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. I have a a
mount for an antenna at one gable end and a mount for a weather
station sensor array at the other. What thickness and width should I
use in the earth between the two Grounding Electrode Systems. I will
drive five eighths inch copper rods, each eight feet long as far out
from the foundation as I can get them or eight feet were possible. On
one end that will be only six feet due to the proximity of the
property line. At all of the other rod locations I will be able to
keep them at least eight feet from any underground obstructions. To
compensate for the proximity to the foundation wall to the first rod
I will use rod couplers and drive it to hard rock or sixteen feet
whichever comes first. I'm guessing that in keeping the remaining
rods at least eight feet out from the foundation and sixteen feet
apart that I will only have four rods total in a ring around the back
side of the house. What is the best way to attach the copper strap to
the support masts and eve brackets themselves? Do you know of
anything that will make a good connection to the one inch galvanized
iron pipes that I'm using for support masts?

Can you recommend a technique for bonding the interior grounding buss
at the operating position to the exterior vertical copper strap. I
have no idea how that is usually done.
--
Tom Horne, W3TDH

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

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.

Tom Horne wrote in news:e802f6fa-b0e1-471b-bf31-
:

Can anyone make a recommendation, based on actual training and
experience, as to what width and thickness of copper strap would be ...

In this part of the world, we have an Australian / New Zealand Standard
(our version if you like of ANSI, BS etc) which explains the rationale
behind lightning protection, a method of estimating the downcurrent for
protection design purposes and a process for designing down conductors.

Broadly, the scheme is that downconductors are designed to withstand a
few donwstrokes in quick succession without melting the down conductor.
If you work from a peak current of 20kA, it would lead to a down
conductor in copper of at least 25mm^2 which is about #2 to you folk.

I regularly see hams recommend much thinner down conductors, and can only
assume that there is not regulatory guidance or requirement, and I wonder
at the effectiveness of using #6 as often recommended, especially
aluminium as is often the case. Note that reducing conductor size is a
double whammy, you increase the resistance (so the power), and decrease
the mass that has to be heated to melting point, and so the energy
required.

But, firstly, you should determine if there are regulatory requirements,
such as NEC etc.

The question of equipotential bonding conductors ought be dealt with in
the same way, though that is not to imply that they will be the same
size.

Owen

Owen Duffy wrote in
:

....
But, firstly, you should determine if there are regulatory
requirements, such as NEC etc.

Is "NFPA 780: Standard for the Installation of Lightning Protection
Systems" a relevant standard in your jurisdiction?

Owen

Owen Duffy wrote in news:Xns9DB5277B6263Bnonenowhere@
61.9.134.55:

....
Is "NFPA 780: Standard for the Installation of Lightning Protection
Systems" a relevant standard in your jurisdiction?

If it is applicable, it seems that for a Class 1 structure (less than 75'
in height???), the requirement for the main down conductor is 57,400
circular mils CSA if copper, that is about 29mm^2 or #2 conductor.

By contrast, #6 is 26,000 circular mils, has approximately twice the
resistance per unit length, half the mass per unit length, and somewhere
just less than 25% of the stroke current withstand of #2.

Owen