I am trying to gain a better understanding of the issues associated
with lightning and grounding, particularly for an amateur radio
station. I would greatly appreciate any answers to my questions, given
below.

1.) It seems like lightning "finds" a path before actually discharging
through it. Is this correct? How fast is the process of finding the
path?

2.) Does lightning discharge over one path or many paths? In other
words, if lightning strikes a point, and there are two paths from that
point to ground, is the energy shared - like a current divider? One
would think that this is what happens, with the sharing based upon
relative impedances to ground.

3.) This talk about "single point ground" can be confusing, especially
when the solution involves multiple ground rods. I believe we are
really saying that the station (equipment) should be connected to
ground at only one point - but you can have any number of ground
connections (i.e., like ground rods) otherwise.

4.) Does the size of an antenna affect the probability of its being
struck by lightning, all else being equal? What is the governing
relationship?

5.) Finally, consider an amateur antenna on a pole, located some
distance from the service entrance of the house. Let's say there is a
copper cold water pipe right at the service entrance. Is it wise to
place a lightning rod (or rods) right under the antenna, place an
arrestor on the coax there and then another arrestor where the coax
enters at the service entrance? Is a ground wire needed between the
remote ground rod and the cold water pipe?

Thanks in advance,

-JJ

wrote
I am trying to gain a better understanding of the issues associated
with lightning and grounding, particularly for an amateur radio
station. I would greatly appreciate any answers to my questions, given
below.

1.) It seems like lightning "finds" a path before actually discharging
through it. Is this correct? How fast is the process of finding the
path?

I have 5 minutes before supper to answer this, so it is an off-the-cuff
answer which you can look up in greater and possibly more accurate detail
later:

For several minutes before a thunderstorm arrives, it pushes a massive
wavefront of positive ions over the surface of the earth. This ion "wave"
saturates all objects and they begin to emit positive-charged "streamers"
skyward toward the thunderstorm cloud. Every object with these positive ions
(rocks, buildings, trees, human heads, etc) allows these streamers. Minutes
(or seconds) later, a stepped-leader from a cloud will start earthward and
the attraction to several of those streamers will grow. Hair could stand up
on your neck when this happens. Seconds or parts of a second later, a
step-leader will launch from the most favorable of those upward-flowing
positive-ion streamers, and the stepped leader will connect to it. A small
visible explosion is seen and heard about 150' above ground as this happens
(film shows this) and the cloud opens a channel of current to that stepped
leader. Milliseconds later a RETURN SROKE from the ground to the cloud opens
that stepped leader path wide open, and another pusle or two or three may
occur from cloud to ground following that. Lightning has "struck".


2.) Does lightning discharge over one path or many paths? In other
words, if lightning strikes a point, and there are two paths from that
point to ground, is the energy shared - like a current divider? One
would think that this is what happens, with the sharing based upon
relative impedances to ground.

Yes multiple paths are likely in most strikes. Current division occurs even
through air, we call it voltage division when more than one branch connects
with earth, as the current flowing (10-50ka) will be divided according to
the varying voltage potentials felt at various points. Voltage division is a
good thing when it is where we want it to be. Current then flows on
conductors of our choosing!


3.) This talk about "single point ground" can be confusing, especially
when the solution involves multiple ground rods. I believe we are
really saying that the station (equipment) should be connected to
ground at only one point - but you can have any number of ground
connections (i.e., like ground rods) otherwise.

That's correct. Ideally there would only be one single point ground for an
entire structure. But when radio room and AC service entrance grounds are
far apart, we bnd them and connect all forms of grounding systems along the
way.


4.) Does the size of an antenna affect the probability of its being
struck by lightning, all else being equal? What is the governing
relationship?

No, but the HEIGHT above ground does. Any object that a rolling ball 300' in
diameter would touch as it was "rolled" over your property, is an object
that is most likely to be struck if lightning occurs in that general area.
Lightning can sideflash horizontally for hundreds of feet, and even change
direction more drastically, but the rolling ball defines most likely
attachment points for a strike.


5.) Finally, consider an amateur antenna on a pole, located some
distance from the service entrance of the house. Let's say there is a
copper cold water pipe right at the service entrance. Is it wise to
place a lightning rod (or rods) right under the antenna, place an
arrestor on the coax there and then another arrestor where the coax
enters at the service entrance? Is a ground wire needed between the
remote ground rod and the cold water pipe?

A "Lighttning Rod" is a roof top or other high fastened "collector" of
lightning. The modern name for this is an "Air Terminal". From a lightning
rod, bonded "Down Conductors" carry the lightning energy to a "Grounding
Electrode" (Ground Rod).

A tower is already a lightning "air terminal" and all it needs is a good
ground system to divide the vltage and curent in as wide an area as
possible. Even the coax shield must be grounded many times along the height
of the tower, and an arrestor (or surge protection device) could be attached
at the base of the tower also. Yes it would also be used (as is shield
grounding) at the entrance to the structure.

Cold water pipes may be bonded as additional voltage division in a lightning
protection ground system, but they are only the source of primary single
point ground IF the structure's AC service entrance uses them as such.


Thanks in advance,

-JJ


More details are explained at:

http://members.cox.net/pc-usa/station/ground0.htm

Cheers,

Jack Painter
Virginia Beach, Virginia

Lets start by first adjusting the perspective. CG lightning
seeks charges located 5 kilometers over there. Therefore the
shortest electrical path is 3 kilometers directly down to
tree, antenna, or utility wire. Then 4 kilometers through
earth to those charges. Where will lightning strike earth?
Answer is better found in geology. What is the more
conductive earth? Has a transcontinental pipeline changed the
electrical nature of that region? Obviously the answer is not
always obvious. Then many assume lightning is capricious.

Some campers slept near a tree when that tree was struck.
Those sleeping tangential to the tree were not affected.
Those sleeping pointed at the tree required medical
treatment. An electrical path was down tree, through earth,
up into human body at the feet, out of human body at the head,
then onwards to earth borne charges located elsewhere.

IOW, the camper who required medical treatment were, in
essence, earthed at two separate points (at foot and head).

Suppose we had surrounded the camper with a buried electric
wire loop. IOW the conductive path was around the sleeping
camper. A single point ground (equipotential) was created
beneath the camper.

Single point ground can be a single earth ground rod at one
of the building, or it can be accomplished by making earth
beneath equipotential. But it comes back to a basic concept.
No current flows if an incoming and outgoing path does not
exist. Goes right back to elementary school science that
defined electricity. First a complete circuit must exist
meaning that each component must have both an incoming and
outgoing path.

The concept of single point ground is make only one
connection so that both incoming and outgoing paths do not
exist. Some examples of how this is accomplished:
http://www.erico.com/public/library/...es/tncr002.pdf
http://www.cinergy.com/surge/ttip08.htm

http://lists.contesting.com/archives.../msg00644.html
http://lists.contesting.com/_towerta...il/004413.html
http://www.leminstruments.com/pdf/LEGP.pdf (see page 14)

How multiple earth grounds can cause damage to a fax:
http://www.epri-peac.com/tutorials/sol01tut.html

Notice even a buried wire can carry destructive transients
as demonstrated by the phone wire in that erico.com figure.
Even a buried wire must connect to the single point earth
before entering a building so that all wires enter at the
single point:
http://www.polyphaser.com/ppc_TD1023.aspx

wrote:
I am trying to gain a better understanding of the issues associated
with lightning and grounding, particularly for an amateur radio
station. I would greatly appreciate any answers to my questions, given
below.

1.) It seems like lightning "finds" a path before actually discharging
through it. Is this correct? How fast is the process of finding the
path?

2.) Does lightning discharge over one path or many paths? In other
words, if lightning strikes a point, and there are two paths from that
point to ground, is the energy shared - like a current divider? One
would think that this is what happens, with the sharing based upon
relative impedances to ground.

3.) This talk about "single point ground" can be confusing, especially
when the solution involves multiple ground rods. I believe we are
really saying that the station (equipment) should be connected to
ground at only one point - but you can have any number of ground
connections (i.e., like ground rods) otherwise.

4.) Does the size of an antenna affect the probability of its being
struck by lightning, all else being equal? What is the governing
relationship?

5.) Finally, consider an amateur antenna on a pole, located some
distance from the service entrance of the house. Let's say there is a
copper cold water pipe right at the service entrance. Is it wise to
place a lightning rod (or rods) right under the antenna, place an
arrestor on the coax there and then another arrestor where the coax
enters at the service entrance? Is a ground wire needed between the
remote ground rod and the cold water pipe?

Thanks in advance,

-JJ

wrote in message
oups.com...
I am trying to gain a better understanding of the issues associated
with lightning and grounding, particularly for an amateur radio
station. I would greatly appreciate any answers to my questions, given
below.

1.) It seems like lightning "finds" a path before actually discharging
through it. Is this correct? How fast is the process of finding the
path?

no, it takes all the possible 'paths' at once. ones that end in high
impedances reflect most of the current back and then it goes down some other
path... ones that end in low impedances suck more current out of the system.


2.) Does lightning discharge over one path or many paths? In other
words, if lightning strikes a point, and there are two paths from that
point to ground, is the energy shared - like a current divider? One
would think that this is what happens, with the sharing based upon
relative impedances to ground.

yes, as above... it goes down all paths and ends up sharing them based on
relative impedance exactly like a current divider but with time delays based
on the lengths of the paths and terminating impedance.


3.) This talk about "single point ground" can be confusing, especially
when the solution involves multiple ground rods. I believe we are
really saying that the station (equipment) should be connected to
ground at only one point - but you can have any number of ground
connections (i.e., like ground rods) otherwise.

yeah, thats a reasonable way to look at it. it kind of looks like an
hourglass with everything being connected at one common point and spreading
out in the shack on one side and into the ground on the other side but
possibly with multiple connections on both sides.


4.) Does the size of an antenna affect the probability of its being
struck by lightning, all else being equal? What is the governing
relationship?

the bigger it is the more likely it is to get hit.


5.) Finally, consider an amateur antenna on a pole, located some
distance from the service entrance of the house. Let's say there is a
copper cold water pipe right at the service entrance. Is it wise to
place a lightning rod (or rods) right under the antenna, place an
arrestor on the coax there and then another arrestor where the coax
enters at the service entrance? Is a ground wire needed between the
remote ground rod and the cold water pipe?

this is actually a couple (relatively) unrelated questions.

the more rods the merrier. the more paths you can give lightning the less
of it will get into your shack. just don't put the rods too close together
or you are wasting money, put them at least their own length apart from each
other and connect by heavy wire, cadwelded, etc, etc.

yes, you can put arresters at each end of a cable, but its probably only
worth it if the cable is relatively long... on a swag i would say if its
shorter than 100' its probably not worth two arresters, just put one at the
service entrance. the function of an 'arrester' is to just equalize the
voltage between the shield and center conductor and since the critical point
for that difference is at the radio end that one is more important.

i believe code requires water pipes to be connected to the service entrance
ground. the service entrance ground should also be connected to the ground
at the antenna, so indirectly the water pipe and remote rod would be
connected.


Thanks in advance,

-JJ

wrote in message
oups.com...
I am trying to gain a better understanding of the issues associated
with lightning and grounding, particularly for an amateur radio
station. I would greatly appreciate any answers to my questions, given
below.

1.) It seems like lightning "finds" a path before actually discharging
through it. Is this correct? How fast is the process of finding the
path?

Logic says no. As a charge starts to build, it also starts to flow. If the
discharge path has high enough resistance, it wont flow until the charge
reaches a certain potential. That may be what you were trying to ask. Then
we are speaking of a dielectric. When the potential becomes large enough to
punch through the dielectric, then the discharge occurs.

2.) Does lightning discharge over one path or many paths? In other
words, if lightning strikes a point, and there are two paths from that
point to ground, is the energy shared - like a current divider? One
would think that this is what happens, with the sharing based upon
relative impedances to ground.

No need to make lightening too mysterious. It is electricity, and if there
are two solid paths of basically equal resistant, it will flow in both. It
is important to note that I did say basically EQUAL. Two paths may be equal
at low voltages, but at high voltages, in bends of wire, the lightening has
been known to burn off one path.

3.) This talk about "single point ground" can be confusing, especially
when the solution involves multiple ground rods. I believe we are
really saying that the station (equipment) should be connected to
ground at only one point - but you can have any number of ground
connections (i.e., like ground rods) otherwise.

I cant tell you much about this. Its safer for the equipment to have only
one ground connection as the surge caused by lightening can enter from any
of the grounds if its not a direct hit to the antenna itself.

4.) Does the size of an antenna affect the probability of its being
struck by lightning, all else being equal? What is the governing
relationship?

Again, logic dictates that a bigger antenna can be closer to a charged area
than a small one. That being said, it probably doesnt make much difference
unless youre running some very longwire type of antennas. A yagi or a quad
will probably not change the chance of getting a hit very much.

5.) Finally, consider an amateur antenna on a pole, located some
distance from the service entrance of the house. Let's say there is a
copper cold water pipe right at the service entrance. Is it wise to
place a lightning rod (or rods) right under the antenna, place an
arrestor on the coax there and then another arrestor where the coax
enters at the service entrance? Is a ground wire needed between the
remote ground rod and the cold water pipe?

Thanks in advance,

-JJ

Don't connect it to your water pipe. That's a good way to get a damaged
water pipe if you take a hit. Use grounding at the antenna support. You CAN
use arrestors, but the way our hardline at work is grounded, they just trim
off the outer jacket and connect a clamp for grounding, then cover it with
weatherproof putty. They are grounded at the base of the antenna tower, then
at the point of entry to the cellsite. Then there is a ring ground inside
the cellsite, and that ring ground is connected to a groundrod outside the
site at the opposite corner from where the antenna feedlines enter. Cant
explain how it works all that well, but we seldom have much lightening
damage to our equipment, and its directly connected all the time. We do use
surge protection to protect the power wiring to the equipment as well. There
are probably others on here that can give you more info than I can. There
are also standards that are set up by NEC that need to be followed as well,
if I'm not mistaken.
B

wrote in message
oups.com...
I am trying to gain a better understanding of the issues associated
with lightning and grounding, particularly for an amateur radio
station. I would greatly appreciate any answers to my questions, given
below.

1.) It seems like lightning "finds" a path before actually discharging
through it. Is this correct? How fast is the process of finding the
path?

2.) Does lightning discharge over one path or many paths? In other
words, if lightning strikes a point, and there are two paths from that
point to ground, is the energy shared - like a current divider? One
would think that this is what happens, with the sharing based upon
relative impedances to ground.

3.) This talk about "single point ground" can be confusing, especially
when the solution involves multiple ground rods. I believe we are
really saying that the station (equipment) should be connected to
ground at only one point - but you can have any number of ground
connections (i.e., like ground rods) otherwise.

4.) Does the size of an antenna affect the probability of its being
struck by lightning, all else being equal? What is the governing
relationship?

5.) Finally, consider an amateur antenna on a pole, located some
distance from the service entrance of the house. Let's say there is a
copper cold water pipe right at the service entrance. Is it wise to
place a lightning rod (or rods) right under the antenna, place an
arrestor on the coax there and then another arrestor where the coax
enters at the service entrance? Is a ground wire needed between the
remote ground rod and the cold water pipe?

Thanks in advance,

-JJ

Oh and as a caveat, this is only my opinion from what I have studied and
seen. It is by no means advice as to what you should do in your case. NEC
are the ones that set the standards and inspectors are probably the best
ones to tell you what has to be done.
B

"w_tom" wrote

Lets start by first adjusting the perspective.

You were going strong until you drove off the road and into the ditch right
he

Single point ground can be a single earth ground rod at one
of the building, or it can be accomplished by making earth
beneath equipotential. But it comes back to a basic concept.
No current flows if an incoming and outgoing path does not
exist. Goes right back to elementary school science that
defined electricity. First a complete circuit must exist
meaning that each component must have both an incoming and
outgoing path.

The concept of single point ground is make only one
connection so that both incoming and outgoing paths do not
exist. Some examples of how this is accomplished:

Best remove that whole paragraph from your lightning vocabulary and pretend
you never saw it before. It is completely incorrect and misleading to allude
that lack of a path or circuit will protect anything from lightning. The
opposite is true.

The bonding of all nearby electrically conductive objects is what makes them
equipotential, because current does not flow when there is no potential
between bonded equipments. Interrupting the "circuit" by failing to properly
bond will allow massive potentials and lightning will find several paths you
should have known about and others you never knew possible.

Creating "Equipotential" (bonding) and "Grounding" are two distinctly
seperate principles. Both are required in a system of lightning protection.
If there was one that was immensely more important than the other, it would
be the bonding. A well bonded system "could" survive direct lightning
strikes to the structure with no damage to the equipment even if there was
never a ground connection made (happens to airplannes frequenty). But no
ground system conceivable can allow an equipment room that is not properly
bonded to survive a strike. Applying the two principles of bonding and
grounding together (and surge protection), is what helps control all the
entrance and exit paths for lightning, and makes a lightning protection
"system".

Jack

A well bonded system means all those other potential
'outgoing' paths are connected to the same 'incoming' path.
IOW bonding converts all other possible electrical paths into
the same, common incoming path. If all circuit paths only
connect to the same 'incoming' path, then there is no outgoing
path necessary to conduct electricity.

This is also why equipotential grounding works. But this is
arguing semantics. Bottom line is the perspective of a
protected circuit. If all incoming paths are properly bonded
to a same point, then no outgoing path exists. No outgoing
path means no destructive electricity flow through that
circuit. Therefore no damage.

Jack Painter wrote:
You were going strong until you drove off the road and into the
ditch right he

Single point ground can be a single earth ground rod at one
of the building, or it can be accomplished by making earth
beneath equipotential. But it comes back to a basic concept.
No current flows if an incoming and outgoing path does not
exist. Goes right back to elementary school science that
defined electricity. First a complete circuit must exist
meaning that each component must have both an incoming and
outgoing path.

The concept of single point ground is make only one
connection so that both incoming and outgoing paths do not
exist. Some examples of how this is accomplished:

Best remove that whole paragraph from your lightning vocabulary and
pretend you never saw it before. It is completely incorrect and
misleading to allude that lack of a path or circuit will protect
anything from lightning. The opposite is true.

The bonding of all nearby electrically conductive objects is wha
makes them equipotential, because current does not flow when there
is no potential between bonded equipments. Interrupting the
"circuit" by failing to properly bond will allow massive potentials
and lightning will find several paths you should have known about
and others you never knew possible.

Creating "Equipotential" (bonding) and "Grounding" are two
distinctly seperate principles. Both are required in a system of
lightning protection. If there was one that was immensely more
important than the other, it would be the bonding. A well bonded
system "could" survive direct lightning strikes to the structure
with no damage to the equipment even if there was never a ground
connection made (happens to airplannes frequenty). But no ground
system conceivable can allow an equipment room that is not properly
bonded to survive a strike. Applying the two principles of bonding
and grounding together (and surge protection), is what helps
control all the entrance and exit paths for lightning, and makes a
lightning protection "system".

Jack

All about lightning and grounding at Polyphaser URL:
http://www.polyphaser.com/ppc_ptd_home.aspx


--
Lamont Cranston

J.J. wrote:
"1.) It seems like lightning "finds" a parh before discharging through
it."

Speculation is tempting. I would not swear to a sequence of events but
J.J.`s scenario seems plausible.

Lightning breaks down the dielectric of the atmosphere at some point
where the potentiaal gradient initiates a huge arc. Charges are
accumulating and moving about until an ignition potential is reached at
some point.

Influence of accumulations of charges and their movements must be
propagated at the speed of light, thought by many to be the final speed
limit. Communication of electromagnetic forces among the atmospheric
charges may be considered "finding a path" for the lightning bolt.

Best regards, Richard Harrison, KB5WZI