[TowerTalk] art and science of lightning protection book

[jimlux]

Kevin Normoyle wrote:
> The 2004 version of NFPA 780 is available here as pdf What do people 
> think of that?
> 
> http://www.atmo.arizona.edu/students/courselinks/spring07/atmo589/articles/NFPA_780_2004.pdf
> 
> 
> The problem is: does anyone really do all the recommendations?
> re K9YC's comment, they concur:
> 
> page 35
> 
> 4.14 Common Grounding.
> 4.14.1 General. All grounding media in or on a structure shall be interconnected
> to provide a common ground potential.
> 4.14.1.1 This interconnection shall include lightning protection, electric
> service, telephone, and antenna system grounds, as well as underground metallic piping systems.
> 
> 
> They mention radio antennas.
> Curiously, as a side note about the reference to using a coil to impede lightning...they mention bypassing coils because of their impedance:
> 
> page 58
> 
> "8.3.5.3 Because a loading coil presents a high impedance to the flow of lightning currents, the coil
> shall be shorted, equipped with a surge suppression device (lightning arrester) for bypassing the
> lightning current, or grounded above the coil."
> 
> 
> I guess you could argue, it either does, or it doesn't.
> 


This presumably refers to things like broadcast antennas (or Omega 
stations), which have a loading coil at the base, and yes, putting a 
spark gap across the coil would be a "good" idea.  The "grounded above 
the coil" might be a for a system where the coil is in series with the 
transmission line.