[TowerTalk] Does prevailing grounding scheme promote large ground loop

[Steve London]

K9YC wrote:

>The problem with this (and any) analysis of a lightning event is that it is FAR more >complicated than anything we can compute, simply because the voltages and currents induced >in any system (stuff wired together) will be different in each conductor depending on >WHERE the strike is, the physical geometry of the conductors that make up that system, how >energy from the strike gets to the earth, etc.

I can attest to that ! In 13 years of living on a dry, New Mexico 
hilltop, I have learned a lot about mitigating lightning damage. 
Frankly, the cost and effort of doing lightning protection "perfectly 
right" is prohibitive. The approach I have settled on is simple 
disconnection to keep the bulk of the lightning energy out of the house. 
All RF and control cables to/from the towers (I have 3 towers, with 5 
rotator controls and a number of remote antenna switches) terminate on a 
bulkhead panel about 30 feet from the house. During lightning season 
(May-October), everything is disconnected at the panel, except when I am 
on-the-air. All AC power to the ham shack is disconnected, except when I 
am on-the-air (unplugged - I don't trust the small air gap in switches 
and relays). Yes, this makes it inconvenient to be on-the-air during the 
summer. Even with these measures, I have learned the hard way about 
interconnectedness (K9YC's "stuff wired together"). A nearby or direct 
hit to a tower will destroy USB ports on computers and radios, if they 
are interconnected with a USB cable. I have tried commercial USB 
optoisolators, but have found they generate too much RF noise. The 
latest incident was earlier this week. I had a direct hit. The only 
"stuff wired together" was an Astron power supply, connected to a 2 
meter radio. Just before the storm, these were working fine. I unplugged 
the antenna from the 2 meter radio, and the AC power from the power 
supply. There was still a 3' long power cable connecting the power 
supply and 2 meter radio. After the storm, the power supply blew fuses. 
The root cause was a fried LM723 in the power supply, causing the 
voltage to go high, and the crowbar protection to be activated.

Sometimes I think moving to relatively lightning-free coastal Oregon 
would be a good idea !

73,
Steve, N2IC