[TowerTalk] Grounding of cables to tower? (N3AE)

[jimlux]

On 10/19/17 1:46 PM, Jim Brown wrote:
> On 10/19/2017 12:26 PM, jimlux wrote:
>> Interesting.. I'll have to go look up the history of that change. 
>> There must have been some problem.
> 
> NEC has ALWAYS prohibited more than one neutral to ground bond in a 
> system, and has always required earth electrodes for every building. As 
> you noted earlier, the addition of a transformer establishes a new 
> system, where there must be a neutral to ground bond. I have great 
> respect for those who produced and update NEC (although the section on 
> Antennas is pretty dated, and seems focused solely on the possibility of 
> wires falling on power lines).

Dated is the word  - I think it was last revised when people were using 
toploaded "aerials" with copper clad steel.

But yes, if there was a change to require ground bonding between 
buildings, it must have been for some good reason.  Perhaps the 
increasing use of coax, which then became the "de facto" bonding 
conductor, which is generically a *bad thing*.

At some point, though, the ground bonding requirement goes away - 
there's no bonding conductor between successive transformers on 
residential service along a street. The individual houses are "sort of" 
bonded because the neutral conductor is connected to earth ground at 
each house, and all connected together at the distribution transformer 
on the pole.  (and, of course, "broken neutral" causes all kinds of 
interesting phenomena - when you turn your lights on and off, the 
voltages on your neighbor's two phases change)



> 
> As a member of the Standards Committee of the Audio Engineering Society, 
> I've been part of many hundreds of discussions on the fine details and 
> possible repercussions of almost every word in a Standard. Like the 
> engineers who produce NEC, the AESSC includes membership from a very 
> broad range of disciplines, and the resulting perspectives yields many 
> "what if" scenarios. Likewise, as the sound system consultant to 
> architects designing buildings, more "what if" scenarios. 

That's why I'm interested in why it changed - I'm sure it's an 
interesting scenario.


Things might
> have been very different if only such collaborative design and the right 
> "what if" questions had been raised during the design meetings that put 
> the generators at the Fukushima nuclear power plants in the basement.
> 
> Chicago learned this lesson 20 years ago when basement generators 
> flooded after an accident on the Chicago River caused it to back up into 
> downtown buildings. Cities in New York, New Jersey, Florida, and Texas 
> have all learned it after major hurricanes.

sort of - they moved the generators up, but not the fuel tanks, or vice 
versa.. The code evolves, though.
> 
> Bottom line is that good engineers (as well as business and political 
> leaders) keep open minds and learn from history, and from each other.
> 

Indeed they do.



> 73, Jim K9YC
> 
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