"Gary Schafer" wrote
What isolates the shield of the coax from carrying current?
As long as it is connected to the tower at one end it is going to have
strike current on it whether you want it there or not. Nothing you can
do about it. Paralleling other conductors will reduce it's total
current but you still have to deal with it on the coax line.

Incorrect. First, a strike termination device is placed higher than other
equipment with its own down conductor. Then a lightning arrestor and shield
bonding are specified at the top of the tower, shield bonding along the path
(up to three times) and at the bottom, then more shield grounding and
another lightning arrestor at the facility entrance.

If you don't want to call the coax shield a grounding conductor that's
ok but that won't stop the current on it.

Current is maintained at a safe level on the coax center conductor and
shielding by the above.

Who told you that you should put lightning protectors at the tower as
well as at the building entrance? What good do you think they do at
the tower other than cost more money?

National telecommunication companies who specify them in white papers and
engineering plans for lightning protection. I have been studying these
systems for 18 months now and find this procedure consistently applied. The
specific information is proprietary but all I had to do was ask for it. I
found the information available via the USAF and other agencies I normally
deal with was somewhat old, so I started asking commercial companies what
they currently use, and could I have copies of their plans. That's where
this information comes from. That and the National Electrical Code and
National Fire Protection Association, October 2004 editions. Studying the
NEC 250 grounding and bonding and the NFPA-780 offers more information to
safely operate communication sequipment, especially during thunderstorms,
than all the amatuer radio operators advice put together. Most of the
amatuers giving this advice have no personal understanding of why or how
this works, they just repeat stories or instructions they heard from someone
else. Probably the biggest collection of dangerous information ever shared
is what hams offer about lightning protection. Even the ARRL which makes an
incredible effort to educate at the issue, has information so old in many
cases it has not been used in best available practice for over ten years.

With buried coax the ground acts like a large choke on the cable also.
Exactly what you want. The ground increases the cables natural
inductance.
/clipped

Your mistaken on this stuff Gary, we either shed or prevent lightning energy
from coax by shield grounding, surge protection devices and sometimes
encasement in grounded conduit. No plan or specification calls for
earth-burying coax to deliver what you promise, and I believe your theory is
electrically impossible, unless as I said over and over, the dialectric
breakdown occurs, which means the installation was improper in the first
place, or overcome by statistically rare events.

73,
Jack Painter
Virginia Beach VA

On Mon, 22 Nov 2004 22:42:20 -0500, "Jack Painter"
wrote:

"Gary Schafer" wrote
What isolates the shield of the coax from carrying current?
As long as it is connected to the tower at one end it is going to have
strike current on it whether you want it there or not. Nothing you can
do about it. Paralleling other conductors will reduce it's total
current but you still have to deal with it on the coax line.

Incorrect. First, a strike termination device is placed higher than other
equipment with its own down conductor. Then a lightning arrestor and shield
bonding are specified at the top of the tower, shield bonding along the path
(up to three times) and at the bottom, then more shield grounding and
another lightning arrestor at the facility entrance.

If you don't want to call the coax shield a grounding conductor that's
ok but that won't stop the current on it.

Current is maintained at a safe level on the coax center conductor and
shielding by the above.

Who told you that you should put lightning protectors at the tower as
well as at the building entrance? What good do you think they do at
the tower other than cost more money?

National telecommunication companies who specify them in white papers and
engineering plans for lightning protection. I have been studying these
systems for 18 months now and find this procedure consistently applied. The
specific information is proprietary but all I had to do was ask for it. I
found the information available via the USAF and other agencies I normally
deal with was somewhat old, so I started asking commercial companies what
they currently use, and could I have copies of their plans. That's where
this information comes from. That and the National Electrical Code and
National Fire Protection Association, October 2004 editions. Studying the
NEC 250 grounding and bonding and the NFPA-780 offers more information to
safely operate communication sequipment, especially during thunderstorms,
than all the amatuer radio operators advice put together. Most of the
amatuers giving this advice have no personal understanding of why or how
this works, they just repeat stories or instructions they heard from someone
else. Probably the biggest collection of dangerous information ever shared
is what hams offer about lightning protection. Even the ARRL which makes an
incredible effort to educate at the issue, has information so old in many
cases it has not been used in best available practice for over ten years.

With buried coax the ground acts like a large choke on the cable also.
Exactly what you want. The ground increases the cables natural
inductance.
/clipped

Your mistaken on this stuff Gary, we either shed or prevent lightning energy
from coax by shield grounding, surge protection devices and sometimes
encasement in grounded conduit. No plan or specification calls for
earth-burying coax to deliver what you promise, and I believe your theory is
electrically impossible, unless as I said over and over, the dialectric
breakdown occurs, which means the installation was improper in the first
place, or overcome by statistically rare events.

73,
Jack Painter
Virginia Beach VA


Jack,

I don't think you really understand all you are reading. It sounds
like you are digging up stuff designed to sell a lot of protection
devices.

As far as the NEC requiring grounding and bonding of structures, They
want to be sure that there is a continuous bond on things they are
concerned with. They don't always consider what they are grounding.

Do you really think that placing a down conductor of #6 wire on a
tower with a 6 or 8 foot face (big tower) is going to make any
difference in the impedance path that the lightning is going to see.
Each leg may be 2 or 3" in diameter itself. The impedance of the tower
will be so much lower than that wire. The lightning won't know the
difference whether that wire is there or not.

Even if the added down conductor did carry a large part of the current
it would get coupled to the tower anyway before it reached the bottom.
That is what happens to the coax lines in reverse. Any energy that the
tower is carrying is coupled to the coax lines whether they are
grounded to the tower or not. You ground them at multiple points to
prevent flashovers between the lines and the tower.

You can not keep the lightning energy off the coax lines or any other
lines coming down the tower. They are all mutual. When those lines
leave the tower at the bottom they are going to have some energy on
them unless you have a perfect ground at the bottom of the tower.

A grounded antenna will keep voltage levels on the center conductor at
a safe level. No need for a protection device at the top.

I agree that there is a lot of mis-information on lightning floating
around. But don't cut all the hams short either. Some of them have
lots of experience in this area.
Think about what you read rather than taking in mounds of propaganda
and repeating it.

Do you think that you can bury the feed wire for your long wire
antenna and have it work very well? What do you think will happen to
the RF on it? Will it make it all the way back to your receiver the
same as it would if it were above ground?

73
Gary K4FMX

Gary,

As far as the NEC requiring grounding and bonding of structures, They
want to be sure that there is a continuous bond on things they are
concerned with. They don't always consider what they are grounding.

Do you really think that placing a down conductor of #6 wire on a
tower with a 6 or 8 foot face (big tower) is going to make any
difference in the impedance path that the lightning is going to see.

I never suggested such a silly thing! You mistake an earlier reference I
made to a bonding conductor. Down conductors are sized according to code
standards which provides a minimum for given elevation categories. 3/0 wire
which is close to 1/2" in dia is the largest reqirement in NEC sizing table
250.66. In telecommunication applications, down conductors are normally
sized to equal or exceed the size of the feed lines, and this means larger
sizing yet. It's bonding conductors that burying usually serves no purpose
except protection. One bond that is an exception is the station ground to
utility entrance ground - that bond will carry ground potential rise current
that hopefully bypasses the power connection at the back of station
equipment. It must remain low impedance and high current capability, so
additional ground rods are required along that bond if farther than 20'.
Don't sell the NEC short. NFPA, which oversees the National Electrical Code,
doesn't specify maximum protection, it specifies minimum protection
standards. Industry does better where it sees cost benefit from doing so.

Even if the added down conductor did carry a large part of the current
it would get coupled to the tower anyway before it reached the bottom.
That is what happens to the coax lines in reverse. Any energy that the
tower is carrying is coupled to the coax lines whether they are
grounded to the tower or not. You ground them at multiple points to
prevent flashovers between the lines and the tower.

Actually this is bonding Gary, an important distinction to understand. A
device is only grounded at a grounding electrode. All other connections are
bonding for equipotential, to minimize voltage differences. The principles
of bonding are not taught in the amateur radio or any other communications
hobby. Only electrical enginners, electricians, and anyone who studies the
electrical code and reference materials on bonding and grounding will
understand this. It's hard to even communicate about lightning protection
until the basics of protection by equipotential are understood, and this
doesn't come from a casual read or anything learned in ham-world postings.
At least not from what I've seen, which is about everything a search engine
can find.


You can not keep the lightning energy off the coax lines or any other
lines coming down the tower. They are all mutual. When those lines
leave the tower at the bottom they are going to have some energy on
them unless you have a perfect ground at the bottom of the tower.

A grounded antenna will keep voltage levels on the center conductor at
a safe level. No need for a protection device at the top.

I didn't write the specifications that major companies are using, and
neither did the companies selling lightning protection, although I agree
there is influence there. Professional Engineers write these to protect
equipment, personnel, and maintain operations, maybe not in that order. If
they specify arrestors at tower tops, they must be trying to avoid damage
that was not protected without them. It is no guarantee that damage is
eliminated by their presence, I'm just relaying their usage - now.


I agree that there is a lot of mis-information on lightning floating
around. But don't cut all the hams short either. Some of them have
lots of experience in this area.

I don't cut all hams short. Richard Harrison (resident guru here on RRA) and
others are thanked on my website for great information, their experiences,
and helpful answers to questions. Many hams provided me with details about
damage to equipment, and their humble honesty cannot be thanked enough. I
have written many the best of the amateur websites discussing grounding and
offered suggestions and references to improve their quality .

Here are a few excerpts you or others may have missed from the NEC:

Article 810.51 of the current NFPA 70, which states in part...

"810.58 Grounding Conductors - Amateur Transmitting and Receiving Stations.

Grounding conductors shall comply with 810.58(A) through (C).

(A) Other Sections. All grounding conductors for amateur transmitting and
receiving stations shall comply with 810.21(A) through (J).

(B) Size of Protective Grounding Conductor. The protective grounding
conductor for transmitting stations shall be as large as the lead-in but not
smaller than 10 AWG copper, bronze, or copper-clad steel.

(C) Size of Operating Grounding Conductor. The operating grounding conductor
for transmitting stations shall not be less than 14 AWG copper or its
equivalent."

and Article 810.15, which states

"810.15 Grounding.

"Masts and metal structures supporting antennas shall be grounded in
accordance with 810.21."

finally, 810.21, which states

"810.21 Grounding Conductors - Receiving Stations.

Grounding conductors shall comply with 810.21(A) through (J).

(A) Material. The grounding conductor shall be of copper, aluminum,
copper-clad steel, bronze, or similar corrosion-resistant material. Aluminum
or copper-clad aluminum grounding conductors shall not be used where in
direct contact with masonry or the earth or where subject to corrosive
conditions. Where used outside, aluminum or copper-clad aluminum shall not
be installed within 450 mm (18 in.) of the earth.

(B) Insulation. Insulation on grounding conductors shall not be required.

(C) Supports. The grounding conductors shall be securely fastened in place
and shall be permitted to be directly attached to the surface wired over
without the use of insulating supports.

Exception: Where proper support cannot be provided, the size of the
grounding conductors shall be increased proportionately.

(D) Mechanical Protection. The grounding conductor shall be protected where
exposed to physical damage, or the size of the grounding conductors shall be
increased proportionately to compensate for the lack of protection. Where
the grounding conductor is run in a metal raceway, both ends of the raceway
shall be bonded to the grounding conductor or to the same terminal or
electrode to which the grounding conductor is connected.

(E) Run in Straight Line. The grounding conductor for an antenna mast or
antenna discharge unit shall be run in as straight a line as practicable
from the mast or discharge unit to the grounding electrode.
/clipped

73,
Jack Painter
Virginia Beach VA

Here is a quote from your previous post where the discussion was about
the tower and lines carrying strike current.

Jack Painter

First, a strike termination device is placed higher than other
equipment with its own down conductor.

Your reply when questioned about placing a down conductor in parallel
with the tower was:
I never suggested such a silly thing! You mistake an earlier reference I made to a bonding conductor.

As far as down conductors go you need to read farther to see what they
are using them for. We are talking about towers here. No down
conductors needed. If you are talking about a building or wooden pole
mounted antenna then that's a different story.

The applications of grounding and bonding principles are not reserved
for an elite society of engineers and electricians as you might like
to think. They are free and available to all. There are no secrets
involved.
Quoting a load of authoritative directives is not a substitute for
understanding.

It is a play of semantics when you say " an important distinction to
understand the difference between bonding and grounding". I would
guess that it does not take too much study to understand that real
ground can not be half way up a tower. So whether you are "bonding" or
"grounding" a cable on a tower, the end result is unmistakably the
same.

It seems that some of the discontinuity may come from lack of basic
understanding of RF principles. Lightning is not just a direct current
event that requires only consideration for high currents.

As far as buried cables go:
I will ask the same question again that you avoided from last time but
instead provided mounds of quotes that do not address the point.

"Do you think that you can bury the feed wire for your long wire
antenna and have it work very well? What do you think will happen to
the RF on it? Will it make it all the way back to your receiver the
same as it would if it were above ground?"

This is a very relevant to "buried coax lines".

73
Gary K4FMX

"Gary Schafer" wrote

Here is a quote from your previous post where the discussion was about
the tower and lines carrying strike current.

Jack Painter

First, a strike termination device is placed higher than other
equipment with its own down conductor.

Your reply when questioned about placing a down conductor in parallel
with the tower was:
I never suggested such a silly thing! You mistake an earlier reference I
made to a bonding conductor.

You're displaying dimensia Gary. You accused me of suggesting a #6 wire
would be useful as a down conductor and I never said such a ridiculous
thing. You misread the posts, or still don't understand most of the
terminology that the entire electrical, fire protection, lightning
protection and communication industry use to refer to bonding and grounding
components.

in news:qBdod.15535$D26.3848@lakeread03... I said, and I quote:
"Burying a grounding electrode conductor is normally a code requirement. But
that is not what you have in connecting the tower ground system to the
station ground, AC mains ground, etc. Those are bonding conductors, and they
are in many cases required to be insulated. Not in this case, but I want you
to understand the difference between grounding, voltage division from many
grounds, and a bonding conductor between your station and the tower. The
latter is to maintain equipotential, and will not carry more than just
equalizing currents. It will be well within the capability of a #6 insulated
wire, should you choose to use that."

I'm not being condescending, if you're still confused there please say so,
and I will try to explain it better.

As far as down conductors go you need to read farther to see what they
are using them for. We are talking about towers here. No down
conductors needed. If you are talking about a building or wooden pole
mounted antenna then that's a different story.

Its clear to me who needs to do the reading here. Your last shot was also
wide of the mark regarding down conductors on towers. They are used on
communication towers in exactly the same fashion as they are on any
structure, to provide a dedicated path to a grounding electrode for the
charge received by a strike termination device. A tower down conductor is
bonded to the tower frames in many places, that's the same as a down
conductor on any structure is bonded to metal stairways, handrails, roof
flashing, etc. on its way to ground.


The applications of grounding and bonding principles are not reserved
for an elite society of engineers and electricians as you might like
to think. They are free and available to all. There are no secrets
involved.

Please don't take my comments so far out of context. But you're right it is
reserved, its reserved for those who pay the fees and time to subscribe to
organizations that license the printing of the codes, and constantly discuss
and explain changes, applications and plan future requirement for them.

Quoting a load of authoritative directives is not a substitute for
understanding.

It is a play of semantics when you say " an important distinction to
understand the difference between bonding and grounding". I would
guess that it does not take too much study to understand that real
ground can not be half way up a tower. So whether you are "bonding" or
"grounding" a cable on a tower, the end result is unmistakably the
same.

Neither should it be as oversimplified as your rebuttal. They are not the
same thing and to misunderstand it would be to make deadly mistakes when
applying those principles, both outside and inside structures where external
equipments connect to people.


It seems that some of the discontinuity may come from lack of basic
understanding of RF principles. Lightning is not just a direct current
event that requires only consideration for high currents.


This is a subterfuge to divert the attention from the basics we were
discussing, and until that is resolved there is no room for discussion about
protection design based on frequencies of structures and wiring in the near
field, or the AC components of lightning.

As far as buried cables go:
I will ask the same question again that you avoided from last time but
instead provided mounds of quotes that do not address the point.

"Do you think that you can bury the feed wire for your long wire
antenna and have it work very well? What do you think will happen to
the RF on it? Will it make it all the way back to your receiver the
same as it would if it were above ground?"

This is a very relevant to "buried coax lines".

I ignored that question because I thought it had no relevance to anything
here. Maybe you can rephrase what you are asking please? We are talking
about shielded coax, and the relationship between lightning and the thin
outer covering of coax, the coax shield, the inside dialectric, and the
center conductor are quite unique and not convertible to a relationship with
bare wire feed of some long wire. My coax feedlines are buried - so I don't
hit them with the lawn mower! But it doesn't mean anything to lightning to
have your coax buried, unless you hire a trencher to sink them deeper than
the ground rods. In a near field strike there will be massive and
sufficient energy to make all that shield grounding, bonding and placement
of arrestors real important. And it won't matter where the coax is if all of
those requirements are not met. if you think your coax is protected under
your lawn, lay some turf over your radios and protect them the same way.
It's a wives tale Gary, just like so many RF-wives tales, only there are
more capable folks here to dispel those.

73,
Jack Painter
Virginia Beach VA

On Tue, 23 Nov 2004 17:42:24 -0500, "Jack Painter"
wrote:


"Gary Schafer" wrote

Here is a quote from your previous post where the discussion was about
the tower and lines carrying strike current.

Jack Painter

First, a strike termination device is placed higher than other
equipment with its own down conductor.

Your reply when questioned about placing a down conductor in parallel
with the tower was:
I never suggested such a silly thing! You mistake an earlier reference I
made to a bonding conductor.

You're displaying dimensia Gary. You accused me of suggesting a #6 wire
would be useful as a down conductor and I never said such a ridiculous
thing. You misread the posts, or still don't understand most of the
terminology that the entire electrical, fire protection, lightning
protection and communication industry use to refer to bonding and grounding
components.

Jack, my apologies. You did not suggest a #6 down conductor on such a
tower as I reread your original post. But you did suggest a down
conductor on the tower, you just didn't mention the size.


in news:qBdod.15535$D26.3848@lakeread03... I said, and I quote:
"Burying a grounding electrode conductor is normally a code requirement. But
that is not what you have in connecting the tower ground system to the
station ground, AC mains ground, etc. Those are bonding conductors, and they
are in many cases required to be insulated. Not in this case, but I want you
to understand the difference between grounding, voltage division from many
grounds, and a bonding conductor between your station and the tower. The
latter is to maintain equipotential, and will not carry more than just
equalizing currents. It will be well within the capability of a #6 insulated
wire, should you choose to use that."

I'm not being condescending, if you're still confused there please say so,
and I will try to explain it better.

As far as down conductors go you need to read farther to see what they
are using them for. We are talking about towers here. No down
conductors needed. If you are talking about a building or wooden pole
mounted antenna then that's a different story.

Its clear to me who needs to do the reading here. Your last shot was also
wide of the mark regarding down conductors on towers. They are used on
communication towers in exactly the same fashion as they are on any
structure, to provide a dedicated path to a grounding electrode for the
charge received by a strike termination device. A tower down conductor is
bonded to the tower frames in many places, that's the same as a down
conductor on any structure is bonded to metal stairways, handrails, roof
flashing, etc. on its way to ground.

DOWN CONDUCTOR ON A BUILDING:
A down conductor on a building is a whole different deal than on a
tower. On a building the "metal stairways, handrails, roof flashing,
etc." are bonded to prevent flashovers as the down conductor runs by.
The down conductor is run because there is no better path to connect
to.

DOWN CONDUCTOR ON A TOWER:
My comments about a down conductor on a tower were based around the
fact that a down conductor on such a tower is useless. Tower joints
should be bonded to negate any resistance in the joints but a down
conductor the length of the tower is a waste of wire. I was trying to
point out that any down conductor, coax cables or anything else
running down the tower, including the tower, would all share the
lightning energy. It is impossible to isolate any part.

The fact that a typical tower has so much mass, and as a result much
lower inductance, in comparison to any down conductor that you could
hang on the tower negates it's usefulness.

And yes, I know that some people do install down conductors on towers.
Some people also hang pointy dissipation arrays on the top of their
tower too.

Some engineers and "communications managers" specify them also. Hams
don't have a lock on ignorance in this department.



The applications of grounding and bonding principles are not reserved
for an elite society of engineers and electricians as you might like
to think. They are free and available to all. There are no secrets
involved.

Please don't take my comments so far out of context. But you're right it is
reserved, its reserved for those who pay the fees and time to subscribe to
organizations that license the printing of the codes, and constantly discuss
and explain changes, applications and plan future requirement for them.

I would guess then that the general library is also "reserved".


Quoting a load of authoritative directives is not a substitute for
understanding.

It is a play of semantics when you say " an important distinction to
understand the difference between bonding and grounding". I would
guess that it does not take too much study to understand that real
ground can not be half way up a tower. So whether you are "bonding" or
"grounding" a cable on a tower, the end result is unmistakably the
same.

Neither should it be as oversimplified as your rebuttal. They are not the
same thing and to misunderstand it would be to make deadly mistakes when
applying those principles, both outside and inside structures where external
equipments connect to people.

They are the same thing when we are talking about bonding or grounding
on the tower itself, which is where that discussion spawned from.
When you start jumping to other subjects then they may or may not be
the same thing.
Sometimes it is difficult to tell what you are discussing as you want
to throw so many things into the fire.



It seems that some of the discontinuity may come from lack of basic
understanding of RF principles. Lightning is not just a direct current
event that requires only consideration for high currents.


This is a subterfuge to divert the attention from the basics we were
discussing, and until that is resolved there is no room for discussion about
protection design based on frequencies of structures and wiring in the near
field, or the AC components of lightning.

No diversion intended. Only a notice to read the other side of the
page.
I thought we were discussing lightning strike dissipation and
preventing it from reaching the shack. How can you ignore the AC
components? They are a major part of it.


As far as buried cables go:
I will ask the same question again that you avoided from last time but
instead provided mounds of quotes that do not address the point.

"Do you think that you can bury the feed wire for your long wire
antenna and have it work very well? What do you think will happen to
the RF on it? Will it make it all the way back to your receiver the
same as it would if it were above ground?"

This is a very relevant to "buried coax lines".

I ignored that question because I thought it had no relevance to anything
here. Maybe you can rephrase what you are asking please? We are talking
about shielded coax, and the relationship between lightning and the thin
outer covering of coax, the coax shield, the inside dialectric, and the
center conductor are quite unique and not convertible to a relationship with
bare wire feed of some long wire. My coax feedlines are buried - so I don't
hit them with the lawn mower! But it doesn't mean anything to lightning to
have your coax buried, unless you hire a trencher to sink them deeper than
the ground rods. In a near field strike there will be massive and
sufficient energy to make all that shield grounding, bonding and placement
of arrestors real important. And it won't matter where the coax is if all of
those requirements are not met. if you think your coax is protected under
your lawn, lay some turf over your radios and protect them the same way.
It's a wives tale Gary, just like so many RF-wives tales, only there are
more capable folks here to dispel those.


BURIED COAX:
The relevance here was explained in my first post on the subject.
Let's try again. I asked if you thought that if you buried the feed
wire from your long wire antenna, it can be insulated if you choose
but a single wire, if you would get as much signal from your antenna
to your receiver as you would if that same feed wire was not buried
but run in the air away from ground. What do you think would happen to
the RF on that feed wire? Do you think that it would go unattenuated
the same as it would if the wire was in the air? Or would you loose
most of the signal if it were buried?

This is relevant to burying the coax lines coming off a tower and
leading into your shack. The coax shield will be carrying large
amounts of lightning energy during a strike that it receives when the
top of the tower is struck. Even though the coax is grounded at the
base of the tower. since there is no perfect ground system you are not
going to be able to dump all the energy to the tower ground.

For the moment forget about possible induced currents into the cable
itself from nearby strikes etc.

73
Gary K4FMX

73,
Jack Painter
Virginia Beach VA

"Gary Schafer" wrote

Jack, my apologies. You did not suggest a #6 down conductor on such a
tower as I reread your original post. But you did suggest a down
conductor on the tower, you just didn't mention the size.

O.k. Gary. And I didn't mean to suggest a down conductor on a tower either,
as its true there is little evidence that it carries more than 25-30% of the
total energy with the tower carrying the balance. But it sure is specified
in a LOT of places. I follow specifications to the letter unless there is
clear evidence that in my particular facility it could be harmful or
counterproductive.

DOWN CONDUCTOR ON A BUILDING:
A down conductor on a building is a whole different deal than on a
tower. On a building the "metal stairways, handrails, roof flashing,
etc." are bonded to prevent flashovers as the down conductor runs by.
The down conductor is run because there is no better path to connect
to.

DOWN CONDUCTOR ON A TOWER:
My comments about a down conductor on a tower were based around the
fact that a down conductor on such a tower is useless. Tower joints
should be bonded to negate any resistance in the joints but a down
conductor the length of the tower is a waste of wire. I was trying to
point out that any down conductor, coax cables or anything else
running down the tower, including the tower, would all share the
lightning energy. It is impossible to isolate any part.

The odd system or two specifies isolated tower down conductors. A majority
proscribe down conductors and bonding the entire length, and another small
percentage use an air terminal but bond it directly to to the tower legs and
eliminate the down conductor. Please don't use PolyPhaser's toy lightning
machine antics as evidence there. Big industry and government spend millions
bringing rocket-triggered lightning down towers all the time, and if down
conductors are still being specified they must help. How much, and if it
applies to a typical ham tower, let the user decide I guess.


The fact that a typical tower has so much mass, and as a result much
lower inductance, in comparison to any down conductor that you could
hang on the tower negates it's usefulness.

And yes, I know that some people do install down conductors on towers.
Some people also hang pointy dissipation arrays on the top of their
tower too.

Some engineers and "communications managers" specify them also. Hams
don't have a lock on ignorance in this department.

That's true, but maybe 25-30% of the energy directed on a faster path via
down conductor means something, I have not seen why. The ESE Dissipaters
however - another ball of ceiling wax and snake oil. Throughly disproven yet
to this minute it ties up the Lightning Standards Group of the IEEE while
they fight over the language to discredit it with. There is also at least
one insurance company that discounts for use of the CTS (Charge Transfer
System). There is no reliable science behind this theory but it hangs on...

Please don't take my comments so far out of context. But you're right it
is
reserved, its reserved for those who pay the fees and time to subscribe
to
organizations that license the printing of the codes, and constantly
discuss
and explain changes, applications and plan future requirement for them.

I would guess then that the general library is also "reserved".

A good library might have at least the NEC-70 (Electrical code). You can buy
the NFPA-780 Standard for the Installation of Lightning Protection Systems
for about $40 from NFPA directly. The October 2004 edition is the latest.
The full NEC-70 is a lot more.

Sometimes it is difficult to tell what you are discussing as you want
to throw so many things into the fire.

Roger that, sorry. My brain is awash with this stuff but it has been the
most productive, interesting and generally most fun project I have taken on
in years.

I thought we were discussing lightning strike dissipation and
preventing it from reaching the shack. How can you ignore the AC
components? They are a major part of it.

I think we were trying to answer a posters question about grounding the coax
shield before it meets an arrestor, yes.

BURIED COAX:
The relevance here was explained in my first post on the subject.
Let's try again. I asked if you thought that if you buried the feed
wire from your long wire antenna, it can be insulated if you choose
but a single wire, if you would get as much signal from your antenna
to your receiver as you would if that same feed wire was not buried
but run in the air away from ground. What do you think would happen to
the RF on that feed wire? Do you think that it would go unattenuated
the same as it would if the wire was in the air? Or would you loose
most of the signal if it were buried?

This is relevant to burying the coax lines coming off a tower and
leading into your shack. The coax shield will be carrying large
amounts of lightning energy during a strike that it receives when the
top of the tower is struck. Even though the coax is grounded at the
base of the tower. since there is no perfect ground system you are not
going to be able to dump all the energy to the tower ground.

For the moment forget about possible induced currents into the cable
itself from nearby strikes etc.

Lets come back to that then, because it would require DEEP burying to avoid
(It is commonly avoided by shield grounding, arrestors, grounded steel
conduit, geometry, and distance). Anyway, yes, there would be some
attenuation from a cheap wire insulator that was not designed to prevent RF
from travel in either direction. But 95% or greater coax shielding with its
dialectric inner liner is designed to keep RF from penetrating. While it
allows travel on its inner and outer shield covers during some oddities of
RF behavior, it does not allow attenuation of the RF signal by design. Then
lets agree it's designed to be 50ohm, or 60ohm, if you want to use the anal
British system (which we know is actually correct there Limeys). So if the
point you were making was just that some inductance from earth is felt (even
on coax) - I can't disagree, but neither would this wildly high impedance to
even wet earth impress lightning in the least bit. In dry soil it would be
invisible for all practical purposes. After all we stress the need to ground
(via 8-10' of copper electrode) the coax shield (and the center conductor
via arrestors) so what good is insulated earth? That was my point, and
unless you count on unprotected coax breaking-down and arcing into the earth
along its length, the burying part is just a no-gain event (just like a
tower downcomductor???) Substantially all of the energy from a tower or
antenna strike is already on the coax and it's first arrestor, top-shield
bond, (middle shield bond if you like) and tower bottom shield ground (and
another arrestor if you like) at the same time. Its even on the GROUND at
the same time. They all rise in near unison within about 5 microseconds and
fall in potential within 20-40 micro seconds. Where damage usually occurs
is when unprotected coax has a distant ground only, and the voltage remains
high its entire length as a result. This is where I believe you might tempt
the voltage out anywhere along a buried path, maybe in thousands of little
holes. It could just as easily happen laying on the ground though, so I fail
to see what surrounding it in dirt can do. Apparently so do engineers who
specify controls and installation procedures. That doesn't mean your
argument can't be a good one. I just don't see it as that yet.

73,
Jack Painter
Virginia Beach VA