"w_tom" wrote in message
...
Cited was an industry professional who demonstrate simple
protection even for amateur radio installations. He discussed
protection without damage for *all* radios, including
repeaters. You think effective earthing requires what
commercial broadcasters install? Yes, some so deny the power
of earthing. Very little protects radios from most direct
lightning strikes. However some will cry that such earthing
cannot protect from the rare 1%. If earthing is only 99%
effective, then no money should be spent - all earthing is
useless? Reality, effective protection from direct lightning
strikes is about simple and inexpensive earthing. Frank
Gilliland has even posted unrealistic and fictional numbers,
and then denies the power of earthing - a concept well proven
in virtually every town throughout the world.

BTW Frank, to correct your post: low *resistance* (not
impedance) ground is fine for AC line protection. A low
*impedance* ground is necessary for lightning protection. One
must know the difference to understand simple earthing
concepts - and why earthing is so effective. How can you be
so critical of earthing and not even know the most basic of
basics - impedance verse resistance?

Even basic numbers such as the typical pulse width are silly
speculation. Typical lightning strike is a classic 8/20
usec. That is microseconds - not 0.1 seconds - which is why
lightning does not have the energy content of myth.
Furthermore, 1,000,000 volts does not appear at that
lightning strike. In fact a major destructive direct strike
to the building is well defined in research papers - as to not
exceed 6,000 volts. One should first learn the science.
Basic electrical circuit theory makes it obvious why the
millions of volts up there don't appear down here. Either
those millions of volts must be up there or down here - cannot
exist in both locations. Again, first semester circuit theory
that every graduate of West Point and Annapolis has learned.
Please first learn that basic circuit theory before disputing
IEEE papers, other well proven research, and NEC requirements.

Correctly noted is that most people don't climb trees to
search for lightning damage to trees. But then researchers
such as Alan Taylor of the US Forestry Service are not just
most people. Lightning has such low energy that most every
tree directly struck has no appreciative damage. Speculate
all you want. He did the work and wrote the paper.

Using your reasoning for why earth cannot conduct the
electricity even in a badly polluted salt marsh: then
obviously lightning could never conduct miles across the sky
and obviously lightning does not strike a non conductive
earth. Why does air conduct miles of lightning that only
contains millions of volts? First learn the many stages of
how air and earth become such excellent conductors. Does a
cloud strike 5 miles diagonal to connect cloud to charges on
earth? Of course not. Lightning travels 3 miles straight
down and then 4 miles through earth to complete a circuit.
Lightning takes a more conductive path via air and earth
rather than an electrically longer 5 mile path only through
air. Conductive earth is also why earthing a direct strike
(the single point earth ground) is such effective protection
from a direct strike.

Because even simple concepts of impedance verses resistance
are not understood, then even safety grounds (third prong in
wall receptacle) are confused with earth ground. Safety
ground is different from motherboard ground is different from
chassis ground is different from automobile ground is
different from breaker box ground is different from power
plant ground is different from earth ground. Most all are
interconnected, but are still electrically different. Learn
about impedance. No earth ground is found in wall receptacles
because the wire length - and therefore impedance - of that
third prong wire is just too far from earth ground. Again,
one must first understand impedance to appreciate what world
renown experts (some quoted here) have said about earthing.

It takes but a few milliamps to kill a human. Does that
prove lightning must be a high energy event - because it too
kills? Learn how easy a human can be killed before posting
such assumptions.

Even posted is that a buried coax is protected from
lightning transients. That is ridiculous as even made bluntly
obvious in a Polyphaser application note about damage to an
improperly earthed telephone exchange; transient damage via
buried wires.

Obvious in that long reply - even basic electrical concepts
are not understood. Real world professionals and generations
of scientific experience prove basic earthing is effective
protection. Even the NEC requires OP to earth ground his
antenna also for human safety.

Basic electrical knowledge - impedance verses resistance -
was not even understood and still Frank said everyone is wrong
about earthing.


Frank Gilliland wrote:
CB radio antennas are not commercial station towers. The latter are
verticals that have a direct connection to ground and the ground
radials. Actually, an AM broadcast tower is almost a perfect
lightning rod by design because it not only shunts the lightning
directly to ground, but also distributes the power from the
strike over the whole counterpoise field. So the tower stays at a
relatively low potential even during a direct strike. And what
-does- manage to sneak onto the line has to deal with some rather
expensive protection devices. Antennas mounted seperately on towers
(FM/TV BC, cell, commercial, etc) have the same problems as any
other antenna, but those problems are usually minimized by the use
of coax. More below.

Let's start with his numbers.

Millions of volts? Yes. But same voltage does not appear
everywhere in a circuit - basic circuit theory. Those
millions of voltage are in the sky. Surge protection is about
making those millions of voltage appear elsewhere which is why
industry professionals discuss impedance. A low impedance
connection to earth means no millions of volts.

A low impedance ground is fine for AC line protection, but it
doesn't guarantee lightning protection. We have all heard that
lightning takes the shortest path to ground, but that's not really
true since electricity will take EVERY path to ground available.
Lightning creates it's own conduit from the clouds, but once
it hits a conductor on the ground it behaves just like any other
form of electricity -- almost. The fact is that wire has
resistance, and the resistance of copper increases with
temperature, which is what happens when it passes the current from
a lightning strike. When that happens it will continue it's path
to ground (assuming the wire doesn't fuse), but other paths will
share more of the load. And because there is a resistance, there
will also be a voltage potential across that resistance. If that
voltage potential is high enough it will happily arc over to
another ground path, and frequently does. More below.

Millions of amps? Only in dreams. Most lightning is below
20,000 amps and of such short duration as to not be high
energy. Lightning typically so low energy at the strike
location (not to be confused with what is miles above) that
well over 90% of all trees struck leave no indication of that
strike.

Let's take your figure of 20,000.... no, let's go even lower.
Let's say only 1000 amps @ 1,000,000 volts. And let's say this
is an unusual strike in that it only hits once, not multiple
times like a normal strike. And let's say the duration of the
hit is 1/10 of a second. This will be a pathetic bolt of
lightning to be sure! Ok, so let's do some numbers:

1,000,000 Volts x 1000 Amps = 1,000,000,000 Watts
1,000,000,000 Watts x 0.1 sec = 1,000,000 Watt/sec

One million joules is "low energy"? Get a grip.

Trees struck by lightning usually -do- leave an indication of
being struck, but most people don't climb them to search for the
point of contact, which is typically nothing more than a spot
about one or two cm in diameter that has been charred. And while
the reason trees are able to survive direct lightning strikes
is still the subject of debate, the reason they make good
lightning rods (efficiently conducting the strike to ground)
shouldn't be so suprising when you take a look at a cross-section
of the root structure -- interesting how it resembles an
electrical discharge, isn't it?

Ok, back to your low impedance ground. A ground rod is used to make
an electrical connection to the earth. But the impedance of that
connection can be anywhere from a few ohms to a few hundred ohms,
depending on the type of rod and the conditions of the soil. Let's
just say we have a ground with an unbelievable impedance of 1 ohm
(a solid-silver rod in a heavily mineralized salt-water marsh
that was recently used for dumping copper turnings from a very
poorly run machine shop).....

1000 amps x 1 ohm = 1000 volts

So with an almost impossibly good ground and a puny bolt of
lightning you -still- have 1000 volts at the top of your ground rod.
So a more typical ground impedance of 50 ohms (not coincidence) and
a more typical lightning strike of 10,000 amps will put 500,000
volts on your grounding strap.....YIKES!!!!! This is a fact, and it
certainly doesn't seem to jibe with your statement that the
voltage at the bottom is insignificant!

How big need a wire be to shunt (earth) lightning? Even the
US Army training manual TM5-690 requires 10 AWG wire to
conduct the direct lightning strike without damage.

Ever hear the term "military intelligence"?

Same wire
found in 20 or 30 amp AC electric boxes because lightning is
not the millions of amps so often claimed in urban myths.
Unlike Frank, numbers are provided by multiple, reliable
sources.

The ground wire in house wiring is intended for fault protection,
not lightning strikes. For example, if the hot wire in your
vintage all-metal Craftsman drill suddenly comes loose and shorts
to the case, since the case is grounded it will shunt the majority
of the current to ground through the ground wire, not through
the person using the drill. And if your breakers and wiring are up
to code (neutral grounded at the box), that current lasts only
for a very short time, limiting any damage to the person and the
drill. Therefore, the ground wire in your house doesn't need to be
as thick as the main wires, and it isn't. Next time you visit your
local hardware store, look at the specs on a spool of house wire --
hot and neutral may be #10 while ground will be #12. Another spool
may have a pair of #12 wires and #14 for ground. If this ground
wire was intended for lightning protection, wouldn't it all be the
same size? Fact: the NEC doesn't define ground wire size based on
it's ability (or inability) to protect against lightning.

Another who does this for a living:
From Colin Baliss "Transmission & Distribution Electrical
Engineering":
Although lightning strikes have impressive voltage and current
values (typically hundreds to thousands of kV and 10-100 kA)
the energy content of the discharge is relatively low ...

Relative to what?

or Martin A Uman in All About Lightning
Most of the energy available to the lightning is converted along
the lightning channel to thunder, heat, light, and radio waves,
leaving only a fraction available at the channel base for
immediate use or storage.

Then I guess all the people that have been killed by lightning
didn't die from the power in the lightning, did they? And all
the damage to electrical equipment caused by lightning wasn't
from the lightning at all, was it? And that pro golfer that was
knocked flat on the links by a nearby strike must have been hit
in the head with a ball at the exact same time, huh? No, no and
no.....

....

It's obvious that you have no experience in the real world
with lightning damage. Get some.

While this pains me, Frank's right. You can go on
with your babble, but there's no reasonably priced grounding
system that will protect you as good as unplugging everything
from the wall and antenna.

Landshark


--
Hard things are put in our way,
not to stop us, but to call out our
courage and strength.