jim Jarvis wrote:
> The idea is to provide a low impedance path AROUND the concrete
> for lightning to get to ground, not THROUGH it.
Why? If it is indeed a low impedance path (and it would be useless if
it wasn't), why is it less desirable to run it through the concrete than
> Personally, I would not attach the rebar to the tower at all. To do
> so only makes
> that a more viable path for lightning.
Why? The tower legs (or the tower base or the tower mounting bolts) are
already embedded far into the concrete and they arguably form the lowest
possible impedance path INTO the concrete. Besides, Polyphaser strongly
recommends making a Ufer ground out of the rebar cage specifically for
the purpose of lightning protection (see http://tinyurl.com/4grr2o). In
fact, my local zoning department INSISTED that the tower be bonded to
the rebar cage.
> In addition, the corrosion
> which will take place
> with the copper attachments will assure that in 10 years, those
> embedded connections
> can't be trusted.
That's why Cadweld connections should be used to bond to the rebar, and
it isn't any more difficult to do that than to bond the ground wires to
ground stakes. I bought the mold and materials to do so on eBay for
less than $30.
I keep seeing this same discussion pop up time after time, and yet I've
never seen a single coherent, fact-based argument why a ground wire
should not be run through a concrete tower base. Lots of people claim
to have heard about a tower base that exploded for that reason, but even
Polyphaser says they haven't been able to confirm any instance of it
(they call it a myth). I installed a tower and antenna system at my own
QTH over the last few months --- I bonded the tower base to the rebar
cage and ran six ground wires from the tower out through the side of the
concrete base to be connected to ground rods in a radial pattern.
Pictures of the entire installation can be found at
http://tinyurl.com/5jj8gy. We get some major lightning storms here in
southern Arizona during our summer "monsoon" season and if my concrete
explodes I'll be sure to let everyone know and add pictures of it to the
web site, but in the meantime it would be nice to see this discussion
revolve around facts instead of urban legends.
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