Separate grounding system

[joshfromoshoto]

This may seem like a dumb question, but I am unable to test it. Will you read voltage from a hot leg, to a completely separate grounding system or neutral? My thought is say you were to drive a ground rod and not bond it to anything, if you were to put voltage to the ground rod it would not cause an arc nor would it likely trip any breaker, and from the hot leg to the ground rod you shouldn’t show any voltage. But if we take it further and have an entirely separate grounding system, not bonded at any point to the source voltage would the voltage read on a meter?


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[LarryFine]

You're asking about the effectiveness of earth as a conductive pathway.

A high-impedance voltmeter will read earth as a fairly good conductor.

A low-impedance tester or light will read earth as a terrible conductor.

Earth is such a poor conductor that it's not considered a parallel path.

 

[joshfromoshoto]

You're asking about the effectiveness of earth as a conductive pathway.

A high-impedance voltmeter will read earth as a fairly good conductor.

A low-impedance tester or light will read earth as a terrible conductor.

Earth is such a poor conductor that it's not considered a parallel path.

Im asking if there’s a potential difference between any 2 points or if the 2 points need to be part of the source.


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[LarryFine]

Im asking if there’s a potential difference between any 2 points or if the 2 points need to be part of the source.

Yes, definitely. Shock hazards while standing on the ground are an example of that.

Earth is conductive enough for there to be measurable current in a grounded system.

A hot wire from a grounded system will read voltage from any non-grounded point.

 

[joshfromoshoto]

Yes, definitely. Shock hazards while standing on the ground are an example of that.

Earth is conductive enough for there to be measurable current in a grounded system.

A hot wire from a grounded system will read voltage from any non-grounded point.

The shock hazard was the clearest way of explaining that. Thank you


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[suemarkp]

This may seem like a dumb question, but I am unable to test it. Will you read voltage from a hot leg, to a completely separate grounding system or neutral? My thought is say you were to drive a ground rod and not bond it to anything, if you were to put voltage to the ground rod it would not cause an arc nor would it likely trip any breaker, and from the hot leg to the ground rod you shouldn’t show any voltage. But if we take it further and have an entirely separate grounding system, not bonded at any point to the source voltage would the voltage read on a meter?

Yes you will. There were old "worm hunter" devices which were basically a lamp socket with a 120V power cord. The hot went to one side of the lamp and the ground/neutral were not used. The other end of the light bulb was connected to a copper pipe or wire and you shoved that into the ground and then plugged in the light. This caused current to flow in the earth and the worms don't like that so they come to the surface of the dirt.

My dad had one of these and I remember being on my hands and knees and sticking my finger into the dirt near that light rod. I could feel a tingle because of the voltage gradient in the earth between my knees and my finger. Current was going in all directions from that rod in the earth as it went to the house ground electrode, and every ground electrode on every power pole in the neighborhood to make it back to the house transformer neutral (the neutral on every house transformer is typically solid from pole to pole and pole to house, and each pole with a transformer typically has a ground electrode as does each house, so there are many paths back to any one transformer).

The purpose of the light bulb was to limit current, but it was probably unnecessary because of the resistance of that short rod to the earth. The earth is a weird conductor. It is great for long distances. The problem is where current is put into the earth and where it comes out -- that "insertion loss" can vary from a few ohms if they are close to 100 ohms or more at each electrode when they are about 50' apart. So two electrodes near each other may have 200 ohms of resistance rod to rod. Space them miles apart and it will still be near 200 ohms. The resistance of a ground electrode doesn't increase much at all after 25 feet from the electrode.

 

[electrofelon]

This may seem like a dumb question, but I am unable to test it. Will you read voltage from a hot leg, to a completely separate grounding system or neutral? My thought is say you were to drive a ground rod and not bond it to anything, if you were to put voltage to the ground rod it would not cause an arc nor would it likely trip any breaker, and from the hot leg to the ground rod you shouldn’t show any voltage. But if we take it further and have an entirely separate grounding system, not bonded at any point to the source voltage would the voltage read on a meter?


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I'm going to sort of disagree with the others and say that first we need to know whether the system with the hot leg you are talking about is grounded or not. If yes then I agree with post #2. If it's not grounded, then the answer is pretty much the same but this would be due to capacitive coupling and leakage.

 

[winnie]

A voltage can be defined between any two points, including points in free space or a point on an ungrounded system to a point on soil.

But your measurement instrument itself is part of the system and will change the voltage being measured.

Consider the entire circuit of source(s), impedances and meter impedance. If the meter impedance is larger then the over-all impedance of the circuit, then you will get a well defined voltage measurement.

The impedance of connections through soil might be anywhere from a couple of ohms to several thousand ohms. Soil is a poor conductor but there is quite a lot of it so the resistance of a path through the soil is dominated by the electrodes at the ends of the path.

Most digital meters have impedance ratings in the megohm or gigohm range; the impedance of the soil part of the circuit wouldn't change the measurement with such a meter.

Jonathan

 

[Jpflex]

This may seem like a dumb question, but I am unable to test it. Will you read voltage from a hot leg, to a completely separate grounding system or neutral? My thought is say you were to drive a ground rod and not bond it to anything, if you were to put voltage to the ground rod it would not cause an arc nor would it likely trip any breaker, and from the hot leg to the ground rod you shouldn’t show any voltage. But if we take it further and have an entirely separate grounding system, not bonded at any point to the source voltage would the voltage read on a meter?


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I have wandered this myself. Apparently current returns to the source. If two different generators are running, will voltage be seen from one phase leg of one generator to the neutral or phase leg of another generator.

I never tested this but logically to theory if grounds and neutrals have no connection between generators, there may be no voltage seen because current is not returning to ITS source as the voltmeter is connected in this way.

 

[joshfromoshoto]

I'm going to sort of disagree with the others and say that first we need to know whether the system with the hot leg you are talking about is grounded or not. If yes then I agree with post #2. If it's not grounded, then the answer is pretty much the same but this would be due to capacitive coupling and leakage.

So a hot leg of 120vac from an ungrounded system to another systems ground? In that case would you see 120v?


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[electrofelon]

So a hot leg of 120vac from an ungrounded system to another systems ground? In that case would you see 120v?


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You would likely read voltage if using a high impedance meter. If using a low impedance, probably not. Results will vary depending on how large the ungrounded system is and it's proximity to grounded objects.