Lightning Strike
 

I wrote:

By the way, lightning rods are not supposed to "draw the lightning"
\ away from the protected structure. Any wire you might use would be
far too flimsy to carry such a load. What a lightning rod does is
to slowly discharge the atmosphere surrounding it


"w_tom" wrote in message

This is the scam promoted by the Early Streamer Emission
industry.

Actually, this is the scam first promoted by Benjamin Franklin. Turns out he
was wrong. So was I in my previous posting, so I may well be the first
newsgroup poster in history to admit to error. Being somewhat elderly, I
tried to recall what we learned about lightning in physics class, and got it
mixed in with what we learned about Franklin in history class. It seems even
Ben realized later in his life that lightning rods do not discharge clouds,
but merely provide a safe path to ground for the lightning.

The US Army defines in TM5-690 a wire size sufficient to
discharge lightning without damage. 10 AWG. This makes
complete sense once one learns a direct lightning strike has
so little energy.

Hmmmm. It seems to me knocking bricks off of buildings, or splitting trees,
or making very loud noises and bright lights suggests more than "so little
energy". Various non commercial websites suggest that a typical lightning
strike releases 250 KWH of energy. A big one may release 10 times that much.
That is a lot of energy. Admittedly, most of that is dissipated in the air
above where it strikes, but I think it is disingenuous to characterize it as
"little". It is not a lot, for example, compared to what it takes to light
New York city. On the other hand, that amount of energy is concentrated in
less than a millisecond, so it is very intense.

notes, and are based upon decades of experience. If lightning
vaporizes wires, then Ben Franklin did not exist to sign the
Declaration of Independence.

Ben's kite did not actually get struck by lightning, but just picked up the
cloud charge. His kite string was not a copper conductor and did not conduct
a large current.

A lightning rod above the pond and properly earthed by 10
AWG or heavier wire is more than sufficient to intercept and
divert lightning to earth without pond damage.

Most lightning rod manufacturers use 2 or 0 gauge wire as the down wire. 10
gauge seems to me a little flimsy. Given that a 10 gauge copper wire has a
resistance of about 1 ohm per 1000 feet, and given a total length of wire
of about 50 feet, we are dealing with 0.05 ohms of resistance. Given also
that an average lightning strike can have a current of 10,000 amps (NASA has
measured at least one strike of 100,000 amps)(and that the conductor takes
the entire current) we are dealing with a dissipated power of 10000^2*.05
or 5 million watts. Or 100,000 watts per foot of wire. Admittedly this is
for a very short time. But I submit that 100000 watts applied to a foot of
this wire over a millisecond will melt or otherwise seriously damage that
wire.

Lightning Strike
 

Ben,

There is a lot of power in lightning. I was told that the measurement of a
10 mile long streak of lightning would power a city of 5,000 people for a
year. Be that as it may, I read about a guy that observed "ball lightning"
(I know it is not normal lightning) hit a concrete gate piling with a chain
on it that had links about 6 inches long and 4 inches wide, and was very
heavy, and it explode the piling into dust and welded all the links of chain
into a solid length of metal. He wasn't very old when this happened but the
older people said it was a good thing that he was not close because the
energy dissipated was a lot. Pictures of the chain and the pilings were in
my Weekly reader when I was in the fourth grade.

Mother Nature has a tendency to pack a punch.

Tom L.L.
---------------------------------------------
"bmuller" wrote in message
s.com...
I wrote:

By the way, lightning rods are not supposed to "draw the lightning"
\ away from the protected structure. Any wire you might use would be
far too flimsy to carry such a load. What a lightning rod does is
to slowly discharge the atmosphere surrounding it


"w_tom" wrote in message

This is the scam promoted by the Early Streamer Emission
industry.

Actually, this is the scam first promoted by Benjamin Franklin. Turns out
he
was wrong. So was I in my previous posting, so I may well be the first
newsgroup poster in history to admit to error. Being somewhat elderly, I
tried to recall what we learned about lightning in physics class, and got
it
mixed in with what we learned about Franklin in history class. It seems
even
Ben realized later in his life that lightning rods do not discharge
clouds,
but merely provide a safe path to ground for the lightning.

The US Army defines in TM5-690 a wire size sufficient to
discharge lightning without damage. 10 AWG. This makes
complete sense once one learns a direct lightning strike has
so little energy.

Hmmmm. It seems to me knocking bricks off of buildings, or splitting
trees,
or making very loud noises and bright lights suggests more than "so little
energy". Various non commercial websites suggest that a typical lightning
strike releases 250 KWH of energy. A big one may release 10 times that
much.
That is a lot of energy. Admittedly, most of that is dissipated in the air
above where it strikes, but I think it is disingenuous to characterize it
as
"little". It is not a lot, for example, compared to what it takes to light
New York city. On the other hand, that amount of energy is concentrated in
less than a millisecond, so it is very intense.

notes, and are based upon decades of experience. If lightning
vaporizes wires, then Ben Franklin did not exist to sign the
Declaration of Independence.

Ben's kite did not actually get struck by lightning, but just picked up
the
cloud charge. His kite string was not a copper conductor and did not
conduct
a large current.

A lightning rod above the pond and properly earthed by 10
AWG or heavier wire is more than sufficient to intercept and
divert lightning to earth without pond damage.

Most lightning rod manufacturers use 2 or 0 gauge wire as the down wire.
10
gauge seems to me a little flimsy. Given that a 10 gauge copper wire has a
resistance of about 1 ohm per 1000 feet, and given a total length of wire
of about 50 feet, we are dealing with 0.05 ohms of resistance. Given also
that an average lightning strike can have a current of 10,000 amps (NASA
has
measured at least one strike of 100,000 amps)(and that the conductor takes
the entire current) we are dealing with a dissipated power of 10000^2*.05
or 5 million watts. Or 100,000 watts per foot of wire. Admittedly this is
for a very short time. But I submit that 100000 watts applied to a foot of
this wire over a millisecond will melt or otherwise seriously damage that
wire.

Lightning Strike
 

Ben,

There is a lot of power in lightning. I was told that the measurement of a
10 mile long streak of lightning would power a city of 5,000 people for a
year. Be that as it may, I read about a guy that observed "ball lightning"
(I know it is not normal lightning) hit a concrete gate piling with a chain
on it that had links about 6 inches long and 4 inches wide, and was very
heavy, and it explode the piling into dust and welded all the links of chain
into a solid length of metal. He wasn't very old when this happened but the
older people said it was a good thing that he was not close because the
energy dissipated was a lot. Pictures of the chain and the pilings were in
my Weekly reader when I was in the fourth grade.

Mother Nature has a tendency to pack a punch.

Tom L.L.
---------------------------------------------
"bmuller" wrote in message
s.com...
I wrote:

By the way, lightning rods are not supposed to "draw the lightning"
\ away from the protected structure. Any wire you might use would be
far too flimsy to carry such a load. What a lightning rod does is
to slowly discharge the atmosphere surrounding it


"w_tom" wrote in message

This is the scam promoted by the Early Streamer Emission
industry.

Actually, this is the scam first promoted by Benjamin Franklin. Turns out
he
was wrong. So was I in my previous posting, so I may well be the first
newsgroup poster in history to admit to error. Being somewhat elderly, I
tried to recall what we learned about lightning in physics class, and got
it
mixed in with what we learned about Franklin in history class. It seems
even
Ben realized later in his life that lightning rods do not discharge
clouds,
but merely provide a safe path to ground for the lightning.

The US Army defines in TM5-690 a wire size sufficient to
discharge lightning without damage. 10 AWG. This makes
complete sense once one learns a direct lightning strike has
so little energy.

Hmmmm. It seems to me knocking bricks off of buildings, or splitting
trees,
or making very loud noises and bright lights suggests more than "so little
energy". Various non commercial websites suggest that a typical lightning
strike releases 250 KWH of energy. A big one may release 10 times that
much.
That is a lot of energy. Admittedly, most of that is dissipated in the air
above where it strikes, but I think it is disingenuous to characterize it
as
"little". It is not a lot, for example, compared to what it takes to light
New York city. On the other hand, that amount of energy is concentrated in
less than a millisecond, so it is very intense.

notes, and are based upon decades of experience. If lightning
vaporizes wires, then Ben Franklin did not exist to sign the
Declaration of Independence.

Ben's kite did not actually get struck by lightning, but just picked up
the
cloud charge. His kite string was not a copper conductor and did not
conduct
a large current.

A lightning rod above the pond and properly earthed by 10
AWG or heavier wire is more than sufficient to intercept and
divert lightning to earth without pond damage.

Most lightning rod manufacturers use 2 or 0 gauge wire as the down wire.
10
gauge seems to me a little flimsy. Given that a 10 gauge copper wire has a
resistance of about 1 ohm per 1000 feet, and given a total length of wire
of about 50 feet, we are dealing with 0.05 ohms of resistance. Given also
that an average lightning strike can have a current of 10,000 amps (NASA
has
measured at least one strike of 100,000 amps)(and that the conductor takes
the entire current) we are dealing with a dissipated power of 10000^2*.05
or 5 million watts. Or 100,000 watts per foot of wire. Admittedly this is
for a very short time. But I submit that 100000 watts applied to a foot of
this wire over a millisecond will melt or otherwise seriously damage that
wire.

Lightning Strike
 

Let's review where all that energy was applied and how much
- with numbers so that we don't do what junk scientists must
do.

Don Kelly in Newsgroup sci.physics.electromag on 4 Nov 2000
entitled "Oddball question":
In a large storm, there is an appreciable amount of energy but
most of this is dissipated as heat and light in multiple strokes
over the duration of the storm (and a wide area) ... A typical
stroke will reach its peak in about 1-2 microseconds and die to
about half peak in 50-100 microseconds. Millionths of seconds,
not seconds! There may be several strokes in the same path but
even 3-5 strokes will take less than 1/1000 second. The strokes
just appear to last seconds.
Yes there is a high peak power in a stroke but this does not
translate into appreciable energy (about 55 KWH (200MJ)for an
average stroke). Energy is what we need, not high peak power.
Allowing an extremely (ridiculously so) optimistic 50% energy
recovery and noting that a high isokeraunic level may be 8-10
strokes/square Km /year- this translates to about 220-275 KWH/
sq Km/year.
A 25 watt bulb running for the full year will require
220KWH/year so a storm could supply one 25 watt bulb /sq Km/year.
How much time and effort should be spent on this miniscule
return?
Yes, a stroke can cause a lot of destruction- that is because
the energy is dissipated in a small area in an extremely short
period of time- say 40,000A for 100microseconds, into 20 ohms
resistance- 32,000,000KW but less than 1 KWH. Lots of power
but little energy.


Tom La Bron wrote:
Ben,
There is a lot of power in lightning. I was told that the measurement of a
10 mile long streak of lightning would power a city of 5,000 people for a
year. Be that as it may, I read about a guy that observed "ball lightning"
(I know it is not normal lightning) hit a concrete gate piling with a chain
on it that had links about 6 inches long and 4 inches wide, and was very
heavy, and it explode the piling into dust and welded all the links of chain
into a solid length of metal. He wasn't very old when this happened but the
older people said it was a good thing that he was not close because the
energy dissipated was a lot. Pictures of the chain and the pilings were in
my Weekly reader when I was in the fourth grade.

Mother Nature has a tendency to pack a punch.

Tom L.L.
---------------------------------------------
"bmuller" wrote in message
s.com...
I wrote:

By the way, lightning rods are not supposed to "draw the lightning"
\ away from the protected structure. Any wire you might use would be
far too flimsy to carry such a load. What a lightning rod does is
to slowly discharge the atmosphere surrounding it


"w_tom" wrote in message

This is the scam promoted by the Early Streamer Emission
industry.

Actually, this is the scam first promoted by Benjamin Franklin. Turns out
he
was wrong. So was I in my previous posting, so I may well be the first
newsgroup poster in history to admit to error. Being somewhat elderly, I
tried to recall what we learned about lightning in physics class, and got
it
mixed in with what we learned about Franklin in history class. It seems
even
Ben realized later in his life that lightning rods do not discharge
clouds,
but merely provide a safe path to ground for the lightning.

The US Army defines in TM5-690 a wire size sufficient to
discharge lightning without damage. 10 AWG. This makes
complete sense once one learns a direct lightning strike has
so little energy.

Hmmmm. It seems to me knocking bricks off of buildings, or splitting
trees,
or making very loud noises and bright lights suggests more than "so little
energy". Various non commercial websites suggest that a typical lightning
strike releases 250 KWH of energy. A big one may release 10 times that
much.
That is a lot of energy. Admittedly, most of that is dissipated in the air
above where it strikes, but I think it is disingenuous to characterize it
as
"little". It is not a lot, for example, compared to what it takes to light
New York city. On the other hand, that amount of energy is concentrated in
less than a millisecond, so it is very intense.

notes, and are based upon decades of experience. If lightning
vaporizes wires, then Ben Franklin did not exist to sign the
Declaration of Independence.

Ben's kite did not actually get struck by lightning, but just picked up
the
cloud charge. His kite string was not a copper conductor and did not
conduct
a large current.

A lightning rod above the pond and properly earthed by 10
AWG or heavier wire is more than sufficient to intercept and
divert lightning to earth without pond damage.

Most lightning rod manufacturers use 2 or 0 gauge wire as the down wire.
10
gauge seems to me a little flimsy. Given that a 10 gauge copper wire has a
resistance of about 1 ohm per 1000 feet, and given a total length of wire
of about 50 feet, we are dealing with 0.05 ohms of resistance. Given also
that an average lightning strike can have a current of 10,000 amps (NASA
has
measured at least one strike of 100,000 amps)(and that the conductor takes
the entire current) we are dealing with a dissipated power of 10000^2*.05
or 5 million watts. Or 100,000 watts per foot of wire. Admittedly this is
for a very short time. But I submit that 100000 watts applied to a foot of
this wire over a millisecond will melt or otherwise seriously damage that
wire.

Lightning Strike
 

Let's review where all that energy was applied and how much
- with numbers so that we don't do what junk scientists must
do.

Don Kelly in Newsgroup sci.physics.electromag on 4 Nov 2000
entitled "Oddball question":
In a large storm, there is an appreciable amount of energy but
most of this is dissipated as heat and light in multiple strokes
over the duration of the storm (and a wide area) ... A typical
stroke will reach its peak in about 1-2 microseconds and die to
about half peak in 50-100 microseconds. Millionths of seconds,
not seconds! There may be several strokes in the same path but
even 3-5 strokes will take less than 1/1000 second. The strokes
just appear to last seconds.
Yes there is a high peak power in a stroke but this does not
translate into appreciable energy (about 55 KWH (200MJ)for an
average stroke). Energy is what we need, not high peak power.
Allowing an extremely (ridiculously so) optimistic 50% energy
recovery and noting that a high isokeraunic level may be 8-10
strokes/square Km /year- this translates to about 220-275 KWH/
sq Km/year.
A 25 watt bulb running for the full year will require
220KWH/year so a storm could supply one 25 watt bulb /sq Km/year.
How much time and effort should be spent on this miniscule
return?
Yes, a stroke can cause a lot of destruction- that is because
the energy is dissipated in a small area in an extremely short
period of time- say 40,000A for 100microseconds, into 20 ohms
resistance- 32,000,000KW but less than 1 KWH. Lots of power
but little energy.


Tom La Bron wrote:
Ben,
There is a lot of power in lightning. I was told that the measurement of a
10 mile long streak of lightning would power a city of 5,000 people for a
year. Be that as it may, I read about a guy that observed "ball lightning"
(I know it is not normal lightning) hit a concrete gate piling with a chain
on it that had links about 6 inches long and 4 inches wide, and was very
heavy, and it explode the piling into dust and welded all the links of chain
into a solid length of metal. He wasn't very old when this happened but the
older people said it was a good thing that he was not close because the
energy dissipated was a lot. Pictures of the chain and the pilings were in
my Weekly reader when I was in the fourth grade.

Mother Nature has a tendency to pack a punch.

Tom L.L.
---------------------------------------------
"bmuller" wrote in message
s.com...
I wrote:

By the way, lightning rods are not supposed to "draw the lightning"
\ away from the protected structure. Any wire you might use would be
far too flimsy to carry such a load. What a lightning rod does is
to slowly discharge the atmosphere surrounding it


"w_tom" wrote in message

This is the scam promoted by the Early Streamer Emission
industry.

Actually, this is the scam first promoted by Benjamin Franklin. Turns out
he
was wrong. So was I in my previous posting, so I may well be the first
newsgroup poster in history to admit to error. Being somewhat elderly, I
tried to recall what we learned about lightning in physics class, and got
it
mixed in with what we learned about Franklin in history class. It seems
even
Ben realized later in his life that lightning rods do not discharge
clouds,
but merely provide a safe path to ground for the lightning.

The US Army defines in TM5-690 a wire size sufficient to
discharge lightning without damage. 10 AWG. This makes
complete sense once one learns a direct lightning strike has
so little energy.

Hmmmm. It seems to me knocking bricks off of buildings, or splitting
trees,
or making very loud noises and bright lights suggests more than "so little
energy". Various non commercial websites suggest that a typical lightning
strike releases 250 KWH of energy. A big one may release 10 times that
much.
That is a lot of energy. Admittedly, most of that is dissipated in the air
above where it strikes, but I think it is disingenuous to characterize it
as
"little". It is not a lot, for example, compared to what it takes to light
New York city. On the other hand, that amount of energy is concentrated in
less than a millisecond, so it is very intense.

notes, and are based upon decades of experience. If lightning
vaporizes wires, then Ben Franklin did not exist to sign the
Declaration of Independence.

Ben's kite did not actually get struck by lightning, but just picked up
the
cloud charge. His kite string was not a copper conductor and did not
conduct
a large current.

A lightning rod above the pond and properly earthed by 10
AWG or heavier wire is more than sufficient to intercept and
divert lightning to earth without pond damage.

Most lightning rod manufacturers use 2 or 0 gauge wire as the down wire.
10
gauge seems to me a little flimsy. Given that a 10 gauge copper wire has a
resistance of about 1 ohm per 1000 feet, and given a total length of wire
of about 50 feet, we are dealing with 0.05 ohms of resistance. Given also
that an average lightning strike can have a current of 10,000 amps (NASA
has
measured at least one strike of 100,000 amps)(and that the conductor takes
the entire current) we are dealing with a dissipated power of 10000^2*.05
or 5 million watts. Or 100,000 watts per foot of wire. Admittedly this is
for a very short time. But I submit that 100000 watts applied to a foot of
this wire over a millisecond will melt or otherwise seriously damage that
wire.

Lightning Strike
 

On Sun, 27 Jul 2003, w_tom wrote:

Let's review where all that energy was applied and how much
- with numbers so that we don't do what junk scientists must
do.

Don Kelly in Newsgroup sci.physics.electromag on 4 Nov 2000
entitled "Oddball question":
over the duration of the storm (and a wide area) ... A typical
stroke will reach its peak in about 1-2 microseconds and die to
about half peak in 50-100 microseconds. Millionths of seconds,
not seconds! There may be several strokes in the same path but
even 3-5 strokes will take less than 1/1000 second. The strokes
just appear to last seconds.
Yes there is a high peak power in a stroke but this does not
translate into appreciable energy (about 55 KWH (200MJ)for an
average stroke). Energy is what we need, not high peak power.

Which, for "Gee Whiz!" value, works out to on the order of 2x10^12 Watts
over 100 uS...

The US Army defines in TM5-690 a wire size sufficient to
discharge lightning without damage. 10 AWG. This makes
complete sense once one learns a direct lightning strike has
so little energy.

Various non commercial websites suggest that a typical lightning
strike releases 250 KWH of energy. A big one may release 10 times that
much. That is a lot of energy. Admittedly, most of that is dissipated in the air
above where it strikes, but I think it is disingenuous to characterize it
as "little".

A lightning rod above the pond and properly earthed by 10
AWG or heavier wire is more than sufficient to intercept and
divert lightning to earth without pond damage.

Most lightning rod manufacturers use 2 or 0 gauge wire as the down wire.
10 gauge seems to me a little flimsy. Given that a 10 gauge copper wire has a
resistance of about 1 ohm per 1000 feet, and given a total length of wire
of about 50 feet, we are dealing with 0.05 ohms of resistance. Given also
that an average lightning strike can have a current of 10,000 amps (NASA
has measured at least one strike of 100,000 amps)(and that the conductor takes
the entire current) we are dealing with a dissipated power of 10000^2*.05
or 5 million watts. Or 100,000 watts per foot of wire. Admittedly this is
for a very short time. But I submit that 100000 watts applied to a foot of
this wire over a millisecond will melt or otherwise seriously damage that
wire.

In addition to the DC resistance, you need to take into account the
inductance of the grounding wire. In the far more limited world of
industrial high energy discharges, an associate observed multiple
instances where a large laser flashlamp power supply was dumped to the
solid copper lab grounding grid. The cable from the crowbar switch to the
grid was about 4 feet long, running perhaps 30 degrees off the vertical.
They would see sparks "shortcut" from 18 inches or more up the cable, to
the floor, rather than continue down the direct path. What's the dry air
breakdown voltage for 18 inches? These *potentials*, with significant
energy behind them, do occur, even with properly grounded equipment!

Dave

Lightning Strike
 

On Sun, 27 Jul 2003, w_tom wrote:

Let's review where all that energy was applied and how much
- with numbers so that we don't do what junk scientists must
do.

Don Kelly in Newsgroup sci.physics.electromag on 4 Nov 2000
entitled "Oddball question":
over the duration of the storm (and a wide area) ... A typical
stroke will reach its peak in about 1-2 microseconds and die to
about half peak in 50-100 microseconds. Millionths of seconds,
not seconds! There may be several strokes in the same path but
even 3-5 strokes will take less than 1/1000 second. The strokes
just appear to last seconds.
Yes there is a high peak power in a stroke but this does not
translate into appreciable energy (about 55 KWH (200MJ)for an
average stroke). Energy is what we need, not high peak power.

Which, for "Gee Whiz!" value, works out to on the order of 2x10^12 Watts
over 100 uS...

The US Army defines in TM5-690 a wire size sufficient to
discharge lightning without damage. 10 AWG. This makes
complete sense once one learns a direct lightning strike has
so little energy.

Various non commercial websites suggest that a typical lightning
strike releases 250 KWH of energy. A big one may release 10 times that
much. That is a lot of energy. Admittedly, most of that is dissipated in the air
above where it strikes, but I think it is disingenuous to characterize it
as "little".

A lightning rod above the pond and properly earthed by 10
AWG or heavier wire is more than sufficient to intercept and
divert lightning to earth without pond damage.

Most lightning rod manufacturers use 2 or 0 gauge wire as the down wire.
10 gauge seems to me a little flimsy. Given that a 10 gauge copper wire has a
resistance of about 1 ohm per 1000 feet, and given a total length of wire
of about 50 feet, we are dealing with 0.05 ohms of resistance. Given also
that an average lightning strike can have a current of 10,000 amps (NASA
has measured at least one strike of 100,000 amps)(and that the conductor takes
the entire current) we are dealing with a dissipated power of 10000^2*.05
or 5 million watts. Or 100,000 watts per foot of wire. Admittedly this is
for a very short time. But I submit that 100000 watts applied to a foot of
this wire over a millisecond will melt or otherwise seriously damage that
wire.

In addition to the DC resistance, you need to take into account the
inductance of the grounding wire. In the far more limited world of
industrial high energy discharges, an associate observed multiple
instances where a large laser flashlamp power supply was dumped to the
solid copper lab grounding grid. The cable from the crowbar switch to the
grid was about 4 feet long, running perhaps 30 degrees off the vertical.
They would see sparks "shortcut" from 18 inches or more up the cable, to
the floor, rather than continue down the direct path. What's the dry air
breakdown voltage for 18 inches? These *potentials*, with significant
energy behind them, do occur, even with properly grounded equipment!

Dave

Lightning Strike OT? WTH brought this on?
 

So I read this thread with great anticipation of seeing how it relates to
the subject of this newsgroup! Let's all collectively compliment all these
snooty astro-phycists on their deep knowledge and ask them to go back into
their laboratory so that we can continue to enjoy our hobby!

Just my 2 cents.

--
_______________________________________
"The difference between 'involvement' and 'commitment' is
like an eggs-and-ham breakfast:
The chicken was 'involved' - the pig was 'committed'."

http://community.webshots.com/user/godwino

"Dave Bell" wrote in message
...
On Sun, 27 Jul 2003, w_tom wrote:

Let's review where all that energy was applied and how much
- with numbers so that we don't do what junk scientists must
do.

Don Kelly in Newsgroup sci.physics.electromag on 4 Nov 2000
entitled "Oddball question":
over the duration of the storm (and a wide area) ... A typical
stroke will reach its peak in about 1-2 microseconds and die to
about half peak in 50-100 microseconds. Millionths of seconds,
not seconds! There may be several strokes in the same path but
even 3-5 strokes will take less than 1/1000 second. The strokes
just appear to last seconds.
Yes there is a high peak power in a stroke but this does not
translate into appreciable energy (about 55 KWH (200MJ)for an
average stroke). Energy is what we need, not high peak power.

Which, for "Gee Whiz!" value, works out to on the order of 2x10^12 Watts
over 100 uS...

The US Army defines in TM5-690 a wire size sufficient to
discharge lightning without damage. 10 AWG. This makes
complete sense once one learns a direct lightning strike has
so little energy.

Various non commercial websites suggest that a typical lightning
strike releases 250 KWH of energy. A big one may release 10 times
that
much. That is a lot of energy. Admittedly, most of that is
dissipated in the air
above where it strikes, but I think it is disingenuous to
characterize it
as "little".

A lightning rod above the pond and properly earthed by 10
AWG or heavier wire is more than sufficient to intercept and
divert lightning to earth without pond damage.

Most lightning rod manufacturers use 2 or 0 gauge wire as the down
wire.
10 gauge seems to me a little flimsy. Given that a 10 gauge copper
wire has a
resistance of about 1 ohm per 1000 feet, and given a total length
of wire
of about 50 feet, we are dealing with 0.05 ohms of resistance.
Given also
that an average lightning strike can have a current of 10,000 amps
(NASA
has measured at least one strike of 100,000 amps)(and that the
conductor takes
the entire current) we are dealing with a dissipated power of
10000^2*.05
or 5 million watts. Or 100,000 watts per foot of wire. Admittedly
this is
for a very short time. But I submit that 100000 watts applied to a
foot of
this wire over a millisecond will melt or otherwise seriously damage
that
wire.

In addition to the DC resistance, you need to take into account the
inductance of the grounding wire. In the far more limited world of
industrial high energy discharges, an associate observed multiple
instances where a large laser flashlamp power supply was dumped to the
solid copper lab grounding grid. The cable from the crowbar switch to the
grid was about 4 feet long, running perhaps 30 degrees off the vertical.
They would see sparks "shortcut" from 18 inches or more up the cable, to
the floor, rather than continue down the direct path. What's the dry air
breakdown voltage for 18 inches? These *potentials*, with significant
energy behind them, do occur, even with properly grounded equipment!

Dave

Lightning Strike OT? WTH brought this on?
 

So I read this thread with great anticipation of seeing how it relates to
the subject of this newsgroup! Let's all collectively compliment all these
snooty astro-phycists on their deep knowledge and ask them to go back into
their laboratory so that we can continue to enjoy our hobby!

Just my 2 cents.

--
_______________________________________
"The difference between 'involvement' and 'commitment' is
like an eggs-and-ham breakfast:
The chicken was 'involved' - the pig was 'committed'."

http://community.webshots.com/user/godwino

"Dave Bell" wrote in message
...
On Sun, 27 Jul 2003, w_tom wrote:

Let's review where all that energy was applied and how much
- with numbers so that we don't do what junk scientists must
do.

Don Kelly in Newsgroup sci.physics.electromag on 4 Nov 2000
entitled "Oddball question":
over the duration of the storm (and a wide area) ... A typical
stroke will reach its peak in about 1-2 microseconds and die to
about half peak in 50-100 microseconds. Millionths of seconds,
not seconds! There may be several strokes in the same path but
even 3-5 strokes will take less than 1/1000 second. The strokes
just appear to last seconds.
Yes there is a high peak power in a stroke but this does not
translate into appreciable energy (about 55 KWH (200MJ)for an
average stroke). Energy is what we need, not high peak power.

Which, for "Gee Whiz!" value, works out to on the order of 2x10^12 Watts
over 100 uS...

The US Army defines in TM5-690 a wire size sufficient to
discharge lightning without damage. 10 AWG. This makes
complete sense once one learns a direct lightning strike has
so little energy.

Various non commercial websites suggest that a typical lightning
strike releases 250 KWH of energy. A big one may release 10 times
that
much. That is a lot of energy. Admittedly, most of that is
dissipated in the air
above where it strikes, but I think it is disingenuous to
characterize it
as "little".

A lightning rod above the pond and properly earthed by 10
AWG or heavier wire is more than sufficient to intercept and
divert lightning to earth without pond damage.

Most lightning rod manufacturers use 2 or 0 gauge wire as the down
wire.
10 gauge seems to me a little flimsy. Given that a 10 gauge copper
wire has a
resistance of about 1 ohm per 1000 feet, and given a total length
of wire
of about 50 feet, we are dealing with 0.05 ohms of resistance.
Given also
that an average lightning strike can have a current of 10,000 amps
(NASA
has measured at least one strike of 100,000 amps)(and that the
conductor takes
the entire current) we are dealing with a dissipated power of
10000^2*.05
or 5 million watts. Or 100,000 watts per foot of wire. Admittedly
this is
for a very short time. But I submit that 100000 watts applied to a
foot of
this wire over a millisecond will melt or otherwise seriously damage
that
wire.

In addition to the DC resistance, you need to take into account the
inductance of the grounding wire. In the far more limited world of
industrial high energy discharges, an associate observed multiple
instances where a large laser flashlamp power supply was dumped to the
solid copper lab grounding grid. The cable from the crowbar switch to the
grid was about 4 feet long, running perhaps 30 degrees off the vertical.
They would see sparks "shortcut" from 18 inches or more up the cable, to
the floor, rather than continue down the direct path. What's the dry air
breakdown voltage for 18 inches? These *potentials*, with significant
energy behind them, do occur, even with properly grounded equipment!

Dave

Lightning Strike OT? WTH brought this on?
 

Just Me \"Koi\" wrote:
So I read this thread with great anticipation of seeing how it relates to
the subject of this newsgroup! Let's all collectively compliment all these
snooty astro-phycists on their deep knowledge and ask them to go back into
their laboratory so that we can continue to enjoy our hobby!

Just my 2 cents.

actualy it started ontopic as some ones pond got blown out of the ground by lightning



John Rutz
Z5 New Mexico

never miss a good oportunity to shut up

see my pond at:

http://www.fuerjefe.com