Earth Shells Experiment = time to eat crow!

[crossman gary]

I did the following experiment this afternoon just to prove to myself what was the real deal about the voltage drops around a driven electrode.

I had assumed that the low resistance of the soil in my area would have prevented much of a voltage drop in the "earth shells" around the electrode - and stated as much in the "construction trailer - ground rod" thread located here:

http://forums.mikeholt.com/showthread.php?t=114269

Here is a photo and a diagram of my results based on the following: My power source was 50 volts 60Hz AC and this was pushing 6 amps through the hot wire to the 5 foot deep pipe into the earth. I didn't use 120 volts because it would have tripped the OPCD of my supply as evidenced in previous experiments which are documented elsewhere on the forum.

Soil conditions were moist, must have had some rain in the past few days as there was a bit of standing water in the ditches in the area. (I was out of state last week so I don't know if it rained but it must have)

If we want to consider 120 volts instead of the 50 volts, we can just multiply the voltage drops by the ratio 120/50.

Note: The pipe driven at 1 foot from the electrode was put in after I took the photo.

I was very surprised to see such a high voltage drop around the pipe! I was almost in disbelief.... I was using a digital meter, so then I did the same measurements with a Simpson. Same results. Wow. So in my head I am thinking this has to be some kind of "ghost voltage/capacitive something" due to the high impedance of the meters.

So I took a small 24 volt indicator lamp, attached some leads, and put it across the electrode to the 1 foot pipe. It lights up brightly! Wow again.

I carefully disconnected the hot wire from the electrode and there was a discernible spark. I measured the voltage from the hot wire to the electrode and of course it measured 50 volts.

So okay, well, the test pipes are driven in 1 foot. What if we wanted to see what would happen if a person walked barefoot in the area? We took the digital meter, held one lead on the electrode, and then simply placed the other lead down in the grass... bingo... just about the same voltage readings as the test pipes. Wow again.

Anyway, there ya go. Nothing like actually performing the experiment to make a believer out of you (me).

Conclusion: In the experiment with the hot wire detached from the electrode, there was a 50 volt shock potential. With the electrode attached, the shock potential was lessened a little, 33 volts at 1 foot from the electrode, 41 volts at 2 feet away, and increasing.

While an electrode most likely will lower the shock potential from an energized object, it certainly will not nullify the entire potential. The EGC is absolutely the most important item for safety ( I always believed this, and would never rely solely on the electrode. I admit that I believed the electrode would have done a lot more to eliminate the potentials in the area.)

Moral:

1) Follow the Code!
2) This was a great learning experience.
3) Crow doesn't taste all that bad really.

 

[roger]

Gary, you are an outstanding forum member

, and even though you are presently an instructor in an apprenticeship program, you should be training journeymen and masters.

Wait, you are here.

Roger

 

[crossman gary]

Roger, I am blushing at such a terrific comment. That is the most complimentary thing I have heard in a long time.

Thank you!

I'm just a humble guy who loves to know why things work as they do... and I typically like to learn first hand, if not by actual experimentation, at least by deep and contmplative thought. And of course, it certainly helps to have everyone here at MHF to help me along.

Thanks again Roger. You made my day.

Gary

 

[quogueelectric]

Your posts are fantastic and very informative I totally applaud your efforts to post such informative presentations. I would add it is not easy to clap with hooves.

 

[hurk27]

It's great when we see the results that before didn't make sense, now you know that the Earth has more leverage to maintain, the reference voltage
X-0 then the rod can, and as you got to the 6' mark, it started to level out, as you saw with the same reading at 8' this because your out of the SOI (sphere of influence), and the voltage curve will flatting out as the farther you get from the injection rod.

I do think I did get it backward though, with better soil the SOI is smaller , and with higher resistance soil it is bigger.

this experiment is just like a long cord with one 16 AWG conductor on the hot, and one 12 AWG conductor on the neutral, with a dead short at the end, the earth is the #12 and your injection rod is the #16 with your test points placed along the #16 at intervals from the suply end.

Measuring from the supply to each point along the #16 will give you a higher reading as you go towards the end or where the short is.

I wish I had the space and time to preform shuch exerments, but with a yard full of copper pipe sprinkler system and no where to get away from it, it would be hard.

Great job, this is somthing we all can learn from

 

[hurk27]

oh and at 120 volts this should be close to your results:

@ 1' 66% drop 79.2v
@ 2' 82% drop 98.4
@ 4' 88% drop 105.6
@ 6' 92% drop 110.4
@ 8' 92% drop 110.4 v

 

[SEO]

Very informitive post Gary.

 

[ultramegabob]

I just have one question.... did you pick up the earthworms to use for bait while you were doing this experiment?:grin:

 

[crossman gary]

Your posts are fantastic and very informative I totally applaud your efforts to post such informative presentations. I would add it is not easy to clap with hooves.

Thank you kindly.

I have been thinking about the results, and I think I have a reasonable explanation as to why the voltage drops work like they do. As soon as I get a chance to draw another diagram, I will post my ideas for the rest of you to consider and comment on.

 

[crossman gary]

It's great when we see the results that before didn't make sense, now you know that the Earth has more leverage to maintain, the reference voltage
X-0 then the rod can, and as you got to the 6' mark, it started to level out, as you saw with the same reading at 8' this because your out of the SOI (sphere of influence), and the voltage curve will flatting out as the farther you get from the injection rod.

I definitely learned something!

I do think I did get it backward though, with better soil the SOI is smaller , and with higher resistance soil it is bigger.

The same thing crossed my mind.... but with other things equal, doesn't that mean that a person on the good soil will get a greater shock than the person on poor soil? Man, that just doesn't sound right, but apparently it is.

this experiment is just like a long cord with one 16 AWG conductor on the hot, and one 12 AWG conductor on the neutral, with a dead short at the end, the earth is the #12 and your injection rod is the #16 with your test points placed along the #16 at intervals from the suply end.

Measuring from the supply to each point along the #16 will give you a higher reading as you go towards the end or where the short is.

That is very similar to the thoughts I had when trying to understand the results. The earth in the vicinity of the electrode is actually acting as the "load resistance" between a low resistance hot wire and a low resistance return path. The small amount of earth area around the rod has a higher resistance than the humongous area of earth at further distances. it seems obvious now that most of the voltage drop is going to occur at the higher resistance load rather than be spread out equally along the entire series path through the earth. Thanks for the analogy you made above.

As I type, I remember that Iwire had this discussion with me a couple of years ago right here on the forum. He explained all this but apparently I forgot, or I was not exactly convinced. Well, I am now. So my apologies to Bob for not listening back then!

I wish I had the space and time to preform shuch exerments, but with a yard full of copper pipe sprinkler system and no where to get away from it, it would be hard.

if you have any ideas, shoot them at me, maybe I can do the experiments for you.

 

[hurk27]

The quote below is from the one link I posted in the other thread HERE
It give a good reason as to why this happens.

Resistance and Distance from an Electrode
Around an earth electrode the resistance of the soil is the sum of series resistances of virtual shells of earth propagating outward from the electrode. Shells nearest to the electrode have the smallest surface area and hence the largest resistance.

And here is a chart of the voltage curve to distance from the rod

 

[crossman gary]

SEO: Thank you

Ultramegabob: I haven't seen any earthworms yet, and I have done about four of these types of experiments in the last 2 weeks.

 

[crossman gary]

Hurk,

It all makes so much sense now. So why didn't I believe it when other people kept telling me??

I was still trying to apply a nice equal series resistance from the experiment pipe electrode all the way back to the building electrode, with the voltage drop being equally spread out along the entire path.

 

[hurk27]

Hurk,

It all makes so much sense now. So why didn't I believe it when other people kept telling me??

I was still trying to apply a nice equal series resistance from the experiment pipe electrode all the way back to the building electrode, with the voltage drop being equally spread out along the entire path.

It's kind of hard to understand the electrical phenomenon, in a 3 dimensional view when we are used to looking at it just two dimensions. I learned this at FSU doing lightning studies and it took me by surprise too, What also surprised me was that the over all resistance of the Earth globe is 0 ohms, this has been proved by calculating the power losses in a 500kvdc SWER transmission cable, all the losses were accounted for in the cable and connection point to earth, so the only answer was that the rest of the earth was 0 ohms the perfect conductor, the problem we have is our very small connection point.

 

[ultramegabob]

Ultramegabob: I haven't seen any earthworms yet, and I have done about four of these types of experiments in the last 2 weeks.

That kind of suprizes me, when I was a kid, my dad had a hand cranked generator out of an old wooden phone. We used to hose the yard down for a few minutes and stick a couple of wires down into the ground and give it a few cranks and they would pop up like crazy:grin:

 

[crossman gary]

so the only answer was that the rest of the earth was 0 ohms the perfect conductor, the problem we have is our very small connection point.

And that is exactly it. It is so darned obvious now. And that small connection point is essentially a load and that is where the majority of the voltage is dropped.

It feels great to have finally wrapped my brain around this!

 

[crossman gary]

That kind of suprizes me, when I was a kid, my dad had a hand cranked generator out of an old wooden phone. We used to hose the yard down for a few minutes and stick a couple of wires down into the ground and give it a few cranks and they would pop up like crazy:grin:

I think the explanation is that the clay soil we have doesn't have that much organic matter in it. If I was to dig in it, I wouldn't find that many worms. They tend to congregate in the flower beds and gardens where fertilizer and organic stuff has been added.

Ay my previous residence, I had a fair sized garden and a big compost heap of leaves and grass clippings, table scraps, etc. Now THAT is where the humongous earthworms were!

 

[iwire]

The EGC is absolutely the most important item for safety ( I always believed this, and would never rely solely on the electrode.

I know that I had never gotten the impression from you that the EGC was not important.

3) Crow doesn't taste all that bad really.

I don't see where you have any crow to eat. You had some ideas that you took the time to research.

Gary, you are an outstanding forum member

, and even though you are presently an instructor in an apprenticeship program, you should be training journeymen and masters.

Wait, you are here.

Roger

I would like to second Rogers comments.

 

[Dennis Alwon]

Thanks Gary , I too would like to third Rogers comment even tho some of this is over my little head. We all appreciate the energy you have to do the experiment and then to report back.

Eating crow is not that bad.... I do it regularly around here. :grin:

 

[realolman]

the rest of the earth was 0 ohms the perfect conductor, the problem we have is our very small connection point.

I don't see then why the voltage drops are different at the stakes farther away from the deeper "energized" rod, since all the stakes should have the same "small connection point" resistance