Re: Won't strike twice.
- From: "H. Seldon" <hseldon0@xxxxxxxxx>
- Date: Mon, 12 Jun 2006 10:09:35 -0200
On Sun, 11 Jun 2006 16:33:00 -0700, w_tom wrote:
Protection from lightning was routine 50 years ago where humans
learned basic concepts. Why does a $multi-million telephone company
computer, connected to overhead wires everywhere in town, not shutdown
for every thunderstorm?
Now there's a really practical suggestion. Bring New York to a screeching
halt because of a thunderstorm? I'm sure you'd get that one by the city
fathers, not to mention business. For god's sake man, it's a very very
complex world compared to what it was 50 years ago.
Why do commercial radio and TV broadcasters atop the Empire State Building suffer
typically 25 direct lightning strikes and continue operation
uninterrupted?
They get struck very often because of the elevation of the antenna systems
(remember, the shortest path for lightning to ground) and they continue
operating because the antennas are all at "DC" ground potential. That is
the nature of the design of TV and FM transmit antennas. Only AM antennas
are not at "DC" ground and many tens of thousands of dollars are spent on
AM systems to protect them from lightning as best as possible. These
processes don't always work either as they depend so heavily on path and
ground conductivity.
Because protection from direct lighting strikes is well understood and
routinely avoided.
Sometimes that is so, especially when the planets are properly aligned and
the moon is in the seventh house.
Since many suffer damage using grossly undersized
plug-in protectors, so we have myths about protection not possible.
Instead we consult testimony from professionals:
http://www.harvardrepeater.org/news/lightning.html
Well I assert, from personal and broadcast experience spanning 30
years, that you can design a system that will handle *direct lightning
strikes* on a routine basis.
Bullshit. If you knew your job, your degree of certainty regarding
lightning protection would not be so absolute.
It takes some planning and careful layout,
but it's not hard, nor is it overly expensive. At WXIA-TV, my other
job, we take direct lightning strikes nearly every time there's a
thunderstorm.
Of course you do.
Our downtime from such strikes is almost non-existant.
Of course it is, as was explained earlier in this response. You're in
broadcasting and you don't understand why TV and FM systems take multiple
hits and don't go off the air?? The only TV/FM transmitters I have ever
seen go down because of lightning strikes are those where the lightning
entered the transmitter system through the AC distribution system,
not the antenna. The antennas *are* at DC ground.
God help your employer if you don't have a handle on simple shit like that.
The last time we went down from a strike, it was due to a strike on the
power company's lines knocking *them* out, ... Since my disasterous
strike, I've been campaigning vigorously to educate amateurs that you
*can* avoid damage from direct strikes. The belief that there's no
protection from direct strike damage is *myth*. ... The keys to
effective lightning protection are surprisingly simple, and
surprisingly less than obvious.
Nobody said there was "no" protection just that it is certainly not
fool-proof.
Of course you *must* have a single
point ground system that eliminates all ground loops. And you must
present a low *impedance* path for the energy to go. That's most
generally a low *inductance* path rather than just a low ohm DC path.
Some pray. Others learn well proven science.
Those who understand the beast fully, realize that controlling it is part
science and part "black magic". Hence the 'finger-crossing and pray'
factor. You know, like the fudge factor called ether.
If you suffer damage, then learn where your earthing is insufficient or where wires enter the
building without first a short connection that that earthing - either by direct wire or via a
'whole house' type protector.
WTF are you trying to say??
Protection from direct lightning strikes is so routine as to be
considered human failure. If damage occurs, the human should learn from
and correct that human created mistake. Earthing is so essential to
effective transistor protection that Ufer grounds are routinely
installed in new buildings with effective protection. How did an Orange
County FL stop suffering damage from lightning? They repaired defective
earthing:
http://www.psihq.com/AllCopper.htm
Single case concerning *obviously* lousy grounding.
Protection from direct lightning strikes is routine when the human
learns about and installs effective earthing. Taht also means every
incoming utility wire in every cable should make a 'less than 10 foot'
connection to earth. A concept originally demonstrated by Ben Franklin
in 1752.
Theoretical solidity but not practically feasible in most cases.
H. Seldon wrote:
If you can find a fool-proof method of lightning protection, let me
know. Lightning is one of the least understood phenomona in the world
of electricity. Be assured however that it *will* find the shortest
path to ground no matter how much it has to destroy in order to get
there. One of the most commonly used devices used for 'non-direct'
hits is the MOV (Metal Oxide Varistor). I normally use the 130 Volt
units for computers. These serve well for voltage spikes on the AC
line.
When dealing with lightning however, the best protection I can suggest
is the crossing of the fingers and a short prayer. Just in case.
--
________________________________________________________
H. Seldon
I wish there was an "Intelligence" control on the TV set.
There's a "Brightness" control, but it doesn't work.
VectorLinux SoHo 5.1
.
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