On Tue, 23 Nov 2004 11:27:03 +0000 (UTC), "Reg Edwards"
wrote:

Just another thought -

If a resourceful ham has no rubber boots he can always stand on one leg and
hop.
---
Reg


Hams seem to be resourceful don't they! :)

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

One last note on down conductors. You can figure out what the
inductance of a particular gauge of wire is. You can also figure out
what the inductance of a particular size tower is. Just looking at the
size difference you can see that the inductance of the small wire in
comparison to the tower will be many times greater. That equates the
many times greater voltage drop on the small wire. I would say that
carrying 25% to 30% of the total current would be way optimistic. It
is not just the gauge of the wire verses the gauge of the tower legs
but how much inductance each presents. The cross section area of the
face of the tower makes for less inductance as well as the size of the
legs.

RADIALS
Buried radials make an excellent lightning ground system. An AM
broadcast tower ground system is an example. Not only is it an
excellent Radio ground but it is also an excellent lightning ground.

Running radials out from the base of a tower that you want to ground
is a big plus in addition to ground rods I think you will have to
agree.

It is suggested that many shorter radials be used rather than a few
long ones in a lightning ground system. The reason is that the
inductance gets too high to do much good as the length gets long.

Also long ground rods suffer the same fate. Too long and the
inductance is so high. That is one reason why additional shorter rods
are recommended rather than very long rods.

COAX LINES
Only talking about the energy on the OUTER SHIELD of coax here now.
With buried coax lines coming from the tower they serve the same as a
radial tied to the tower. They will dissipate some of the energy just
the same as a radial will. And they do not have to be bare copper
shield lines to do so either.

This was where I was going with the buried insulated single wire long
wire lead.

By the time the energy on the shield of the cable reaches the shack,
part of it has dissipated by the coupling to earth. Also the impedance
seen at that end is much higher than it is at the tower end of the
coax.
Just like the radial. The ground is a choke if you will.
Add ferite beads on a transmission line and you greatly limit the
amount of RF current that gets past on the shield. That is what the
earth does to the coax line buried.

73
Gary K4FMX

RADIALS
It is suggested that many shorter radials be used rather than a few
long ones in a lightning ground system. The reason is that the
inductance gets too high to do much good as the length gets long.

50' is the number generally used as the longest effective run of an
individual radial arm for lightning protection.


Also long ground rods suffer the same fate. Too long and the
inductance is so high. That is one reason why additional shorter rods
are recommended rather than very long rods.

Up to 100' lengths of 1" copper clad steel ground rod are often sunk in
order to obtain 25 ohm resistance. 5 ohm would be better but some soil
condtions (such as dry sand) may be 1000 ohms. Bentonite and other similar
soil-conditioners cannot be used effectively in sand, that is unless they
occupy a deep 3' diameter hole. Here's an interesting anamoly in the NEC,
which requires grounding electrode resistance to be 25 ohm at the service
entrance ground. If that cannot be accomplished, then a second ground
electrode must be used. But there is no requirement to test the results
after the second grounding electrode is added! It could easily be 400 ohms
after two rods sunk in terrible soil, and yet it meets the code. There are
few such glaring examples of short sightedness in the NEC, but engineers and
contractors both have to be aware of these problems to design and build safe
lightning protection systems.

According to both NEC and NFPA, the first grounding electrode coming off a
structure may be shorter if conditions require, but then must be followed
with a second electrode no shorter than 8' long and sunk to a depth of 10'.
This is brand new in the 2004 edition btw. The minimum 8' long rod sunk to
depth of 10' remains the code *minimum* in all other standards and
applications where grounding electrodes are required. Distance between
electrodes should be not less than sum of both their lengths. O.K. there is
another little anamoly, since this does not take into account having to
reach down 100' to find low resistance ground! Of course UFER grounds are
also well accepted and commonly specified. This relates to another FAVORITE
wives tale of hams, that is that tower foundations will explode if the
grounding system goes into its concrete. There is not one documented case of
this happening, yet the fable continues. It's true masonry and lightning do
not get along well at all, but bonded conductors inside concrete foundations
make it an excellent grounding system. It has been used world wide for
decades.


COAX LINES
Only talking about the energy on the OUTER SHIELD of coax here now.
With buried coax lines coming from the tower they serve the same as a
radial tied to the tower. They will dissipate some of the energy just
the same as a radial will. And they do not have to be bare copper
shield lines to do so either.

This was where I was going with the buried insulated single wire long
wire lead.

We do now agree with where you were going. But I hope I can show you it's
not a place you want to hold any faith in protecting equipment with.

By the time the energy on the shield of the cable reaches the shack,
part of it has dissipated by the coupling to earth. Also the impedance
seen at that end is much higher than it is at the tower end of the
coax.
Just like the radial. The ground is a choke if you will.
Add ferite beads on a transmission line and you greatly limit the
amount of RF current that gets past on the shield. That is what the
earth does to the coax line buried.

I understand what you are saying, thanks. Lets leave the ferrites alone
though, because they can't shunt energy into dirt that doesn't have them,
and if this was effective for lightning protection we would all use
ferrite-shielded coax, right?

Back to the coax shield now - are you aware what is the most voltage that
standard coax can carry? It's about 5,500v. At close to 4,500v coax
dielectric breaks down and inner and outer conductors become "one". Close to
5,500v, the outer insulator of coax fails (similar to house wiring at
6,000v). Above breakdown voltage there will be flashovers to any object of
lower potential, including the air in some cases. At anything less than
breakdown voltage, you could hold the coax in a gloved hand and not feel
anything. And neither would the earth, if that's where it was laying.

Let's review: It does not matter one bit whether you bleed off some RF
energy out of a coax underground, because up to 5,500v of DC energy is going
to get through with absolutely no affect from being near the dirt. And at
over 6,000v nothing is going anywhere through that coax any more, it has
reached breakdown and arcs over, melting and expelling the remains of its
conductive materials all over the place. I have several such samples in my
collection btw.

Finally, this will conclude my points about not burying coax for lightning
protection:
Unless coax feedlines are protected by shield grounding and lightning surge
protection devices in the proper manner and locations, there is no hope for
its survival in even a nearby strike, let alone a direct attachment. If they
are properly protected, it does not improve this protection to bury them.
Perhaps it would increase the longevity of some surge protection devices and
arrestors by limiting some RF energy they would otherwise be presented with.
You would have to ask them that question. I have never seen a manufacturer
of these devices require feedlines be buried, maybe they are missing this
too. They do however require the devices we have talked about.

It's of course fine if you want to hide coax, possibly reducing some
external RF affects *and* the manufacturer says it is designed for below
frost-line burying. Mine are buried too.

73 AND HAPPY THANKSGIVING

Jack Painter
Virginia Beach VA

On Wed, 24 Nov 2004 18:40:41 -0500, "Jack Painter"
wrote:

RADIALS
It is suggested that many shorter radials be used rather than a few
long ones in a lightning ground system. The reason is that the
inductance gets too high to do much good as the length gets long.

50' is the number generally used as the longest effective run of an
individual radial arm for lightning protection.


Also long ground rods suffer the same fate. Too long and the
inductance is so high. That is one reason why additional shorter rods
are recommended rather than very long rods.

Up to 100' lengths of 1" copper clad steel ground rod are often sunk in
order to obtain 25 ohm resistance.

Those kind of lengths are only "last resort" ground systems if there
is no other possible way to get any sort of ground. The inductance
will be so high on that length that it will do little for lightning.

5 ohm would be better but some soil
condtions (such as dry sand) may be 1000 ohms. Bentonite and other similar
soil-conditioners cannot be used effectively in sand, that is unless they
occupy a deep 3' diameter hole. Here's an interesting anamoly in the NEC,
which requires grounding electrode resistance to be 25 ohm at the service
entrance ground. If that cannot be accomplished, then a second ground
electrode must be used. But there is no requirement to test the results
after the second grounding electrode is added! It could easily be 400 ohms
after two rods sunk in terrible soil, and yet it meets the code. There are
few such glaring examples of short sightedness in the NEC, but engineers and
contractors both have to be aware of these problems to design and build safe
lightning protection systems.

According to both NEC and NFPA, the first grounding electrode coming off a
structure may be shorter if conditions require, but then must be followed
with a second electrode no shorter than 8' long and sunk to a depth of 10'.
This is brand new in the 2004 edition btw. The minimum 8' long rod sunk to
depth of 10' remains the code *minimum* in all other standards and
applications where grounding electrodes are required. Distance between
electrodes should be not less than sum of both their lengths. O.K. there is
another little anamoly, since this does not take into account having to
reach down 100' to find low resistance ground! Of course UFER grounds are
also well accepted and commonly specified. This relates to another FAVORITE
wives tale of hams, that is that tower foundations will explode if the
grounding system goes into its concrete. There is not one documented case of
this happening, yet the fable continues. It's true masonry and lightning do
not get along well at all, but bonded conductors inside concrete foundations
make it an excellent grounding system. It has been used world wide for
decades.

Unfortunately it is not just an old wives tale. Over the years I have
seen several tower bases cracked or exploded chunks out of them from
lightning strikes.

To effectively use the tower concrete as a ground is a good thing to
do. However it must never be the only ground. Ground rods also need to
be installed and connected to the tower or you will have the effects
that I have witnessed. The ones that I saw did not have any auxiliary
ground connections.



COAX LINES
Only talking about the energy on the OUTER SHIELD of coax here now.
With buried coax lines coming from the tower they serve the same as a
radial tied to the tower. They will dissipate some of the energy just
the same as a radial will. And they do not have to be bare copper
shield lines to do so either.

This was where I was going with the buried insulated single wire long
wire lead.

We do now agree with where you were going. But I hope I can show you it's
not a place you want to hold any faith in protecting equipment with.

By the time the energy on the shield of the cable reaches the shack,
part of it has dissipated by the coupling to earth. Also the impedance
seen at that end is much higher than it is at the tower end of the
coax.
Just like the radial. The ground is a choke if you will.
Add ferite beads on a transmission line and you greatly limit the
amount of RF current that gets past on the shield. That is what the
earth does to the coax line buried.

I understand what you are saying, thanks. Lets leave the ferrites alone
though, because they can't shunt energy into dirt that doesn't have them,
and if this was effective for lightning protection we would all use
ferrite-shielded coax, right?

Back to the coax shield now - are you aware what is the most voltage that
standard coax can carry? It's about 5,500v. At close to 4,500v coax
dielectric breaks down and inner and outer conductors become "one". Close to
5,500v, the outer insulator of coax fails (similar to house wiring at
6,000v). Above breakdown voltage there will be flashovers to any object of
lower potential, including the air in some cases. At anything less than
breakdown voltage, you could hold the coax in a gloved hand and not feel
anything. And neither would the earth, if that's where it was laying.

Let's review: It does not matter one bit whether you bleed off some RF
energy out of a coax underground, because up to 5,500v of DC energy is going
to get through with absolutely no affect from being near the dirt. And at
over 6,000v nothing is going anywhere through that coax any more, it has
reached breakdown and arcs over, melting and expelling the remains of its
conductive materials all over the place. I have several such samples in my
collection btw.

Finally, this will conclude my points about not burying coax for lightning
protection:
Unless coax feedlines are protected by shield grounding and lightning surge
protection devices in the proper manner and locations, there is no hope for
its survival in even a nearby strike, let alone a direct attachment. If they
are properly protected, it does not improve this protection to bury them.
Perhaps it would increase the longevity of some surge protection devices and
arrestors by limiting some RF energy they would otherwise be presented with.
You would have to ask them that question. I have never seen a manufacturer
of these devices require feedlines be buried, maybe they are missing this
too. They do however require the devices we have talked about.

Well now, what if the DC component of the strike is only 5495 volts?
Still useless to remove most of the RF component of the strike? The RF
part does contain significant energy you know. After all isn't the
whole idea here to keep as much energy out of the shack as possible?
The DC part of the strike is usually easier to suppress with a ground
connection. The AC part is dependent on the inductance of the
conductor to get it to ground. Why not use all available means at
hand.

Jack, without trying to sound sarcastic I would recommend that you do
some reading about transmission line theory . Also some basics on
inductance and capacitance and how energy is transferred in their
fields. Outside of what the lightning protection people publish. These
may help you in your quest to become a lightning guru. It is fine to
read all the specifications of the NEC and other agencies that write
specs. But you need to remember that they are using one glove size to
try and fit all. If you understand a little more about how things work
you can come up with your own fixes to fit the situation much better.
You obviously have an appetite for this stuff. Spend a little time on
the theory side.
You have to be able to adapt to and use the surroundings available to
best advantage. The perfect system can not always be built.

Well I think I have had my run on this thread.

Best Holidays
Gary K4FMX


It's of course fine if you want to hide coax, possibly reducing some
external RF affects *and* the manufacturer says it is designed for below
frost-line burying. Mine are buried too.

73 AND HAPPY THANKSGIVING

Jack Painter
Virginia Beach VA