On 29 Nov 2003 02:35:22 -0800, (Mark Keith) wrote:

(K9SQG) wrote in message ...
That is not a wise idea. If your mast takes a direct hit, or if there is one
nearby, there is a possibility that some of the energy will go into the house
via that ground rod. Antenna grounds should always be isolated from
housewiring grounds.


If all grounds are at the same potential, no current can flow between them.
Not to mention the NEC requires it in the U.S. MK

When you figure the rise time there can easily be several thousand
volts between the base of the antenna mast and the electrical system
ground. IE the voltage could be 50,000 at the tower and not even have
started to rise at the electrical ground.

It's not just a simple CD circuit.
I've seen tower strikes where there was such a strong current and fast
rise time, the magnetic field quenched the current flow and the
lightening got off part way down and jumped sideways to something
else.

You'll have to fix the return add due to dumb virus checkers, not spam
Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair?)
www.rogerhalstead.com

Roger Halstead wrote in message . ..
On 29 Nov 2003 02:35:22 -0800, (Mark Keith) wrote:

(K9SQG) wrote in message ...
That is not a wise idea. If your mast takes a direct hit, or if there is one
nearby, there is a possibility that some of the energy will go into the house
via that ground rod. Antenna grounds should always be isolated from
housewiring grounds.


If all grounds are at the same potential, no current can flow between them.
Not to mention the NEC requires it in the U.S. MK

When you figure the rise time there can easily be several thousand
volts between the base of the antenna mast and the electrical system
ground. IE the voltage could be 50,000 at the tower and not even have
started to rise at the electrical ground.

In my case, those are pretty much the same place. All my grounds tend
to rise in potential at the same time, being they are all tied
together at the base of the mast. Nothing is perfect of course, but
you sure don't want any large potential differences between grounds.

It's not just a simple CD circuit.
I've seen tower strikes where there was such a strong current and fast
rise time, the magnetic field quenched the current flow and the
lightening got off part way down and jumped sideways to something
else.

If I remember right, the original poster was going to mount an antenna
on a roof. That has the potential for even more serious problems if
the antenna acts as a lightning rod. He'd want as few turns or sharp
bends in the ground wire to earth. This is why I much prefer using a
metal mast on the side of the house to support verticals or other high
risk antennas, rather than a mast attached to the roof of the house.
And then hoping a ground wire will safely direct the charge to
earth...It usually will, at least much better than the house itself,
but it's kind of scary if it has turns or bends.
The important part at the house is making sure that everything rises
together so there's no lower resistance path for the charge to take
through the shack or house. At the mast, I always tape all coaxes or
wires to the mast, and run them all the way down to earth to try to
avoid flashing problems. So far in two strikes to the mast, I haven't
noticed any, and I have a breaker box, elevated power lead in, phone
lines, cable lines, all within 5 ft of that mast. MK

Though in practice you are correct to express concern, your reason is
not properly stated. You further the lighting rod myth.

Actually, "if the antenna acts as a lightning rod." He'll have little
problem. The purpose of a true lightning rod is to blead off the charge,
defeating a strike, not to attract it. A lightning srtike will blow any
lightning rod system to smithereenes.
When a charged object has a sharp corner or point, the charge tends to
collect there. Because there is more charge at that p[oint it will have a
higher concentration and therefore a higher voltage. It builds to the point
of forming a corona/plasma and will discharge it. That's why the van De
Graf (sp) generators have the round ball on the top. They WANT to build up
the charge and not loose any more than necessary..
I all fairness, I do not know if lightning rod systems work in
practice.They do wear out due to the discharge corona and should be
sharpened periodically. Apparently the points of the typical beam are
not sufficient or they wouldn't get struck, no?

73, Steve K,9.D;C;I


"Mark Keith" wrote in message
om...
Roger Halstead wrote in message
. ..
On 29 Nov 2003 02:35:22 -0800, (Mark Keith) wrote:

(K9SQG) wrote in message
...
That is not a wise idea. If your mast takes a direct hit, or if
there is one
nearby, there is a possibility that some of the energy will go into
the house
via that ground rod. Antenna grounds should always be isolated from
housewiring grounds.


If all grounds are at the same potential, no current can flow between
them.
Not to mention the NEC requires it in the U.S. MK

When you figure the rise time there can easily be several thousand
volts between the base of the antenna mast and the electrical system
ground. IE the voltage could be 50,000 at the tower and not even have
started to rise at the electrical ground.

In my case, those are pretty much the same place. All my grounds tend
to rise in potential at the same time, being they are all tied
together at the base of the mast. Nothing is perfect of course, but
you sure don't want any large potential differences between grounds.

It's not just a simple CD circuit.
I've seen tower strikes where there was such a strong current and fast
rise time, the magnetic field quenched the current flow and the
lightening got off part way down and jumped sideways to something
else.

If I remember right, the original poster was going to mount an antenna
on a roof. That has the potential for even more serious problems if
the antenna acts as a lightning rod. He'd want as few turns or sharp
bends in the ground wire to earth. This is why I much prefer using a
metal mast on the side of the house to support verticals or other high
risk antennas, rather than a mast attached to the roof of the house.
And then hoping a ground wire will safely direct the charge to
earth...It usually will, at least much better than the house itself,
but it's kind of scary if it has turns or bends.
The important part at the house is making sure that everything rises
together so there's no lower resistance path for the charge to take
through the shack or house. At the mast, I always tape all coaxes or
wires to the mast, and run them all the way down to earth to try to
avoid flashing problems. So far in two strikes to the mast, I haven't
noticed any, and I have a breaker box, elevated power lead in, phone
lines, cable lines, all within 5 ft of that mast. MK

Steve,

Sorry, you are the one who is furthering the lightning rod myth. There is no way
a "true lightning rod" bleeds off enough charge to avoid a strike. That idea
is about 99% urban legend.

I suggest perusal of the Polyphaser web site. There is a lot of good information
there. One relevant comment is:

"The real solution for lightning protection is to have control of the strike
energy. To do this, a well-designed ground system will be a better investment
than cluttering up the top of the tower."

The cluttering refers to a bottlebrush arrangement of multiple sharp points, but
the same idea applies to a single sharp point.

As usual, Mark is right on target.

73,
Gene, W4SZ

Steve Nosko wrote:
Though in practice you are correct to express concern, your reason is
not properly stated. You further the lighting rod myth.

Actually, "if the antenna acts as a lightning rod." He'll have little
problem. The purpose of a true lightning rod is to blead off the charge,
defeating a strike, not to attract it. A lightning srtike will blow any
lightning rod system to smithereenes.
When a charged object has a sharp corner or point, the charge tends to
collect there. Because there is more charge at that p[oint it will have a
higher concentration and therefore a higher voltage. It builds to the point
of forming a corona/plasma and will discharge it. That's why the van De
Graf (sp) generators have the round ball on the top. They WANT to build up
the charge and not loose any more than necessary..
I all fairness, I do not know if lightning rod systems work in
practice.They do wear out due to the discharge corona and should be
sharpened periodically. Apparently the points of the typical beam are
not sufficient or they wouldn't get struck, no?

73, Steve K,9.D;C;I


"Mark Keith" wrote in message

In my case, those are pretty much the same place. All my grounds tend
to rise in potential at the same time, being they are all tied
together at the base of the mast. Nothing is perfect of course, but
you sure don't want any large potential differences between grounds.

It's not just a simple CD circuit.
I've seen tower strikes where there was such a strong current and fast
rise time, the magnetic field quenched the current flow and the
lightening got off part way down and jumped sideways to something
else.

If I remember right, the original poster was going to mount an antenna
on a roof. That has the potential for even more serious problems if
the antenna acts as a lightning rod. He'd want as few turns or sharp
bends in the ground wire to earth. This is why I much prefer using a
metal mast on the side of the house to support verticals or other high
risk antennas, rather than a mast attached to the roof of the house.
And then hoping a ground wire will safely direct the charge to
earth...It usually will, at least much better than the house itself,
but it's kind of scary if it has turns or bends.
The important part at the house is making sure that everything rises
together so there's no lower resistance path for the charge to take
through the shack or house. At the mast, I always tape all coaxes or
wires to the mast, and run them all the way down to earth to try to
avoid flashing problems. So far in two strikes to the mast, I haven't
noticed any, and I have a breaker box, elevated power lead in, phone
lines, cable lines, all within 5 ft of that mast. MK

On Wed, 03 Dec 2003 19:56:06 GMT, Gene Fuller
wrote:

Steve,

Sorry, you are the one who is furthering the lightning rod myth. There is no way
a "true lightning rod" bleeds off enough charge to avoid a strike. That idea
is about 99% urban legend.

I suggest perusal of the Polyphaser web site. There is a lot of good information
there. One relevant comment is:

"The real solution for lightning protection is to have control of the strike
energy. To do this, a well-designed ground system will be a better investment
than cluttering up the top of the tower."


I'd be a bit careful about that statement on a site for a company who
makes their money from attempting to control the energy when
lightening strikes, rather than preventing the strike. There are two
distinct camps. The one that says the solution is to control the
strike and the other says to prevent the strike. Lightening strikes
are unpredictable in most cases, but if you have the tallest structure
around the odds are that it will get hit before lower nearby
structures.

The cluttering refers to a bottlebrush arrangement of multiple sharp points, but
the same idea applies to a single sharp point.

According to our electrical inspector it's not a myth, but I don't
know one way or another. However I do know that it would take little
to bleed a charge and a lot to control a strike. I also know that
every tall structure at the chemical company where I used to work had
lightening rods

Bleeding supposedly does just that. I prevents the charge from
building up to a potential that will help bridge the gap to the
feeders. The last class I had at work on electrical safety was pro
lightening rods AND ground systems. (as was the one for skywarn from
the NWS)

I do use polyphasers and end up replacing one every now and then. My
tower gets hit on average of three times per year. Since the tower
went up there have been no strikes to any home within about 5 lots
from me.

There haven't been any really close strikes that didn't hit the tower.
(of which I am aware). The neighbors are quick to tell me, "Man you
shouldda been home this afternoon when the lightening hit your tower".
That happened in August this year. They were really impressed and
more so in that we had no damage even to the radios which do not get
disconnected.

My antenna ground system has over 600 feet of bare #2 copper wire with
30 grounding rods, not counting the two ground rods for the house
electrical system and the one for the shop. They have separate feeds,
but as my computer network ties it all together, I'm thinking of
bonding the grounds for both services together and to the system
ground. I have visions of a lightening strike to one system and
reaching ground in the other by going through the 130 feet of cat-5
cable. There's a reason I back up everything on CDs and DVDs.

You'll have to fix the return add due to dumb virus checkers, not spam
Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair?)
www.rogerhalstead.com

snip

Roger Halstead wrote:


The cluttering refers to a bottlebrush arrangement of multiple sharp points, but
the same idea applies to a single sharp point.

According to our electrical inspector it's not a myth, but I don't
know one way or another. However I do know that it would take little
to bleed a charge and a lot to control a strike. I also know that
every tall structure at the chemical company where I used to work had
lightening rods

Bleeding supposedly does just that. I prevents the charge from
building up to a potential that will help bridge the gap to the
feeders.

I don't know if I would call it a total myth, but I call it fairly risky
none the less. I know I sure wouldn't trust one to protect me from a
strike. I don't think they can bleed the charges from constant hard wind
and rain fast enough to do any good. It's like taking a whiz in a
whirlwind.

The last class I had at work on electrical safety was pro
lightening rods AND ground systems. (as was the one for skywarn from
the NWS)

I agree there, if he is talking about the traditional pointy lightning
rod used to protect other gear or buildings. I'm of the opinion strikes
can never be totally avoided, and the brush things are a waste of time.
I've heard of many reports of them being struck. Sometimes spraying hot
metal around and causing a fire hazard. And you still should have a good
ground even with those. To me, the only sure thing is expecting the
strike to happen, and safely controlling it's path to ground when it
finally does. So I'm firmly with polyphaser on that one. MK
--
http://web.wt.net/~nm5k

There is a short video available (saw in a search of lightning arrestor
systems) that shows the Empire State Bldg being struck several times, and
not once does the lightning "visibly" hit, follow, or otherwise act
impressed with the elaborate grounding system on the building. Taken as a
whole though, it must be effective, because the strikes do no apparent
damage, and they obviously get to the ground somehow.

JP

"Mark Keith" wrote
The last class I had at work on electrical safety was pro
lightening rods AND ground systems. (as was the one for skywarn from
the NWS)

I agree there, if he is talking about the traditional pointy lightning
rod used to protect other gear or buildings. I'm of the opinion strikes
can never be totally avoided, and the brush things are a waste of time.
I've heard of many reports of them being struck. Sometimes spraying hot
metal around and causing a fire hazard. And you still should have a good
ground even with those. To me, the only sure thing is expecting the
strike to happen, and safely controlling it's path to ground when it
finally does. So I'm firmly with polyphaser on that one. MK