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Old 09-06-2008, 10:02 AM   #16
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Hypothetical Lightning/Grounding question


You personally attacked me in post #8, #10 and #13. I was only responding. I apologize for any offense. I know you are a very competent electrician by your many posts and it would be a shame to lose you. Sorry again!

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Old 09-06-2008, 10:50 AM   #17
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Hypothetical Lightning/Grounding question


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You personally attacked me in post #8, #10 and #13. I was only responding. I apologize for any offense. I know you are a very competent electrician by your many posts and it would be a shame to lose you. Sorry again!
I apologize also. I didn't see my posts as attacking you but in re-reading them I can see the problem. Sorry about that. A truce is in order.
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Old 09-06-2008, 02:13 PM   #18
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Hypothetical Lightning/Grounding question


While there are an infinite number of paths, and infinite number of them are infinitely long... The way you describe it, ground resistance should be zero, but its not. Stab two probes of your ohm meter into the dirt, should be able to measure resistance. In fact, once I find my ohm meter, I am going to do just that.
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Old 09-06-2008, 04:34 PM   #19
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Hypothetical Lightning/Grounding question


In the sand we live in we cannot get a low enough resistance for a single ground rod so we are required to use two for electrical services.

We also have a real problem with stray voltage on farms.

When you do your test, try it in dry ground and then add some water.
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Old 09-06-2008, 06:31 PM   #20
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Hypothetical Lightning/Grounding question


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When you do your test, try it in dry ground and then add some water.
I hate to always be the dissenting voice, but water is actually an insulator

Pure water that is.

Just trying to lighten up the mood a little bit, but it's true!
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Old 09-07-2008, 09:33 AM   #21
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Hypothetical Lightning/Grounding question


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I hate to always be the dissenting voice, but water is actually an insulator

Pure water that is.

Just trying to lighten up the mood a little bit, but it's true!
You're right. But mix in some dirt and the water makes the dirt a good conductor.

That reminds me of an OSHA course I took some years back. One of the things we learned was voltage gradients. As the only Electrician in a class full of OSHA inspectors I got to be the guinea pig.

The instructor filled a glass cake pan full of distilled water. He took out a two wire cord with a small plate connected to the end of each conductor. He dropped one plate into the water on each end of the pan. Then he plugged the cord into a 120v floor receptacle. Carpeted floor by the way.

He brought me up and had me put two fingers in a V and dip them into the pan cross ways to the plates. Then with my fingers in the water he had me rotate my fingers slowly to be in line with the plates. Nothing happened.

He then stirred in a handful of salt. I again put my fingers in the pan the same way. I felt nothing with my fingers cross ways to the plates. But this time when I rotated my fingers I felt current flowing up one finger and down the other. I could only get about 45 degrees before it started to hurt enough to stop.

We then spent the rest of the morning on gradients, getting cranes and cars into high voltage power lines, lightning strikes, etc.

It was a cool demonstration. The movie he showed of actual arcing and sparking cases was pretty awesome too.
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Old 09-08-2008, 11:00 AM   #22
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Hypothetical Lightning/Grounding question


Yeah, salt does wonders to increase the conductivity of water. In railroad signaling, grade crossings through urban areas can be a real problem in the winter. Road salt combined with snow/slush tends the greatly increase the inter-rail current leakage at the crossings causing false activation of the warning devices/gates.

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