Aidan Grey wrote:
To all:
This statement is correct. A lightning bolt often consists of as many as
40 to 50 individual discharges. This is not apparent unless the lightning
is captured by high speed photography.
So, since the lightning discharge turns on and off 40 to 50 times in a
fraction
of a second, it is not pure DC.
The current flows in only one direction. However, the energy is split
between a DC component, and a considerable part that is effectively RF
energy. Note this is RF energy, not low frequency AC.
A small multiple of 40-50 Hz is not exactly RF. So what's the risetime
of these pulses? Duration?
I don't have a Web source to cite for this, but I have read about this
before. Specifically, that a ground for a lightning rod must not go through
a coil of wire.
Why would you want one to run through a coil, anyway?
I suspect the warning is to avoid somebody being electrocuted by induced
current from the pulse(s).
Aidan Grey
On 5 Jul 2005 06:40:58 -0700, w_tom wrote:
Effectiveness of protection from lightning is determined by how that
electricity gets to earth ground. Not earth ground beneath you. If
seeks charges via earth that is maybe miles away. In the process, the
struck batting cage then carries electricity underneath your feet to to
take a mile plus path to those distant charges.
For example, if standing on earth with feet apart, and if the nearby
tree is struck, then electricity might pass through earth, up one leg,
down the other, and then continue through earth. Therefore the human
is electrocuted.
This is also why four legged animals tend to be at risk when a nearby
tree is struck. Four legged animals do not make a single point ground
connection to earth; therefore can be harmed by electricity flowing
through the earth.
The baseball cage may act as a good lightning rod. But then
electricity passes beneath a human to cause harm. IOW the faraday cage
is not complete because the earth beneath the human was not
sufficiently conductive.
BTW, lightning is not DC. Lightning is AC current - mostly in radio
frequency ranges. This AC nature is why longer conductors, sufficient
for 60 Hz AC electric power, can be poor conductors to lightning; its
energy in higher frequencies. This AC nature of lightning is why so
many humans think lightning is capricious.
Tom MacIntyre wrote:
Hi folks...this was in a baseball newsgroup that I participate
in (rec.sport.baseball). Faraday cages have been
mentioned, implying that it could be safe. I don't
know that I'd trust this against lightning
(maybe
a Van de Graff generator). What do you think?
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