Remember, a lightning strike a mile away can induce as much as a
thousand volts per meter in a conductor. It doesn't necessarily need a
physical connection to the strike.
I would add that the pulse from a nearby lightning strike propagates
through a building at speeds different than the induced voltages in the
wiring, let alone the wiring from different sources so it's possible, or
even quite likely to have voltage differentials in the thousands of
volts between ends of the house, or even adjacent wires in the same room
with many thousands of joules capable of starting fires, let alone
frying delicate electronic equipment.
It's different for every home and every strike. Even the magnetic fields
can induce voltages that are lethal to equipment and sometimes, humans.
Any conductor can turn into something carrying lethal voltages.
My one rig used for weather watching/nets is well protected, but I still
set it up for locked cross band repeat so the only thing I'm touching is
the HT.
73
Roger (K8RI)
On 7/25/2016 Monday 5:32 PM, Jim Brown wrote:
On Mon,7/25/2016 5:51 AM, jimlux wrote:
What you want is everything that is "near" each other connected with
good conductors that are similar in length (so the inductance is
similar, and the voltage rise from the pulse is similar).
If you have one piece of gear with a 10 foot cable to the lightning
impulse. And another piece of gear on the bench connected with a 100
foot cable to the lightning impulse, and then you interconnect the
two with a short jumper, you can see that there might be a problem.
The problem with this (and any) analysis of a lightning event is that
it is FAR more complicated than anything we can compute, simply
because the voltages and currents induced in any system (stuff wired
together) will be different in each conductor depending on WHERE the
strike is, the physical geometry of the conductors that make up that
system, how energy from the strike gets to the earth, etc.
Remember that in any given lightning event, voltages/currents are
likely to couple into our system (our home) via the power system, via
the CATV system, via the telephone system, via our antennas, and
directly onto all the wiring within our home. Voltages/currents will
be very different between those multiple systems by virtue of THEIR
geometry, how they are earthed and bonded, and THEIR proximity to the
strike.
73, Jim K9YC
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73
Roger (K8RI)
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