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#25342 - 05/05/03 10:09 PM Earth voltage  
ga.sparky56  Offline
Member
Joined: Nov 2002
Posts: 558
young harris georgia usa
The question: If I drive 2 ground rods,say 100' apart and put a meter lead on each one,will I get a voltage reading? Why or why not? Then you can thrash me for not knowing!


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#25343 - 05/05/03 11:12 PM Re: Earth voltage  
Bjarney  Offline
Moderator
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
Two guesses… If the rods are of different metals, the two combined with soil moisture could form an electrochemical cell [battery] giving a low DC voltage. If there is a utility-distribution multigrounded neutral in the area, it may be possible to read some 60Hz voltage, like measuring taps on an energized resistor.


#25344 - 05/06/03 12:06 AM Re: Earth voltage  
George Corron  Offline
Member
Joined: May 2001
Posts: 717
Lorton, Va USA
If you use a galvanometer, you would have some luck. The concept of earth as a large electric sponge is a myth, especially now days with the utility neutral mentioned above, RF, etc..

Galvanometers can be made easily, hard to calibrate a home made though. I have one on my earth resistance meter, and it never fails to surprise me what comes from the ground...... OK, maybe the term is scares me.

I guess the answer is with a real sensitive meter, probably. BTW, rural is no protection, the worst I ever saw was in a VERY rural (I'll tell ya how rural, even Sparky66wv would think he was in the woods [Linked Image] )location with an earth return neutral..... dang near ruined my meter.


#25345 - 05/06/03 01:23 AM Re: Earth voltage  
Bjarney  Offline
Moderator
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
About a year ago there was a thread about "S.W.E.R."
http://electrical-contractor.net/ubb/Forum1/HTML/001230.html

This would probably give driven rods a little higher readings.


#25346 - 05/06/03 08:16 AM Re: Earth voltage  
wocolt  Offline
Member
Joined: Dec 2002
Posts: 110
I would think it would be very possible to read voltage between the two rods, aganin as mentioned depending where you are.
Part of the problem is the utility's grounding the primary neutral to the secondary neutral as the loads increase on the secondary side of the transformer the neutral current from the primary will increase to carry the load. It will apear on the secondary side because of the grounding.
For some reason farms have a much bigger problem with this than cities do.
Another thing is our system of grounding we go to the water pipe and Now drive two ground rods. At this point depending on the relative size of resistance the neutral return current will take these alternate pathes back to the transformer/source, creating Objectionable current on our system. I am not sure when they started grounding the systems but as it is we are standing on 1/2 of the circuit that is the neutral.
I am not saying it is a bad system but like anything else it has its flukes and this is one of them.

WmnColt



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