Jim McDonald wrote:
> My questions really were about repairing the tower, but I welcome any
> suggestions on improving the grounding.
Quite a horror story. It seems you did a lot of smart things with the
installation, but they weren't enough. I'm no lightning expert but here
are some thoughts:
An earlier post (which I can't find) referred to a consulting/lightning
protection company that strongly advocates deep drilled (at least 3 rods
to 30 feet plus) ground rods for tower strike protection. From your
descriptions of the damage, it seems to me that the strike current went
everywhere to find ground, indicating the existing radials and ground
rods (surprisingly) had too high a ground resistance/impedance and/or
too much current per radial (e.g. the blown rod connection at the end of
Here is another appropriate reference
Interesting take aways for me were the number and length of radials,
current division, potential rise, conductive cement for rods, and as
much transformer and optical isolation as is possible. So more radials
and rods for the tower or deep drilled rods and conductive cement seem
appropriate. With some googling I found some suppliers of ground rod
enhancing materials, www.ERIinc.com www.erico.com
I don't understand how a single point ground system can be made to work
globally in the average residence but it does make sense to me that
radios and PCs with peripherals have local single point grounds to
minimize the differential ground potentials they experience. I also
speculate that circuits that require DC ground connections to tower
circuits would benefit from as much series inductance as they can
tolerate. RFI filters with inductance in the ground lead to the tower
side may be an easy way to provide some ground impedance and energy
Getting rid of the conductive conduit and the common grounding radial
from tower to house/barn seems to me to be a good move as they may take
too much of the strike current where you don't want it to go.
Lightning isn't much of a problem at my current QTH. However, I'm
considering a new QTH, new tower, so all this investigation has some
value for me. Pass on any insights you gain.
My first boss had some "Engineering Maxims" that are appropriate:
There is no such thing as ground.
Capacitors turn voltage spikes into current spikes.
Every picofarad has a little nanohenry all its own. (my favorite)
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