lightning grounds
 

You have been reading too many science fiction books. Just a little
common sense will tell you that most of your advice is bogus.

Regards
Gary


On Wed, 28 Jan 2004 00:07:58 GMT, Chuck Bollinger
wrote:

Parallax wrote:

In deep woods during a storm, I sat under a picnic shelter on top of a
dry picnic table on top of dry concrete. It jumped out of a nearby
conduit and to the DRY concrete floor in front of me.

Don't do that again - seriously. Here's the thing: Whether lightning strikes
something isn't related to the item's conductivity but to the amount of charge
it has built up. The arc will go between the highest charge in the cloud/air
and the highest opposite charge on the land. Wet or dry doesn't matter much.
You know this from rubbing a dry glass rod in dry wool or your dry feet across a
dry rug. It's worse the drier things are.

After the strike happens it is no longer a matter of charge, but power. The
amount of damage will depend upon whether there is a good path to earth. That's
where conductivity comes in. If there is no path the amount of 'surface effect'
increases, endangering people and things in the area.

Therefore it would be safer to stand next to a heavy copper flagpole embedded in
the earth than under a tree or in a 'dry' picnic shelter. Me, I'll stay here in
the Pacific NW and take my chances with tsunamis.

method is to try to get it to ground as quickly as possible. I have a
2'X2' copper sheet with a very large tinned copper braid soldered and
crimped to it that I drop overboard. The otehr end of the braid has
two welding clips that I attach to the upper and lower shrouds near
the deck. I turn off and unplug all electronics and stay away from
all metal fittings. I have even considered a retractable Faraday cage
attached to the mast head consisting of small wires to protect the
boat inside it. Am I too paranoid?

No, careful and sensible. The only quarrel I'd have is with braided conductor
to your plate rather than a copper band. Harder to handle, but better capable
of handling the juice. As you live in Florida you might consider having your
plate attached to the hull - tightly with no intervening water - and permanent
connection to your shrouds. The 'air terminal' can be anything - a pointy rod,
those little brush things... etc. I am not familiar with a Faraday cage, but it
sounds knobby. For your purpose you want something sharp, which should have the
effect of allowing static charge to bleed harmlessly off. Then you want a heavy
bonding strap running the length of the boat. Anything important is bonded to
it, at right angles preferably, and the bonding strap is attached to the
underwater ground plate as well.

Essentially with this bypass ground, you are making your boat disappear from the
competition for the lightning.

If lightning does strike then your installation can carry off the charge, but
the whole idea is to avoid static buildup.

However, I am curious about lightning protection for less afflicted
ppl. I have seen these ground plates consisting of sintered bronze
powder that are fairly small but have high surface area due to the
many sintered particles (Dyna-Plate). I can believe these may work
for low E fields and low current but I do not believe they work for
high fields and high currents (like lightning). I think the small
passages act like tiny Faraday cups allowing no field inside and the
effective surface area is not much larger than the external area.
What do others think?

Well, the minimum grounding plate is 1 foot square. Dyna Plates seem to be used
to ground single sideband transmitters. Stick with a copper plate. Two square
feet is overkill but does no harm and perhaps adds a comfort level.

Check into your local Power Squadron. Their educational offerings include
Marine Electronics which covers this subject, including the 'zone of protection'.

http://www.usps.org

lightning grounds
 

In article ,
(Parallax) wrote:

We often see some discussions about lightning protection but here in
FL, it is really a major problem snip
My normal lightning protection
method is to try to get it to ground as quickly as possible. I have a
2'X2' copper sheet with a very large tinned copper braid soldered and
crimped to it that I drop overboard. The otehr end of the braid has
two welding clips that I attach to the upper and lower shrouds near
the deck. I turn off and unplug all electronics and stay away from
all metal fittings. I have even considered a retractable Faraday cage
attached to the mast head consisting of small wires to protect the
boat inside it. Am I too paranoid?

Having lived in Clearwater for 5 years, I'd say "NO!" to being paranoid.
Sometimes they ARE out to get you.

In that area of FL, I'd probably have leads hanging from all 4
"corners", permanently attached with bulldog clamps, not dinky welding
clips ;-) They would be clipped to something while under way. I figure
about 6' of copper strand in the water is sufficient and plates are
bulky, so would use zinc guppies to weigh them down so they could "live"
in the water while we were away from the boat.


However, I am curious about lightning protection for less afflicted
ppl. I have seen these ground plates consisting of sintered bronze
powder that are fairly small but have high surface area due to the
many sintered particles (Dyna-Plate). I can believe these may work
for low E fields and low current but I do not believe they work for
high fields and high currents (like lightning). I think the small
passages act like tiny Faraday cups allowing no field inside and the
effective surface area is not much larger than the external area.
What do others think?

That sounds sorta reasonable to me. Our iron keel is our ground, so I
haven't worried about it much. I believe most people hope that making
the mast "look" like ground with a good Dyna-Plate or similar will
protect them.

Personally, I think that making a Faraday cage out of the shrouds is the
best bet, but there are no guarantees. Friends put one of those bottle
brushes up on the mast -- factory approved tech did it -- and they got
struck a week or so later.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/

lightning grounds
 

In article ,
(Parallax) wrote:

We often see some discussions about lightning protection but here in
FL, it is really a major problem snip
My normal lightning protection
method is to try to get it to ground as quickly as possible. I have a
2'X2' copper sheet with a very large tinned copper braid soldered and
crimped to it that I drop overboard. The otehr end of the braid has
two welding clips that I attach to the upper and lower shrouds near
the deck. I turn off and unplug all electronics and stay away from
all metal fittings. I have even considered a retractable Faraday cage
attached to the mast head consisting of small wires to protect the
boat inside it. Am I too paranoid?

Having lived in Clearwater for 5 years, I'd say "NO!" to being paranoid.
Sometimes they ARE out to get you.

In that area of FL, I'd probably have leads hanging from all 4
"corners", permanently attached with bulldog clamps, not dinky welding
clips ;-) They would be clipped to something while under way. I figure
about 6' of copper strand in the water is sufficient and plates are
bulky, so would use zinc guppies to weigh them down so they could "live"
in the water while we were away from the boat.


However, I am curious about lightning protection for less afflicted
ppl. I have seen these ground plates consisting of sintered bronze
powder that are fairly small but have high surface area due to the
many sintered particles (Dyna-Plate). I can believe these may work
for low E fields and low current but I do not believe they work for
high fields and high currents (like lightning). I think the small
passages act like tiny Faraday cups allowing no field inside and the
effective surface area is not much larger than the external area.
What do others think?

That sounds sorta reasonable to me. Our iron keel is our ground, so I
haven't worried about it much. I believe most people hope that making
the mast "look" like ground with a good Dyna-Plate or similar will
protect them.

Personally, I think that making a Faraday cage out of the shrouds is the
best bet, but there are no guarantees. Friends put one of those bottle
brushes up on the mast -- factory approved tech did it -- and they got
struck a week or so later.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/

lightning grounds
 

Jere Lull wrote in message ...
In article ,
(Parallax) wrote:

We often see some discussions about lightning protection but here in
FL, it is really a major problem snip
My normal lightning protection
method is to try to get it to ground as quickly as possible. I have a
2'X2' copper sheet with a very large tinned copper braid soldered and
crimped to it that I drop overboard. The otehr end of the braid has
two welding clips that I attach to the upper and lower shrouds near
the deck. I turn off and unplug all electronics and stay away from
all metal fittings. I have even considered a retractable Faraday cage
attached to the mast head consisting of small wires to protect the
boat inside it. Am I too paranoid?

Having lived in Clearwater for 5 years, I'd say "NO!" to being paranoid.
Sometimes they ARE out to get you.

My 28' S2 has internal ballast, otherwise I'd use the keel as ground.
Being VERY familiar with high voltage discharges, I use braid because
such discharges have high frequency components so they need a lot of
surface area to carry the current. I considered fastening the copper
directly to the hull with the braid fastened from inside but
considered:

10,000 amps X10,000,000 volts = 10E10 watts dissipatted in about 50
nanoseconds,sorta like hitting your hull with a big sledgehammer.

Thunderstorms in Clearwater may be even worse.

In that area of FL, I'd probably have leads hanging from all 4
"corners", permanently attached with bulldog clamps, not dinky welding
clips ;-) They would be clipped to something while under way. I figure
about 6' of copper strand in the water is sufficient and plates are
bulky, so would use zinc guppies to weigh them down so they could "live"
in the water while we were away from the boat.


However, I am curious about lightning protection for less afflicted
ppl. I have seen these ground plates consisting of sintered bronze
powder that are fairly small but have high surface area due to the
many sintered particles (Dyna-Plate). I can believe these may work
for low E fields and low current but I do not believe they work for
high fields and high currents (like lightning). I think the small
passages act like tiny Faraday cups allowing no field inside and the
effective surface area is not much larger than the external area.
What do others think?

That sounds sorta reasonable to me. Our iron keel is our ground, so I
haven't worried about it much. I believe most people hope that making
the mast "look" like ground with a good Dyna-Plate or similar will
protect them.

Personally, I think that making a Faraday cage out of the shrouds is the
best bet, but there are no guarantees. Friends put one of those bottle
brushes up on the mast -- factory approved tech did it -- and they got
struck a week or so later.

lightning grounds
 

Jere Lull wrote in message ...
In article ,
(Parallax) wrote:

We often see some discussions about lightning protection but here in
FL, it is really a major problem snip
My normal lightning protection
method is to try to get it to ground as quickly as possible. I have a
2'X2' copper sheet with a very large tinned copper braid soldered and
crimped to it that I drop overboard. The otehr end of the braid has
two welding clips that I attach to the upper and lower shrouds near
the deck. I turn off and unplug all electronics and stay away from
all metal fittings. I have even considered a retractable Faraday cage
attached to the mast head consisting of small wires to protect the
boat inside it. Am I too paranoid?

Having lived in Clearwater for 5 years, I'd say "NO!" to being paranoid.
Sometimes they ARE out to get you.

My 28' S2 has internal ballast, otherwise I'd use the keel as ground.
Being VERY familiar with high voltage discharges, I use braid because
such discharges have high frequency components so they need a lot of
surface area to carry the current. I considered fastening the copper
directly to the hull with the braid fastened from inside but
considered:

10,000 amps X10,000,000 volts = 10E10 watts dissipatted in about 50
nanoseconds,sorta like hitting your hull with a big sledgehammer.

Thunderstorms in Clearwater may be even worse.

In that area of FL, I'd probably have leads hanging from all 4
"corners", permanently attached with bulldog clamps, not dinky welding
clips ;-) They would be clipped to something while under way. I figure
about 6' of copper strand in the water is sufficient and plates are
bulky, so would use zinc guppies to weigh them down so they could "live"
in the water while we were away from the boat.


However, I am curious about lightning protection for less afflicted
ppl. I have seen these ground plates consisting of sintered bronze
powder that are fairly small but have high surface area due to the
many sintered particles (Dyna-Plate). I can believe these may work
for low E fields and low current but I do not believe they work for
high fields and high currents (like lightning). I think the small
passages act like tiny Faraday cups allowing no field inside and the
effective surface area is not much larger than the external area.
What do others think?

That sounds sorta reasonable to me. Our iron keel is our ground, so I
haven't worried about it much. I believe most people hope that making
the mast "look" like ground with a good Dyna-Plate or similar will
protect them.

Personally, I think that making a Faraday cage out of the shrouds is the
best bet, but there are no guarantees. Friends put one of those bottle
brushes up on the mast -- factory approved tech did it -- and they got
struck a week or so later.

lightning grounds
 

On Wed, 28 Jan 2004 01:36:19 GMT, Gary Schafer
wrote (with possible editing):

You have been reading too many science fiction books. Just a little
common sense will tell you that most of your advice is bogus.

I'm not trying to start a flame, but as an engineer with many years
involving remote, mountain-top installations, I'd say his advice was
excellent, but I'm always willing to learn: what would you recommend?
--

Larry
Email to rapp at lmr dot com

lightning grounds
 

On Wed, 28 Jan 2004 01:36:19 GMT, Gary Schafer
wrote (with possible editing):

You have been reading too many science fiction books. Just a little
common sense will tell you that most of your advice is bogus.

I'm not trying to start a flame, but as an engineer with many years
involving remote, mountain-top installations, I'd say his advice was
excellent, but I'm always willing to learn: what would you recommend?
--

Larry
Email to rapp at lmr dot com

lightning grounds
 

On Wed, 28 Jan 2004 15:49:38 GMT, L. M. Rappaport
wrote:

On Wed, 28 Jan 2004 01:36:19 GMT, Gary Schafer
wrote (with possible editing):

You have been reading too many science fiction books. Just a little
common sense will tell you that most of your advice is bogus.

I'm not trying to start a flame, but as an engineer with many years
involving remote, mountain-top installations, I'd say his advice was
excellent, but I'm always willing to learn: what would you recommend?


Well for a start, I would not stand next to a copper flag pole or a
tree in a thunder storm. Side arcs can come just as easily from one as
the other.

Standing on the ground near a lightning strike can be deadly. Even if
you are not directly struck. As the strike current travels through the
earth there is a voltage gradient in the earth. In other words in a
distance of a foot or so there can be greatly different voltages on
the surface because of the high current flowing in the earth as the
charge spreads out from the strike point.

Lightning strikes can not be prevented. You can not "make anything
disappear from the competition for lightning".

There is what is called a "cone of protection" under something like a
mast with guys or shrouds. The lightning will hit those first before
what is underneath.

There is no such thing as bleeding of the charge. The earth can supply
charge much faster than it is possible to bleed it off.

A blunt air terminal is preferred over a sharp pointed one. A sharp
point will encourage streamers to form sooner. They can actually
attract a strike. This includes the toilet brushes mounted on the
mast.

The amount of voltage across an object associated with a lightning
strike is dependent on the amount of the current contained in the
strike.

Lightning is a constant current source.
A strike contains a given amount of current. Depending on how good the
conductor is that it strikes determines the amount of voltage
developed across it. The better the conductor the less voltage seen
across it. But the amount of current will be approximately the same.
In other words the voltage will rise high enough in order to produce
the strike current through the conductor. The higher resistance the
conductor the higher the voltage seen.

The reason for a low impedance ground conductor / system is to keep
the voltage rise to a minimum to prevent side flashes to other things.

The mast and all shrouds on a boat should be grounded. Each should
have their own run, as straight as possible, to the ground.
A common "ground buss" is not desirable as a considerable voltage rise
can also occur on the ground buss. It is better to have separate runs
to the ground for whatever you are grounding. And no 90 degree turns.

The mast and each shroud will share the current in a strike. Just
grounding the shrouds will not provide a sufficient path to ground.
Each has resistance, and worse, high inductance. This provides a high
impedance path for the sharp rise time lightning.

The high impedance path allows the voltage to rise very high at the
top of the mast. If the mast is not grounded at the bottom that will
allow the bottom of the mast to also rise high with voltage. It will
arc over to whatever is closer to ground in the boat.
Just grounding the mast provides the same problem with the shrouds if
they are not grounded. The mast also presents a high impedance to the
lightning even though it is quite large in surface area.

Large surface area conductors are desired for lightning current
carriers because of their lower inductance. It does not matter if they
are solid wire, stranded wire, braided strap or solid strap. The
amount of surface area is what is important to reduce inductance. The
only problem with braided strap is that it corrodes much faster than
solid strap.

Several wires or strap can be put in parallel for additional
inductance reduction


That should do for a start. :)

Regards
Gary

lightning grounds
 

On Wed, 28 Jan 2004 15:49:38 GMT, L. M. Rappaport
wrote:

On Wed, 28 Jan 2004 01:36:19 GMT, Gary Schafer
wrote (with possible editing):

You have been reading too many science fiction books. Just a little
common sense will tell you that most of your advice is bogus.

I'm not trying to start a flame, but as an engineer with many years
involving remote, mountain-top installations, I'd say his advice was
excellent, but I'm always willing to learn: what would you recommend?


Well for a start, I would not stand next to a copper flag pole or a
tree in a thunder storm. Side arcs can come just as easily from one as
the other.

Standing on the ground near a lightning strike can be deadly. Even if
you are not directly struck. As the strike current travels through the
earth there is a voltage gradient in the earth. In other words in a
distance of a foot or so there can be greatly different voltages on
the surface because of the high current flowing in the earth as the
charge spreads out from the strike point.

Lightning strikes can not be prevented. You can not "make anything
disappear from the competition for lightning".

There is what is called a "cone of protection" under something like a
mast with guys or shrouds. The lightning will hit those first before
what is underneath.

There is no such thing as bleeding of the charge. The earth can supply
charge much faster than it is possible to bleed it off.

A blunt air terminal is preferred over a sharp pointed one. A sharp
point will encourage streamers to form sooner. They can actually
attract a strike. This includes the toilet brushes mounted on the
mast.

The amount of voltage across an object associated with a lightning
strike is dependent on the amount of the current contained in the
strike.

Lightning is a constant current source.
A strike contains a given amount of current. Depending on how good the
conductor is that it strikes determines the amount of voltage
developed across it. The better the conductor the less voltage seen
across it. But the amount of current will be approximately the same.
In other words the voltage will rise high enough in order to produce
the strike current through the conductor. The higher resistance the
conductor the higher the voltage seen.

The reason for a low impedance ground conductor / system is to keep
the voltage rise to a minimum to prevent side flashes to other things.

The mast and all shrouds on a boat should be grounded. Each should
have their own run, as straight as possible, to the ground.
A common "ground buss" is not desirable as a considerable voltage rise
can also occur on the ground buss. It is better to have separate runs
to the ground for whatever you are grounding. And no 90 degree turns.

The mast and each shroud will share the current in a strike. Just
grounding the shrouds will not provide a sufficient path to ground.
Each has resistance, and worse, high inductance. This provides a high
impedance path for the sharp rise time lightning.

The high impedance path allows the voltage to rise very high at the
top of the mast. If the mast is not grounded at the bottom that will
allow the bottom of the mast to also rise high with voltage. It will
arc over to whatever is closer to ground in the boat.
Just grounding the mast provides the same problem with the shrouds if
they are not grounded. The mast also presents a high impedance to the
lightning even though it is quite large in surface area.

Large surface area conductors are desired for lightning current
carriers because of their lower inductance. It does not matter if they
are solid wire, stranded wire, braided strap or solid strap. The
amount of surface area is what is important to reduce inductance. The
only problem with braided strap is that it corrodes much faster than
solid strap.

Several wires or strap can be put in parallel for additional
inductance reduction


That should do for a start. :)

Regards
Gary

lightning grounds
 

Gary Schafer wrote:

Well for a start, I would not stand next to a copper flag pole or a
tree in a thunder storm. Side arcs can come just as easily from one as
the other.

Nor would I. My fault for not putting in a smiley face. But it is true that it
would be safer to be nearer a grounded pole than a tree, owing to the reduced
"surface effect" of the better conductor. That is to say: If one were somehow
standing half way between a copper flagpole and a tree, it would be advisable to
edge nearer the flag pole. That does not mean one should lean on it, though.
There will be surface effect around even the best conductor.

Lightning strikes can not be prevented. You can not "make anything
disappear from the competition for lightning".

Agree - not 'disappear', but unquestionably a proper air terminal and its corona
discharge will reduce build-up of positive charge. If there is something in the
area which is not so good at getting rid of charge, it will more likely be hit.
See below:

There is no such thing as bleeding of the charge. The earth can supply
charge much faster than it is possible to bleed it off.

"SUBSTANTIATION: In the years since Franklin Invented the sharp lightning rod,
many physicists have shown that, under strong electric fields, the air around
sharp rods becomes Ionized, creating space charges that act to weaken the
fields. It has also been discovered that the strengths of the strong fields
around the tips or sharp rods decrease so rapidly with distance that they become
weaker than the fields over blunter rods at distances greater than about 1/4 in.
.... From laboratory and field experiments, we have established that the critical
field strengths for lightning Interception develop sooner around blunt lightning
rods than around sharp ones around which the field strengths are limited by
their charge emissions. In effect. sharp rods tend to protect themselves, by
their charge emissions, against participating in lightning strikes."
Charles B. Moore, Langmuir Laboratory, New Mexico Tech
------------------

A blunt air terminal is preferred over a sharp pointed one. A sharp
point will encourage streamers to form sooner. They can actually
attract a strike. This includes the toilet brushes mounted on the
mast.

Here is a quote from a study by scientists who were *trying* to attract
lightning strikes:
------------
In strike-reception competitions over the past six years between sharp
Franklin rods, sharp-tipped "ESE" air terminals, and blunt rods with
hemispherical tips, all mounted on 6-mater high masts and separated
horizontally by about 6 meters, none of the sharp-tipped air terminals has
been "struck" by lightning but 12 of the blunt rods have taken strikes.
-------------------------
SUMMARY (Dinner is on the table):

You seem to have quite a bit of insight into lightning, but your message jumps
around a bit, and this is all I have time for. My purpose was not a detailed
rebuttal but to demonstrate that your original cryptic remark "...advice is
bogus" was not in the best spirit or interst of reasoned dialog, nor was it
true. From your follow-up message it appears you are more ready to bring more
light than heat. Good. Grownups can disagree and discuss those points of
contention without resorting to name-calling and invective.