Topband: OT - Bonding Radials at Intersections

[Wes]

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