You save me a lot of writing. This is my thought experiment. Just another
point or two. 1) the more radials there are the lower the current in each. With
enough radials, the currents are milliamps, unless you're running the megawatts
I spoke of earlier. 2) If there are two (or more) verticals, the power divides
and there is even less current per radial.
Now consider two verticals driven in phase. The radial currents will also be in
phase and even if they cross there is no voltage difference between them so
there is no arc. You can tie them together if you like but it serves no
function other than to change the resonant frequency of the shortened radials
and upset the current distribution. Yes, they do have a resonant frequency,
they are after all open ended transmission lines.
Now consider the case where the verticals are driven out of phase. The radial
currents are also out of phase and there will a maximum voltage gradient between
them. This however, is the DESIRED condition. Short the ends together and you
upset the phasing. I have no idea how significant this is, as I said this is a
thought experiment not a thesis.
Wes N7WS
On 11/6/2020 10:43 PM, Jeff Blaine wrote:
I of course defer to Frank's expertise here. But after thinking about this
for a couple of hours, I'm trying to wrap my head around this arc risk concept
as well. It's interesting and I toss this comment out because my two sets of
4sq don't have a single cross-bonded wire anywhere - all the ground structure
is ground mounted, with overlapping wires literally all over the place. And
despite that, the do seem to work more or less OK, as far as I can tell.
I guess my thinking is list this... All those radial wires are laying out on
the ground. So they are at least connected at some point, at a DC level,
assuming your talking about something conventional like a 4SQ.
Of course, we are talking about AC here, so I will agree that maybe the
conditions could exist where - with just the right configuration between the
two radials - that some larger than expected voltage differential may be
present. Given how low Q a 4SQ is, how current is split between multiple
elements, my gut feeling is that the excitation voltages are pretty mild even
if you have your 1500W source right there at the 4SQ input.
And on top of that, the wires are laying on the ground, right? The radials are
in more or less intimate contact with the ground, so I would expect there to
exist leakage resistance between adjacent conductors (if they are bare). And
if they are perfectly insulated, this being AC, that means there is going to
be some amount of cap coupling between adjacent wires and to the ground. With
all of that R&C spread out all over the field, I would certainly think this
conspires to work against the probability that any two optimally aligned
individual crossing conductors would provide a condition sufficient to support
an arc, and that if so, it would survive long enough to cause a fire.
It's very very very dry here in the summer and again in the winter. So fire
risk is something we keep a real close eye on. Then again, out here in the
Midwest some of us do a lot of IL-advised things because they seem to work and
of course because laziness is a BIG part of the calculation. ha ha. Maybe we
have been taking a walk on the wild side without realizing it. Hope not
because I sure don't want to go try to rectify this poor decision 3 years post
installation! Say it ain't so!
73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com
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