> Lightning can’t tell whether something is grounded
> because the energy pulse hasn’t gotten that far yet.
[Full bottom quote follows reply.]
The path for lightning is determined before the main pulse of energy
loss happens, and much of the communication involved in determining the
path happens at the speed of light.
The actual lightning flash is a wave of energy conversion, from
electrostatic, to heat (and then to sound and light). The energy to
drive it is already there. It is isn't travelling down the growing
bolt, but rather being taken from the volume surrounding it.
In fact, the main energy conversion doesn't happen until after the
complete initial path has been established and actually propagates upwards.
Where it happens will be influenced by the distance between grounded
conductors and the cloud, so, at the early stages, the presence of
grounds (although not necessarily particularly good ones) will have an
impact. However, it will also depend on the degree of corona discharge,
which will depend on the sharpness of objects, as corona discharges
will, effectively extend the effect of the ground into the air above the
point.
The whole process will be complicated, and there will be a significant
random element, but the presence of grounded conductors will have an
effect in the very early stages.
--
David Woolley
On 28/07/2023 22:46, Walter Underwood wrote:
Lightning can’t tell whether something is grounded because the energy pulse
hasn’t gotten that far yet.
Lightning induces a current in every nearby conductor. When that pulse of
current reaches a building or electronics, we want to provide a low impedance
path to a safe sink (ground rods) and a high impedance path to the equipment (a
choke). A lightning arrestor is a temporary low impedance path to ground for
conductors that aren’t normally grounded.
The best high impedance path is disconnecting your equipment. That won’t stop a
direct strike, because that will induce currents in the disconnected equipment.
But it will help almost all the time.
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