[time-nuts] GPS antenna and lightning and power

phil fortime at bellsouth.net
Mon Oct 5 07:21:13 UTC 2009


----- Original Message ----- 
From: "Bill Hawkins" <bill at iaxs.net>
To: "'Discussion of precise time and frequency measurement'" 
<time-nuts at febo.com>
Sent: Monday, October 05, 2009 3:11 AM
Subject: Re: [time-nuts] GPS antenna and lightning and power


> Group,
>
> I understand the need for an equipotential plate at the building
> entrance, with a good ground connection. I also understand the need
> for a single point ground and, if possible, a metal ground plane
> under the equipment that is also returned to a single point.
>
> So far, this has been applied to the cables from antennas.
>
> What about the power company ground? These wires also enter the
> equipment, but they are not connected to the common ground. Even
> if they were, the pole transformer wouldn't handle the voltage
> rise from the usual poor earth ground at the equipotential plate.
>
> A nearby strike can cause a high electric field in the dirt. One
> example is the well pipe. Another is dead cows standing with
> their feet apart (as they must). Or dead golfers.
>
> The EMP problem is not affected by grounding at all. In fact, a
> good ground at the building just strengthens the EMP and puts it
> closer to the building.
>
> At least, that's how I understand it.
>
> Bill Hawkins


Mountaintops are unique in some respects, with Kevins terminology I would 
guess he is in the electrical business. Grounds for RF, Lightning, and 
electrical have little in common other than name. What is a good electrical 
ground may conflict with a good lightning or RF ground.

A mountain I am thinking of is primarily rock where holes were blasted in 
solid rock for the tower legs. For grounding, tons of copper sheets/plate 
was buried below what dirt is in the area. At considerable expense, they did 
manage to get about 25 Ohms above ground. When a dark cloud is on the 
horizon, the power lines are switched off and they go on Cat diesel 
generators and stay on them as long as the threat of a storm exists. Should 
they take a hit and fail to switch off the power companies lines, it will 
drop the power lines coming up the mountain.

The building is steel reinforced concrete and in essence a faraday cage. 
Tower, building, and contents are all the same potential, like the bird on 
the power line. No damage results BUT it can be one hell of a show with St. 
Elmo's fire and ball lightning. It's harmless, but a newcomer to the 
building in a storm may be found on top of the card table in the fetal 
position with the ball lightning rolling around. The lightning charge itself 
may travel a little further along the ground before it dissipates, but as 
long as you are in the building (faraday cage) and not standing in the area 
outside, you and all the equipment are ok.

Here is a super interesting short video of men inspecting "live" hi-voltage 
power lines.
Just like that bird on the wire. http://www.youtube.com/watch?v=9tzga6qAaBA

Phil




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