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