[TowerTalk] Do I Need To Strip The Wire?

[Eric Gustafson]

Hi Dave,

See my comments in your message text below.

73, Eric  N7CL


>From: "DavidC" <eDoc@netzero.net>
>Date: Tue, 4 Jan 2000 16:04:27 -0500
>
>I am about to get the connecting wire between my ground
>rods brazed.
>
>Do I need to strip the entire length of the connecting wire
>(rods are 8 feet deep and 16 feet apart as recommended here)
>or only the points at which the wire will be brazed?

It isn't _essential_ to strip all of it.  But if the ground
conditions in the trench are good (dirt, not rocks, etc.) the
horizontal run of conductor could considerably lower the system
impedance and widen its bandwidth.  The best case is a large
surface area bare conductor buried in either good or enhanced
ground.


>
>I have been told that the rods do the real work and if the 
>lightning wishes to escape the wire before reaching the rod
>that the insulation won't matter!  ;-)

Ideally, the rods provide a damage resistant point for plasma
formation below grade.  If the earth "recruited" by the ground
system becomes saturated before the charge available to the
lightning stroke is all dissipated, the system voltage will rise.
If it rises far enough, an arc will form between some point on
the ground system and the "real" or "remaining" earth.  You
really want the attachment point on your system for that arc to
be far below grade and on something that won't melt much.  That
is what the ground rod is for.  But lower ground system fault
potentials (and potential differences if the system is properly
designed) result when the system is robust enough to sink all
the charge before the rod has to do its thing.

If the potential difference between some point on the insulated
wire and the end of the ground rod exceeds the arc formation
threshold, the insulation will indeed not be terribly
significant.  But if this condition arises it is because the
inductance of the connection to the ground rod is far too high.
It means that the system is not designed to force the plasma
formation point to be the bottom end of the ground rod.  This
would be a safety problem because you have no control of exactly
where the plasma actually does form.  So Side flashes are
probable.  Depending on what or who is located where the side
flash happens, this could be a real problem.

In your case, the wire is connecting two rods.  So as long as the
fault finds the first rod via a low inductance path, it will
become the arc (earth) terminal if required.  It is unlikely that
the potential between the interconnecting wire and the
surrounding earth would get high enough after that to form a side
flash off the interconnecting wire.


>
>I thought someone told me that impedance was an issue and
>I don't know if insulated versus non-insulated connecting wire
>impacted that meaningfully.

It might or might not depending on local earth conditions.  See
above.


>
>- Thanks! & 73, DavidC  K1YP in Hudson, FL

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