On Jul 13, 12:52*am, Richard Clark wrote:
On Mon, 12 Jul 2010 21:21:24 -0700 (PDT), Tom Horne

wrote:
Can anyone make a recommendation, based on actual training and
experience, as to what width and thickness of copper strap would be
needed as the down conductor from the antenna mounts at the peak of my
house roof, some twenty five feet above local terrain.

Hi Tom,

Consult the NEC code for your area. *I have never seen them specify
strap in any situation, and don't try your own interpretations of what
"continuous"or "direct" means.

73's
Richard Clark, KB7QHC

Richard
I will certainly make the installation code compliant. What I was
looking for help on was how to make it effective in avoiding damage
from lightning. I have read all of the applicable material from the
Polyphaser, NIST, and several other sites but what I was hoping to
elicit was specific guidance on what size strap to use for the down
conductors and what size to use for the ground ring so that they might
actually work rather than just comply with the code. I can certainly
add any regular wire conductor that would keep the electrical
inspectors happy since I already have 2/0 bare copper for the ground
ring; were only #2 is required and, the ridiculously undersized,
number ten that the code requires for down conductors in hand.

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.

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.
If metal enclosures such as steel conduit are used to enclose the
grounding conductor, bonding must be provided at both ends to ensure
an adequate low-impedance current path.
(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.
(F) Electrode. The grounding conductor shall be connected as
follows:
(1) To the nearest accessible location on the following:
a. The building or structure grounding electrode system as covered in
250.50
b. The grounded interior metal water piping systems, within 1.52 m (5
ft) from its point of entrance to the building, as covered in 250.52
See the commentary following 250.52(A)(1).
c. The power service accessible means external to the building, as
covered in 250.94
d. The metallic power service raceway
e. The service equipment enclosure, or
f. The grounding electrode conductor or the grounding electrode
conductor metal enclosures; or
(2) If the building or structure served has no grounding means, as
described in 810.21(F)(1), to any one of the individual electrodes
described in 250.52; or
(3) If the building or structure served has no grounding means, as
described in 810.21(F)(1) or (F)(2), to an effectively grounded metal
structure or to any of the individual electrodes described in 250.52.
(G) Inside or Outside Building. The grounding conductor shall be
permitted to be run either inside or outside the building.
(H) Size. The grounding conductor shall not be smaller than 10 AWG
copper, 8 AWG aluminum, or 17 AWG copper-clad steel or bronze.
(I) Common Ground. A single grounding conductor shall be permitted for
both protective and operating purposes.
(J) Bonding of Electrodes. A bonding jumper not smaller than 6 AWG
copper or equivalent shall be connected between the radio and
television equipment grounding electrode and the power grounding
electrode system at the building or structure served where separate
electrodes are used.

--
Tom Horne, W3TDH

On Thu, 15 Jul 2010 18:32:02 -0700 (PDT), Tom Horne
wrote:

Richard
I will certainly make the installation code compliant. What I was
looking for help on was how to make it effective in avoiding damage
from lightning.

Hi Tom,

Then that is the end of it. ...but I see more writing below....

I have read all of the applicable material from the
Polyphaser, NIST, and several other sites but what I was hoping to
elicit was specific guidance on what size strap to use for the down
conductors and what size to use for the ground ring so that they might
actually work rather than just comply with the code.

This borders on regret - for what, I haven't a clue.

I can certainly
add any regular wire conductor that would keep the electrical
inspectors happy since I already have 2/0 bare copper for the ground
ring; were only #2 is required and, the ridiculously undersized,
number ten that the code requires for down conductors in hand.

This is not a beauty contest for the diversion of inspectors.

Forgive my not continuing to quote you further as I see that it
NOWHERE employs strap in its description of conductors.

Here is a clue. Call up your insurance agent that provides coverage
for your house against lightning strike. Ask him if your policy would
be honored if your home did not conform to code. Ask him how many
claims had been made for lightning damage to homes that did conform to
code.

73's
Richard Clark, KB7QHC

Tom Horne wrote:
On Jul 13, 12:52 am, Richard Clark wrote:
On Mon, 12 Jul 2010 21:21:24 -0700 (PDT), Tom Horne

wrote:
Can anyone make a recommendation, based on actual training and
experience, as to what width and thickness of copper strap would be
needed as the down conductor from the antenna mounts at the peak of my
house roof, some twenty five feet above local terrain.
Hi Tom,

Consult the NEC code for your area. I have never seen them specify
strap in any situation, and don't try your own interpretations of what
"continuous"or "direct" means.

73's
Richard Clark, KB7QHC

Richard
I will certainly make the installation code compliant. What I was
looking for help on was how to make it effective in avoiding damage
from lightning. I have read all of the applicable material from the
Polyphaser, NIST, and several other sites but what I was hoping to
elicit was specific guidance on what size strap to use for the down
conductors and what size to use for the ground ring so that they might
actually work rather than just comply with the code. I can certainly
add any regular wire conductor that would keep the electrical
inspectors happy since I already have 2/0 bare copper for the ground
ring; were only #2 is required and, the ridiculously undersized,
number ten that the code requires for down conductors in hand.


Hmmm you say "ridicuously undersized"..

Why?

have you studied the fusing current of AWG 10?
Have you compared the inductance of various sizes?

Do you know *why* the code only requires AWG 10?

The code requirements are based on actual science, engineering, and test
data, so if the code requires AWG 10, it's probably for a fairly good
reason.

Note that they allow bronze and copper clad steel as well as solid
copper, so clearly, DC resistance isn't what they're worried about.

(hint.. think of mechanical reasons)

Note, especially, that the NEC (NFPA 70) grounding/bonding requirements
are NOT for lightning protection. (that's in NFPA 780, not NFPA 70)

On 7/19/2010 10:54 AM, Jim Lux wrote:
Tom Horne wrote:
On Jul 13, 12:52 am, Richard Clark wrote:
On Mon, 12 Jul 2010 21:21:24 -0700 (PDT), Tom Horne

wrote:
Can anyone make a recommendation, based on actual training and
experience, as to what width and thickness of copper strap would be
needed as the down conductor from the antenna mounts at the peak of my
house roof, some twenty five feet above local terrain.
Hi Tom,

Consult the NEC code for your area. I have never seen them specify
strap in any situation, and don't try your own interpretations of what
"continuous"or "direct" means.

73's
Richard Clark, KB7QHC

Richard
I will certainly make the installation code compliant. What I was
looking for help on was how to make it effective in avoiding damage
from lightning. I have read all of the applicable material from the
Polyphaser, NIST, and several other sites but what I was hoping to
elicit was specific guidance on what size strap to use for the down
conductors and what size to use for the ground ring so that they might
actually work rather than just comply with the code. I can certainly
add any regular wire conductor that would keep the electrical
inspectors happy since I already have 2/0 bare copper for the ground
ring; were only #2 is required and, the ridiculously undersized,
number ten that the code requires for down conductors in hand.


Hmmm you say "ridicuously undersized"..

Why?

have you studied the fusing current of AWG 10?
Have you compared the inductance of various sizes?

Do you know *why* the code only requires AWG 10?

The code requirements are based on actual science, engineering, and test
data, so if the code requires AWG 10, it's probably for a fairly good
reason.

Note that they allow bronze and copper clad steel as well as solid
copper, so clearly, DC resistance isn't what they're worried about.

(hint.. think of mechanical reasons)

Note, especially, that the NEC (NFPA 70) grounding/bonding requirements
are NOT for lightning protection. (that's in NFPA 780, not NFPA 70)


IIRC the purpose is to primarily drain off the static charges so the
gnd-cloud potential difference is minimized. A direct strike will
usually just melt whole house wiring, etc. etc.

Marv

IIRC the purpose is to primarily drain off the static charges so the
gnd-cloud potential difference is minimized. A direct strike will
usually just melt whole house wiring, etc. etc.

Not true.

The cloud has SO MUCH charge you don't stand a chance of bleeding it off.

Direct strikes are typically around 20 kA, and can be as high as 100kA.
Both can be adequately carried by the usual AWG6 wire, because the
current pulse only lasts a few microseconds.

"Jim Lux" wrote
...


IIRC the purpose is to primarily drain off the static charges so the
gnd-cloud potential difference is minimized. A direct strike will usually
just melt whole house wiring, etc. etc.

Not true.

The cloud has SO MUCH charge you don't stand a chance of bleeding it off.

Each cloud has a charge and the all is flowing to the ground. But only 20%
as the direct stroke.

The rule is simple. A mast with the polished ball on the tip attract the
direct stroke (polished ball do not dissipate).
A mast with many sharp spikes dissipate the static charge and eliminate the
direct strike.

Direct strikes are typically around 20 kA, and can be as high as 100kA.
Both can be adequately carried by the usual AWG6 wire, because the current
pulse only lasts a few microseconds.

It is the oscillating current which has a canal in the air. It is not
obliged to flow only in the wire.
S*

On Jul 23, 8:48*am, "Szczepan Bialek" wrote:
*"Jim Lux" ...



IIRC the purpose is to primarily drain off the static charges so the
gnd-cloud potential difference is minimized. A direct strike will usually
just melt whole house wiring, etc. etc.

Not true.

The cloud has SO MUCH charge you don't stand a chance of bleeding it off.

Each cloud has a charge and the all is flowing to the ground. But only 20%
as the direct stroke.

The rule is simple. A mast with the polished ball on the tip attract the
direct stroke (polished ball do not dissipate).
A mast with many sharp spikes dissipate the static charge and eliminate the
direct strike.

wrong, sharp spikes are designed to start an upward streamer that
connects the downward leader to the lightning rod. that is why they
have a sharp point, to reach the breakdown field gradient before
anything else around them.



Direct strikes are typically around 20 kA, and can be as high as 100kA.
Both can be adequately carried by the usual AWG6 wire, because the current
pulse only lasts a few microseconds.

It is the oscillating current which has a canal in the air. It is not
obliged to flow only in the wire.
S*

normally they don't oscillate, it is a mono-polarity pulse.

"K1TTT" wrote
...
On Jul 23, 8:48 am, "Szczepan Bialek" wrote:
"Jim Lux"
...



IIRC the purpose is to primarily drain off the static charges so the
gnd-cloud potential difference is minimized. A direct strike will
usually
just melt whole house wiring, etc. etc.

Not true.

The cloud has SO MUCH charge you don't stand a chance of bleeding it
off.

Each cloud has a charge and the all is flowing to the ground. But only
20%
as the direct stroke.

The rule is simple. A mast with the polished ball on the tip attract the
direct stroke (polished ball do not dissipate).
A mast with many sharp spikes dissipate the static charge and eliminate
the
direct strike.

wrong, sharp spikes are designed to start an upward streamer that
connects the downward leader to the lightning rod. that is why they
have a sharp point, to reach the breakdown field gradient before
anything else around them.

But before the steamer is the dissipating: " IIRC the purpose is to
primarily drain off the static charges so the
gnd-cloud potential difference is minimized"

Direct strikes are typically around 20 kA, and can be as high as 100kA.
Both can be adequately carried by the usual AWG6 wire, because the
current
pulse only lasts a few microseconds.

It is the oscillating current which has a canal in the air. It is not
obliged to flow only in the wire.
S*

normally they don't oscillate, it is a mono-polarity pulse.

Normally in ALL sparks current oscillates: " The storm detector is a radio
receiver .
"The device was invented in 1894 by Alexander Stepanovich Popov. It also was
the first radio receiver in the world.
Ground-based and mobile detectors calculate the direction and severity of
lightning from the current location using radio direction-finding techniques
together with an analysis of the characteristic frequencies emitted by
lightning"

S*

On Jul 23, 3:48*am, "Szczepan Bialek" wrote:


The rule is simple. A mast with the polished ball on the tip attract the
direct stroke (polished ball do not dissipate).
A mast with many sharp spikes dissipate the static charge and eliminate the
direct strike.

A mast with a ball is less likely to attract a strike. That is why
they are
used on flag poles, etc.. They don't stream near as well as a sharp
point. They can still be struck though if nothing more attractive
is around as far as streamers.
A pointed mast streams much easier and will be much more
effective as a lightning rod.
A mast with a lot of spikes is wishful thinking. You can not bleed
off the charge fast enough to eliminate strikes. It's like whizzing
in a whirlwind.
You can not eliminate a direct strike by bleeding off the charge.
You can only offer it a better and easier streaming target than
whatever you do not want struck. And the sharper and more
pointy an object, the better it streams. When is the last time
you saw a lightning rod with a polished ball on top?
They don't sell them, as they would be fairly useless.

wrote:
On Jul 23, 3:48 am, "Szczepan Bialek" wrote:

You can not eliminate a direct strike by bleeding off the charge.
You can only offer it a better and easier streaming target than
whatever you do not want struck. And the sharper and more
pointy an object, the better it streams. When is the last time
you saw a lightning rod with a polished ball on top?

Actually, air terminals with blunt ends and sphere ends have been tested
by Erico, and they work about the same as the traditional "Franklin"
style with the pointy end.

They don't sell them, as they would be fairly useless.

That's not because they work or don't work, it's because fashion
dictates pointy end. You'd have to have a substantial performance
improvement to justify something different (i.e. to be unfashionable, it
had better give you something else).


At the fields in play here, whether you have a 1/10" radius or a 1/2"
radius or 3" radius, it doesn't make much difference.

the breakdown voltage for a curved surface is roughly 3MV/meter or
70kV/inch.

So a 1/2" diameter rod (1/4" radius at largest) will breakdown at about
17-18 kV. A 6" diameter ball breaks down at 200kV or so (assuming it's
perfectly smooth, etc.)

The "free air" electric field without a storm around is on the order of
100 V/meter, rising to 10-20 kv/m under a storm. So, get 10-15 meters
up, and you've got your 200kV needed to start corona on even a pretty
big diameter thing.

If the ball is wet, especially with distinct droplets, then you can get
corona forming much earlier. The electrostatic forces tend to make the
droplets fly off.