[TowerTalk] [LP/PQ] Lightning Damage Case

[K1TTT]

> 
> Unless exceptional bonding and lightning grounding establishes an equi-
> potential plane, it is possible that you will have to suppress all
> external input and even inter building wiring.  Just running grounds in
> parallel with power or signal conductors may not be able to
> reduce damaging current flow.  I have seen numerous cases of wiring in
> buried metal conduit be unequal to the task of reducing damaging energy in
> the wires.

All wires entering a building should have suppressors.  You can NOT stop the
current flow, only redirect it... preferably away from your equipment.

> 
> >From your description, the most likely problem that you encountered was a
> ground potential rise involving the pole servicing your location.
> 
> The voltage of the location where lightning enters into the soil is
> elevated substantially, together with all nearby equipment.  Despite our
> efforts, with the best ground electrodes, the resistance is almost always
> too high to avoid creating this high driving voltage. 

You can NEVER stop this voltage rise, it is part of the physics of the
lightning.  The aim of 'grounding' is to keep all equipment in the immediate
area at the same voltage.  The biggest unrecognized problem is if the stroke
hits the ground near a structure the voltage on the ground system will go up
relative to the voltage on the power/phone/catv conductors.  This causes
what is commonly called a 'backflashover' where the rapid change in the
ground voltage causes an arc 'back' to the power/signal conductor who's
voltage hasn't changed yet.  This is counterintuitive to most people since
you normally think the surges are on the power line or on the signal line,
in many cases this is not the situation.  
 

David Robbins K1TTT
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