Hi Pete,
> >You _can_ do that. But until the surface area of the ground wire
> >and coax shield are larger than the surface area of the tower
> >structure, the tower will still be carrying the majority of the
> >stroke current.
>
> Is that the case, even if the tower has electrical discontinuities such as
> section-to-section joints? I'd always understood that a lower-resistance,
> lower-impedance connection would get the lion's share of the current,
> voltage-divider fashion. Am I oversimplifying (again)?
Yes. It is easy to oversimplify lightning.
What you'd need to do is calculate the voltage gradient along the
tower, and see what the breakdown voltage of the gaps are.
Once those gaps breakdown and ionize, the resistance of them is
virtually zero compared to the rest of the impedances. You would
have heating in those gaps, but the surface are of the joints is so
large and the thermal mass so high, plus the gap is non-critical for
small surface damage and the breakdown voltage probably very
low, that the gap is virtually meaningless.
Sometimes we get lost worrying about things that are never
problems. Has anyone on this reflector EVER seen a crank-up
tower damaged by arcing at the leg joints?
This isn't a 1-1/2 volt per foot continuity problem, it is a tens of
thousands of volts per foot continuity problem. At that voltage you
could ignore that small gap in this application.
.
73, Tom W8JI
w8ji@contesting.com
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