# Ground potential differnet between 2 bldgs

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Why would there be a 3 volt difference between the grounds on 2 buildings that are wired to the same meter?

I have an out building at my house which is wired to the hosue but the ground reads voltage between the house and the out building's wiring..

Is this usual?

thanks

- Mike

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Yes, If you want them at the same potential then you are going to have to run a seperate ground wire from your out building to your main buildings ground connection point. Depending on the distance will deturmine the ground wires gauge. You can try adding a new ground rod to your out building and your main building. A Hammer drill works great for driving in ground rods. Re do and retighten all of your grounds.

RJ

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Mike-

The 3 volts is probably caused by different currents flowing in the two

240 VAC lines.

The difference current flows through the neutral wire back to the transformer on the power pole, and a voltage difference will exist due to the IR-drop. In other words, you are only measuring part of the circuit. There is likely more voltage dropped between the transformer and the main power box at the house.

Another interesting measurement is the difference between each side of the

240 VAC and neutral. I had a problem with bright flickering lights and found there was a loose connection where the neutral wire connected inside the main power box. If the connection had completely broken, there might have been equipment damage resulting from unbalanced loads causing wildly different voltages on the two sides.

Three volts sounds low, but it could be the symptom of a more serious problem.

Fred

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Another interesting measurement is the difference between each side of the

I was thinking that the neutral / ground wire might have a bad connection and was actually worrying about exactly what you were saying.. I guess I'll check out the neutral lug in the main breaker panel.

-Mike

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Yes, there will usually be a potential difference between different ground points remote from each other, even if they are electrically bonded. It depends largely on the earth resistivity at the remote point and the wire gauge used for the run back to the main distribution ground point.

Essentially, to provide a good grounding system at a location you need to have multiple ground rods (each one at least 3M long) driven into the ground at selected locations determined by resistivity testing, and then interconnectiong all of them using an appropriate gauge conductor and then bonding this network to the main earth point for the property. Can be a very expensive project.

In telecommunications, every major telephone exchange will have an extensive matting of heavy gauge copper mesh buried deep below the building and extending for some distance around the perimeter in order for the lowest possible earth resistance to be obtained. When checking the potential difference between the exchange earth and the earth provided for the electrical supply, it is not unusual for a heavy current of many amps to be measured, thus indicating a substantial difference in resistance between the 2 earths.

Here's an Australian website blurb on ground rods and their use.

Galmar is a Polish company so visit their website.

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Yes, earth has its own conductivity and voltage differences.... I read an idea just stringing a long wire east/west would generate electricity...never tried it... I know they tried it in space once...

But in La Canada, CA, my uncle built our home on a mountain in DG (decomposed granite) and because of such long run of pipes, he made a really good ground...said its from old days of farm houses that had lightning rods on the barns....

He dug a 3-4 foot hole 1 ft. dia, then mixed up a batch of clay/sand/rock salt to pour in it...and wet it with water......said the salt will permeate further into the earth over time.......then used a 1" copper rod about 6ft long and drove it into it..then connected a large clamp to our incoming water pipe...then also continued the large wire to our incoming power box ground with another clamp on the conduit and box....

He said lightning now has a very good path into the earth....and any galvanic action between our water pipes and surrounding mineral deposits or other neighbors pipes will be minimal....there's might all corrode away, but ours wouldn't...??

We never had any problems...and my Crystal set radio with my 50ft antenna on the roof worked great too!!

I once was in Malta on a wooden ship which had a full copper plated bottom over the wood up to the water line...and any other ships docked nearby would have all its zinc anodes dissapear very fast....and any steel fittings/props etc. disolve away......very scary....big harbor battery's ha ha....

Copper rules.....

Now days there is actual meters which measure the electric current between the ships hull and surrounding water, and can inject electric current to diminish the galvanic action....helps kill marine growth too.... Having to drydock a large ship to clean hulls/replace zinc anodes isn't cheap.....electrolysis sucks -

Gerry

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There wouldn't be any power generated unless a magnetic field was CHANGING (cutting) thru your wire. The Nasa project was to see if they could change the orbit of the satellite and conversely induce a current (generate electricity) using a long wire and electricity.

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