Earth Shells Experiment = time to eat crow!

[dbuckley]

The really funky thing about earth electrodes is that eventually the resistance between the electrodes stops rising as the distance increases. For example USA to UK is about 500 ohms. This was discovered in the early days of telegraph cables.

And as Wayne notes above (and I've noted elsewhere) - you can pass thousands of amps for thousands of kilometers through the soily stuff providing you get your electrodes designed right: this is standard stuff for HVDC transmission.

 

[gar]

090802-1650 EST

hurk27:

I am not sure what you mean by MGN. I assume Multi Ground Neutral. But what does that mean? I my case it has nothing to do with with the primary other than thru any possible leakage from primary to secondary.

However, I have one neighbor that shares my transformer. Thus, we have MGNs between us, but nothing to the primary. Their main water pipe path back to ours is probably thru a 1.5 mile path. They are not home today and thus very little load. When I measured the voltage drop from their ground rod or meter box to our pole ground rod I read about 6 MV. My voltage drop from the same pole ground rod to my water pipe grounding point or conduit at entrance to my house has been under 50 MV with whatever loading I have on the system.

Earlier today when I did the 12 ft screwdriver measurement in line with the path from the pole to my meter I read about 12 MV. Presently I read about 8 MV for 12 ft, and 18 MV for 24 ft. This leaves about 6 ft on either side of the 24 ft span before I get to the pole or meter. These are approximate measurements based on using Fluke test lead lengths. I believe these are 2 meter leads and I do not pull tight. The voltage in this region of the yard seems to be defined by the pole ground rod and the house water pipe. The tape measurement from meter to pole is 34 ft.

.

 

[hurk27]

090802-1650 EST

hurk27:

I am not sure what you mean by MGN. I assume Multi Ground Neutral. But what does that mean? I my case it has nothing to do with with the primary other than thru any possible leakage from primary to secondary.

However, I have one neighbor that shares my transformer. Thus, we have MGNs between us, but nothing to the primary. Their main water pipe path back to ours is probably thru a 1.5 mile path. They are not home today and thus very little load. When I measured the voltage drop from their ground rod or meter box to our pole ground rod I read about 6 MV. My voltage drop from the same pole ground rod to my water pipe grounding point or conduit at entrance to my house has been under 50 MV with whatever loading I have on the system.

Earlier today when I did the 12 ft screwdriver measurement in line with the path from the pole to my meter I read about 12 MV. Presently I read about 8 MV for 12 ft, and 18 MV for 24 ft. This leaves about 6 ft on either side of the 24 ft span before I get to the pole or meter. These are approximate measurements based on using Fluke test lead lengths. I believe these are 2 meter leads and I do not pull tight. The voltage in this region of the yard seems to be defined by the pole ground rod and the house water pipe. The tape measurement from meter to pole is 34 ft.

.

I was only thinking of what other currents could be on the water pipe/MGN, as any houses could be connected down stream from your house (don't know if your at the end of the line) but any one of these houses or other loads could have a faulty neutral at the transformer, but still have a connection to the water pipe. This would allow current to run in the water pipe past your house to the next path back to the MGN then back to their transformer.

I have no idea why any stray currents would be trying to go to the water pipe in your area, unless there is a Y connected supply somewhere that is also returning current through the earth, in which I think we all have that to some extent.

 

[hurk27]

The really funky thing about earth electrodes is that eventually the resistance between the electrodes stops rising as the distance increases. For example USA to UK is about 500 ohms. This was discovered in the early days of telegraph cables.

And as Wayne notes above (and I've noted elsewhere) - you can pass thousands of amps for thousands of kilometers through the soily stuff providing you get your electrodes designed right: this is standard stuff for HVDC transmission.

there was never a correct measurement of power loss in the earth correctly recorded as far as I know of back in the early days of telegraph, even Tesla had it at about 100 ohms, and with the many newer SWER systems setting it at about .05 ohms, but the newer DC systems have now stated it more closer to the earth being 0 ohms over all, I still need to look up those papers I saw this in.

 

[don_resqcapt19]

...
And as Wayne notes above (and I've noted elsewhere) - you can pass thousands of amps for thousands of kilometers through the soily stuff providing you get your electrodes designed right: this is standard stuff for HVDC transmission.

I thought all of the HVDC transmission systems were 2 wire systems...no current in the earth.

 

[realolman]

So... this is not about the material from which the planet earth is made having zero ohms resistance, because your experiment clearly shows the soil to have impedance.

But... geometrically, there is an increasing area of conduction (number of paths) for current to flow through this soil that has impedance, the further you get from the energized pipe. (limited by the size of the world?)

So... Expanding upon the scope of crossman gary's experiment, the increasing number of paths in parallel sum up to a decreasing impedance, approaching zero.

And..... because the area of the soil conductor keeps getting smaller the closer you come to the energized pipe, it is a geometrical thing that most of the impedance that limits the current flow is closest around the energized pipe.

And... it'll work similarly on a ground rod where a fault current is involved.

So.. if we were to intall some sort of gigundo grounding electrode, such as crossman gary described at his facility, of water system pipes etc., we would increase the size of the conductor made of soil, and cut down on the resistance near the grounding electrode, merely because of conductive area.


Which ....would cause us to have to choose our GEC from Table 250.122 instead of just using a #6 or #4.


I think maybe I get it.

I may not be good, but I'm slow.

 

[crossman gary]

realoman:

That sounds exactly right to me. We both finally get it!

For the longest time, I was convinced that the high conductivity of my soil down here in Houston would have eliminated that "earth shells" thing. Then I finally went out and proved it to myself.

Now I'm a believer!

 

[realolman]

If I'm understanding this correctly now , I don't think I like the "earth shells" thing much.

I think the term stood in the way of my understanding.

It is an increasing of the area of the "soil conductor" as you move away from the ground rod.

One thing I don't think I grasp yet is that the farthest paths of current flow would also have the most impedance and would contribute the least to the total conductance of the path through the earth.

Even considering it as a 3D conductor, it seems to me the vast majority of current would flow in a relatively straight line to the other end of the transformer winding.

I'm not sure why points on the opposite side of the energized pipe would have much current flow or voltage at all.

 

[crossman gary]

Even considering it as a 3D conductor, it seems to me the vast majority of current would flow in a relatively straight line to the other end of the transformer winding.

I'm not sure why points on the opposite side of the energized pipe would have much current flow or voltage at all.

At first sight, that makes sense to me and that is exactly what I believed previous to my experiment. This belief is what persuaded me to drive only two pipes on the side of the rod away from the building. I figured that all of the current would be flowing directly to the building.

But then the voltage drops on the test pipes away from the building were about the same as those toward the building. Hmmmm....

Here is my explanation for that: Say that the test electrode is 150 feet from the building. There is a current path from the electrode directly to the building, and it is 150 feet long. There is another current path going out the back of the electrode, and then curving left for 180 degrees to get headed back toward the building. Say this curved portion has a 6 foot diameter. The extra length of this current path is Pi x 3 = approximately 9 feet.

So the path straight to the building is 150 feet, and the path out the back of the rod is 159 feet. This is only a 6% difference. If we do circuit calculations, we will find that current would indeed flow in the 159 foot path along with the 150 foot path. This is similar to 2 resistors in parallel, with one resistor being slightly higher resistance than the other.

I'm not sure it really and truly is this way, but it is certainly plausible. With the resistance of the huge circular mil area being so low, practically zero, the extra length probably hardly matters at all.

Hope this made sense.

 

[crossman gary]

and darn....

I just realized I made a mistake in the diagram in post 27.

I did not properly draw in the red circles representing the shells. The one foot circle crosses the 2 foot pipe on the backside of the electrode. Argh!

 

[realolman]

Hope this made sense.

It does now... thanks.... and thaks to Hurk as well.

 

[hurk27]

I thought all of the HVDC transmission systems were 2 wire systems...no current in the earth.

Don many of the HVDC systems are monopole (SWER) systems, the only time they cant use it is where is crosses water with heavy ship traffic, as the magnetic field messes up there compass.

Here is one such CABLE

and here is a list of both monopole and bi-pole HVDC cables

 

[hurk27]

If I'm understanding this correctly now , I don't think I like the "earth shells" thing much.

I think the term stood in the way of my understanding.

It is an increasing of the area of the "soil conductor" as you move away from the ground rod.

One thing I don't think I grasp yet is that the farthest paths of current flow would also have the most impedance and would contribute the least to the total conductance of the path through the earth.

Even considering it as a 3D conductor, it seems to me the vast majority of current would flow in a relatively straight line to the other end of the transformer winding.

I'm not sure why points on the opposite side of the energized pipe would have much current flow or voltage at all.

If we can accept, that the Earth is over all at 0 ohms outside of the Sphere of Influence, then it starts to make sense, since at 0 ohms current will flow equally in all directions distance no longer matters, it will flow all the way around the globe to get back to the x-0 of the transformer, does this really happen, well it would seem it would, if the earth is in fact 0 ohms, but I haven't located the papers form the university, I saw them on. (I'm still looking)

this is also what I was telling Gar in post 34 and post 37.

it would be like trying to find the direction of a radio transmitter, standing upon the other side of the globe, the signal would seem to come from all directions.


Here's another way to think about this, if you were to continue Gary's shells to the point of no more voltage change, in theory about 25', and outside of this circle you place the earth at 0 ohm's then we can see why the current flows evenly in an outward direction, and at 0 ohms it would be just like having the x-o of the transformer being all around the SOI.

 

[crossman gary]

Here's another way to think about this, if you were to continue Gary's shells to the point of no more voltage change, in theory about 25', and outside of this circle you place the earth at 0 ohm's then we can see why the current flows evenly in an outward direction, and at 0 ohms it would be just like having the x-o of the transformer being all around the SOI.

Now that is a good way to put it. Makes sense.

As long as the building electrode system is large and has good conductivity, then the actual potential at 25 feet would be close to being at the Xo potential as you say.

 

[dbuckley]

there was never a correct measurement of power loss in the earth correctly recorded as far as I know of back in the early days of telegraph, even Tesla had it at about 100 ohms, and with the many newer SWER systems setting it at about .05 ohms, but the newer DC systems have now stated it more closer to the earth being 0 ohms over all, I still need to look up those papers I saw this in.

Far as I can tell Tesla was never a big name in telegraph. If I've read it correctly, the evolution of the Ohm as a unit of measurement happened almost as a consequnce of trying to faultfind telegraph lines by measuring the resistance of the line, but its a bit hard to discuss the issue when everybody's tools were "calibrated" in different units.

Kimbark in "Direct current transmission" states that the resistance between two earth electrodes is independent of the distance between the electrodes, once you get them far enough apart. I'm sure I got my 500R number from somewhere reputable but cant find a reference now, so maybe I did dream up the number But certainly once you get a decent distance then then number stays the same, and I've seen it suggested that you can just assume the path resistance to be the sum of the two electrode resistances.

 

[hurk27]

Just thought of something

If the Earth is not 0 ohms, we would have a problem with all the current flowing through it, resistance equals heat, and the current would be causing global warming

so I sure hope its 0 ohms:grin:

 

[perry vogler]

Experiment

Experiment

Not tring to be funny but I don't understand the finding of your experminet. We know that currents flow through the earth, the the soil depending on its contents has different levels or conductivity or resistance. Of cource you will get a voltage drop with the experment. You will also be able to get an amp reading as well to tell how many watts were consumed. This is why we bond metal parts, pool decks and agraculture buildings. Can you clarifie please? thanks, Perry

 

[hurk27]

Not trying to be funny but I don't understand the finding of your experiment. We know that currents flow through the earth, the the soil depending on its contents has different levels or conductivity or resistance. Of course you will get a voltage drop with the experiment. You will also be able to get an amp reading as well to tell how many watts were consumed. This is why we bond metal parts, pool decks and agriculture buildings. Can you clarify please? thanks, Perry

Basically this thread was started because of this thread: Ground Rod at a construction trailer Y or NO

you have to read the whole thing to show how it evolved, but simply it was about the question of what safety can a ground rod provide, if there is no EGC to a trailer, and the subject wound up on the voltage drop or touch potential from a rod.

In the end it was proved that a ground rod provides no such protection, based upon the reason in the results of the test.

it is not the conductance of Earth that is a problem, because the Earth over all has no resistance 0 ohms, this is because of the amount of parallel paths the current can take and this includes circling the globe.

The problem is our connection to the Earth, since in the first few feet from the rod there is not much soil around the rod, so the resistance is high, so the voltage drop happens within the first few feet. @ 3' from the rod you will drop 75% of the voltage, so a person kneeling down next to a rod energized at a 120 volts will receive a 90 volt shock if his knee is 3' from the rod.

In Gary's experiment his soil has the capability to open a 15 amp breaker, this is because of the high carbon content of his soil, but even with this good soil , it still didn't reduce the touch potential surrounding the rod, and increased it, if anything by making the 90 volt shell smaller.

remember we were applying a voltage to the rod to simulate a hot to ground fault in a trailer that didn't have a proper EGC connected to the frame.

Bottom line is without an EGC bonded to the frame of the trailer, a ground rod will not protect a person if a hot to frame fault was to occur.

This is an area that many electrician's and even electrical engineers don't understand fully, and we see it in some of the request on spec sheets for ground rod's:roll:

 

[marti smith]

This is the very reason I use this site. Wonderful information and a great compilation of knowledgeable minds to obtain information from. You all have no idea how much help you are to the industry. Thank you.

 

[LarryFine]

You all have no idea how much help you are to the industry.

Sure we do!