[time-nuts] Lightning arrestors for GPSDO antenna
wb4gcs at wb4gcs.org
Fri Oct 17 12:51:30 EDT 2014
Some very good information here.
I use NFPA codes in my day job.
JUST YESTERDAY, I learned that you can read their standards for free.
Go to their site, and you'll see a link for free access to any of their
standards. You can't save or print, but you can read. You will have to
create an account, but they don't demand anything that isn't already public.
wb4gcs at amsat.org
On 10/17/2014 12:11 PM, Jim Lux wrote:
> On 10/17/14, 8:17 AM, Chris Albertson wrote:
>>> You can use metal conduit as the bonding conductor between grounding
>>> systems, for one thing.
>> That works fine, but I think it is disallowed by the electrical
>> code. If
>> you used metallic conduit it MUST be grounded but you can't use it for
>> grounding. That said, it does work. I think the danger the
>> electric code
>> addresses is that connections between conduit sections become loose over
>> time and might corrode.
> The metallic raceway (code speak for conduit) is allowed to be the
> bonding conductor (bonding conductor = "greenwire" or "electrical
> safety" ground in code speak). Properly installed conduit will have a
> good connection, etc..
> When interconnecting multiple grounding electrodes or electrode
> systems is where the requirements for particular gauges of wire come
> in, and mostly it has to do with mechanical strength and reliability.
> You can use a smaller conductor if it is protected inside something,
> for instance. The other rule is that the bonding conductor has to be
> continuous (the concern you mentioned about connections becoming
> loose, etc).
> is a very nice summary
> Mike Holt (http://www.mikeholt.com/) has a great website on all code
> related issues, and he's written a bunch of articles that explain the
> code and the rationale behind the requirements.
> And when it comes to antennas and the like, you're in a different
> section of the code 810, 820, and the requirements for the grounding
> conductor (and whether coax shield can be that grounding conductor)
> are all laid out there.
> In many case, the coax shield can serve as the grounding conductor,
> but only if there are no connectors in the path (i.e. you have to have
> a clamp that directly contacts the shield where it interconnects with
> the building grounding system). A barrel feedthrough in a grounded
> metal panel doesn't meet the strict requirements of the code (although
> personally, I think it's a fine solution)
> One thing to remember about the NEC requirements is that the "threat"
> they are protecting against with the grounding and bonding
> requirements is NOT a lightning strike. It's contact with an
> energized conductor (e.g. a power line touches your antenna or
> supporting structure). That's a whole lot more common (wind storms,
> etc.) NFPA 780 is the lightning protection code, and has a lot more
> "lightning protection" aspects.
> The NEC cares almost nothing about transient protection, the concern
> is more about electrical shocks and burning the building down.
> Furthermore, the NEC really only regulates the wiring in your
> building, and nothing that is connected to it, nor does it regulate
> the wiring of the power company.
> There are two tomes of reference I use for transient protection: one
> is IEEE 1100 (the Emerald Book) which has gone under many names over
> the years (politics.. computer manufacturers did not want their
> equipment described as "sensitive electronic equipment")
> The other is "Protection of Electronic Circuits from Overvoltages" by
> R.B. Standler.
> And, if you're at the Dover Pubs store.. take a look at the books
> about lightning from Martin Uman. Very readable, lots of technical info.
>> I think the threaded conduit would work fine. That stuff is like water
>> pipe but smoother inside.
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