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