On Monday 12 April 2004 04:39 am, Richard Urwin wrote: > On Monday 12 Apr 2004 11:21 am, Aron Smith wrote: > > On Monday 12 April 2004 01:47 am, John Wilson wrote: > > > On April 11, 2004 07:39 pm, Marc wrote: > > > . > > > > > > In the vast majority of cases two grounds will simply, as you say, > > > make things worse. > > > > Can't see that electricity is going to follow Ohms law and go the > > path of least resistance so 2 grounds would be (r1+r2)/(r1*r2) =Rt > > There are two things wrong with this. > Firstly, ground is not a perfect conductor. Many cows die because their > feet are different distances from a lightning strike, creating a > voltage of several thousand volts across the length of the cow. There > will be a similar voltage between your two earth rods. A potential difference is one thing but as you know This is mostly skin effects. the key is proper grounding and having 2 grounds is preferable to having 1 ground that makes sharp turns eg 90 deg Lighting strikes start at the ground and travel up. thats why a lighting rod has a pointy tip to bleed off the potential. > > Secondly, lightning is high frequency and unimaginably high voltage. It > behaves in strange ways that are still imperfectly understood. > > In addition it may create an earth loop, which is basically an antenna. > (My HiFi used to pick up Radio Moscow until I removed one of the > earths.) Your earth wiring could pick up an induced voltage from a > nearby lightning strike and fry equipment that would otherwise be safe. You had a n imperfect ground also known as a rectifying ground thats basic radio theory For a good coverage of this subject I recommend "The ARRL Radio Amateur's Handbook"
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