Let's say we have a 120 Volt AC source

[Evil Bunny]

Trying this again from a different angle...

Let's say we have a 120 Volt AC source. We'll call it a generator. This generator is not touching the earth. Let's just pretend that it's suspended in mid air with nothing at all connecting it to the ground (the earth). On this generator, there are two poles. If you put a volt meter across the two poles of the generator, your meter reads 120 Volts.

You attach a wire to one of these poles, leaving the other one alone with nothing attached to it. You stick the other end of that wire into the earth. Does current flow?

Why or why not?

 

[Feldoh]

Depends on what you're referencing as your 0 volt point.

To clarify if there is a ( nonzero) potential difference between the ground and your "hot" line there will be an electric field, this electric field will cause electrons to flow thus generating a current.

 

[Evil Bunny]

Depends on what you're referencing as your 0 volt point.

To clarify if there is a ( nonzero) potential difference between the ground and your "hot" line there will be an electric field, this electric field will cause electrons to flow thus generating a current.

The only reference in this scenario is the other pole. The Earth is not referenced anywhere in this electrical circuit. If one meter lead is on a pole and the other meter lead is on the other pole, your meter reads 120V.

I contend that if you put one meter lead on a pole (doesn't matter which one) and the other meter lead in the earth, you will read 0 Volts. Do you agree?

 

[Feldoh]

If your reference is the "other pole" then you would need to measure the voltage difference between the ground and the "other pole" and from there you could find the potential difference between the ground and the "first pole".

The ground still might have a potential difference but you'd ned to reference it with the "other pole".

The voltage at a single point is entirely relative and meaningless the only that is physical is a difference in voltage between two points.

Ask yourself where the notion of potential difference come from. They arise because of electric fields. Electric fields carry energy and if we do work to place two charged particles at two different distances they will have two different potentials. It's the same if we are to lift two objects to two different heights there is a potential energy difference in the two objects.

 

[Evil Bunny]

If your reference is the "other pole" then you would need to measure the voltage difference between the ground and the "other pole" and from there you could find the potential difference between the ground and the "first pole".

The ground still might have a potential difference but you'd ned to reference it with the "other pole".

The voltage at a single point is entirely relative and meaningless the only that is physical is a difference in voltage between two points.

Ask yourself where the notion of potential difference come from. They arise because of electric fields. Electric fields carry energy and if we do work to place two charged particles at two different distances they will have two different potentials. It's the same if we are to lift two objects to two different heights there is a potential energy difference in the two objects.

I understand that voltage is a potential difference between two points... If you're talking about a "reference" then you're talking about either pole A or pole B, correct? What else could the reference possibly be? I'll just pick one for the sake of moving forward. Our reference is now pole A. You would measure a potential difference between the "reference" (pole A) and another point. I'm saying that the potential difference between the two poles is 120 Volts. The potential difference between pole A and the Earth is 0 Volts. The potential difference between pole B and the Earth is also 0 volts. Is there disagreement on this or not? If you are saying there is a voltage present there, can you explain why?

 

[cepheid]

I'm saying that the potential difference between the two poles is 120 Volts. The potential difference between pole A and the Earth is 0 Volts. The potential difference between pole B and the Earth is also 0 volts. Is there disagreement on this or not? If you are saying there is a voltage present there, can you explain why?

Let's say that V_A is the electric potential at pole A, V_B at pole B, and V_Earth of the earth, all measured relative to some common reference point.

So you're saying that

V_A - V_B = 120 V

but

V_A - V_Earth = 0 V

AND (somehow!)

V_B - V_Earth = 0V

You see that this is impossible, right? If pole A and pole B are not at the same potential, then they can't BOTH have the same potential relative to Earth.

If, for the sake of argument, V_B = V_Earth, then it must follow that V_A - V_Earth = 120 V (NOT 0 V)

So, in this example, if you connected pole A to Earth, current would flow, since pole A has a positive potential relative to Earth.

 

[cepheid]

I understand that voltage is a potential difference between two points... If you're talking about a "reference" then you're talking about either pole A or pole B, correct? What else could the reference possibly be?

It could be ANYTHING you want. Pick a point in space, and define the electric potential to be zero there. All other electric potentials are measured relative to the potential at this point. This point is called "ground" or "earth" in a circuit, but it doesn't necessarily have to be physically connected to the Earth.

Obviously it's convenient for this situation if the reference point is one of the poles in the voltage source.

 

[Evil Bunny]

You see that this is impossible, right? If pole A and pole B are not at the same potential, then they can't BOTH have the same potential relative to Earth.

This may be true. In fact, I ventured into a physics forum and everyone here is waaaay smarter than me and you certainly sound like you know what you're talking about, so I will concede that it is in fact true. I was wrong.

But I think this difference is extremely small and probably hard to measure with common instruments. Let's say that your volt meter doesn't have a decimal point and it is accurate to only the nearest volt. I bet the display on your meter reads 120 Volts between the poles and 0 Volts between either one of the poles and the earth. Do you disagree with that?

If we can't agree on that, let's change the example to something we can test easily ourselves. Let's get a battery and a volt meter and take some measurements. A car battery would be best, but we can use a little 9V battery for simplicity. If you measured voltage across the (+) and (-) terminals of the battery you would get the battery voltage (assuming it was charged of course). I bet we all agree on that.

Now for the meat of it... I contend that you will get 0V if you measure between either one of the battery terminals and the Earth (lets make sure the battery is isolated from the earth. If you can't levitate it, then I guess you could put it on a piece of wood or a wooden table or something to make sure there is no connection being made from the Earth to either terminal ). Stick one lead on the positive terminal and the other lead into the earth. What does your meter display? Now move the lead from the positive terminal to the negative terminal of the battery, (leaving the other lead stuck in the earth) what does your meter display?

I contend your meter will display 0 Volts. Try it and let me know please...

I would try this myself, but the Earth around me is frozen solid with 3 feet of snow on top of it. However, I did try it in my house with my meter and a AA battery. My results were 1.6V between the terminals and 0V from either terminal to my tile floor. That's the best I could do.

Does anyone disagree that this would be the case? If there is no disagreement on this, can we go back to the original post and pick up where we left off? If there is disagreement on this, let's see if we can get to the bottom of it.

 

[Naty1]

Does current flow?

no..you need a complete circuit...a connection to the other pole...

 

[Evil Bunny]

no..you need a complete circuit...a connection to the other pole...

Thank you!

Okay... Now here is my question:

I'm confused on "charge" I think. Electrons will always want to equalize. Correct? If there is a more positive charge on pole A with respect to pole B and there is a way to get there, the electrons will want to equalize and current will flow.

Doesn't this mean that there is a deficiency of electrons on the positive pole?
Doesn't this also mean that there is an overabundance of electrons on the negative pole?

If there is a deficiency of electrons on the pole and you touch that pole to the Earth (with a wire perhaps), why aren't the electrons from the Earth being attracted to the pole with the deficiency?

Is it because they are "equalized" in the Earth already and they just want to hold on tight to where they are? It seems to me that if you had enough of a deficiency of electrons on that pole. the electrons in the Earth would eventually be attracted to it and move there.

But then we'd measure a voltage. So I just don't get it... I feel like I'm really close to understanding this but it's still escaping me.

I'm pretty certain that I'm confusing charge and voltage and using them interchangeably when I shouldn't be... Or something.

 

[Naty1]

"...I'm pretty certain that I'm confusing charge and voltage and using them interchangeably when I shouldn't be..."

I can still remember trying to figure out the difference MANY years ago...most people have to think about each for a while when first confronting them...keep going and it will make sense sooner than you probably think...

Try reading here:
http://en.wikipedia.org/wiki/Electric_current

charge (q) is measured in coulombs...a quantity of electrons...and current is charge flow per unit time...q = i t...

Voltage is often described by analogy using water: it's the analog to water PRESSURE...more pressue makes water flow faster, move more volume of water and VOLTAGE pushes electrons HARDER...more current and charge will flow...
V (or E) = IR...so for more voltage e or V for a given resistance, more current (I) is moved because there is greater ENERGY pushing each electron.

try here for voltage:
http://en.wikipedia.org/wiki/Voltage

 

[Naty1]

If there is a deficiency of electrons on the pole and you touch that pole to the Earth (with a wire perhaps), why aren't the electrons from the Earth being attracted to the pole with the deficiency?

very good question...I'm not sure I have a one sentence answer.

The the electric potential in your statement has moved all the electrons it can...they are stuck in place...if you connect just one wire, no electrons will move...because the charge that can be moved already has been...further movement is opposed by the electrons and voltage potential in place...


If the voltage difference is high enough current CAN flow even without ONE wire...that's what happens in a lightning storm when one part of a cloud is positive and another part is negative...

Are you familiar with a capacitor?, where equal charge is stored on either side of, say, parallel plates?...it's the electrical equivalent of what you example. Connecting either side to ground, individually, does NOT remove any charge from either side...electrons on the negative side (ungrounded) will oppose any more electrons being added if the positive side is grounded...in other words, the potential (voltage difference) won't change until a closed circuit is available...

 

[cepheid]

This may be true. In fact, I ventured into a physics forum and everyone here is waaaay smarter than me and you certainly sound like you know what you're talking about, so I will concede that it is in fact true. I was wrong.

I'd prefer it if you understood it, rather than just conceding the point, which tells me, "I wasn't convinced by your argument, so I'll just let it go." It would be a shame if you did that, because what you're saying is not impossible because of some hard-to-understand physics that I know and you do not. What you are saying is simply a mathematical or logical impossibility. You know arithmetic, therefore, you should be able to understand my argument. It stems from this:

If x = y

and,

y = z

then it must be true that:

x = z

Do you agree? Otherwise we have a logical contradiction. The same contradiction occurs in your scenario. You state that:

potential of pole A = potential of ground (because you measure no difference between them) [1]

And also potential of pole B = potential of ground [2]

From this it MUST follow that:

potential of pole A = potential of pole B.

Since A and B clearly do not equal each other (it was GIVEN that they differ by 120 V in our example), statement [1] and statement [2] cannot BOTH be true. In particular, if one of the poles has the same potential as ground, then the other one MUST differ from ground by 120 V, since the other pole differs from the first pole by 120 V.

But I think this difference is extremely small and probably hard to measure with common instruments. Let's say that your volt meter doesn't have a decimal point and it is accurate to only the nearest volt. I bet the display on your meter reads 120 Volts between the poles and 0 Volts between either one of the poles and the earth. Do you disagree with that?

Yes, I disagree, because, physics aside, it is a logical contradiction. (see above)

If we can't agree on that, let's change the example to something we can test easily ourselves. Let's get a battery and a volt meter and take some measurements. A car battery would be best, but we can use a little 9V battery for simplicity. If you measured voltage across the (+) and (-) terminals of the battery you would get the battery voltage (assuming it was charged of course). I bet we all agree on that.

Now for the meat of it... I contend that you will get 0V if you measure between either one of the battery terminals and the Earth (lets make sure the battery is isolated from the earth. If you can't levitate it, then I guess you could put it on a piece of wood or a wooden table or something to make sure there is no connection being made from the Earth to either terminal ). Stick one lead on the positive terminal and the other lead into the earth. What does your meter display? Now move the lead from the positive terminal to the negative terminal of the battery, (leaving the other lead stuck in the earth) what does your meter display?

I contend your meter will display 0 Volts. Try it and let me know please...

I don't need to try it. Once again, we've started with the premise that the potentials of the + terminal and the - terminal differ by +9 V. Therefore, whatever you measure as the difference between the potentials of the - terminal and ground, the difference between the + terminal and ground HAS TO be 9 V higher than that. Otherwise, it would contradict our premise that the + terminal is 9 V higher than the - terminal.

So, if you measure the difference between the - terminal and ground, and you happen to get 0.00512 V (5.12 millivolts), then the voltage between the + terminal and ground MUST be 9.00512 V (otherwise the difference between the terminals would not be 9 V). I really hope that you see that this must be true.

I would try this myself, but the Earth around me is frozen solid with 3 feet of snow on top of it. However, I did try it in my house with my meter and a AA battery. My results were 1.6V between the terminals and 0V from either terminal to my tile floor. That's the best I could do.

Yeah, but that's because your tile floor is an insulator, and so the probe of the meter is not at the same potential as the floor. If you don't believe me, then let me ask you this: what does your meter read when neither of the probes is touching anything (or each other)? In other words, the voltage between the probes is "floating" (because the probes are not electrically connected and each one's potential could change independently by small amounts). I bet it displays 0 V as a default value. That's what my cheapo multimeter displays when the voltage between the probes is floating.

EDIT: Or it could be that any initial imbalance in potential between the two probes is equalized by the flow of charge from one probe to another. Since the second probe is not connected to anything that can sink charge, those charges have nowhere to go and "pile up", balancing out any initial differences in potential.

When we talk about "Earth", we mean something that acts like an ideal conductor (something that can be the source of or the sink for an arbitrary amount of charge without changing its electric potential). You'd have to dig a probe into the ground to get behaviour anything like that. Or you could just try measuring the voltage at each end of your battery relative to some conductor.

EDIT 2: No, that probably won't work for any finite conductor, because of what I said in my first EDIT. Charges can flow freely between the two conductors until their potentials have equalized. But it will work in theory for any point that has a definite and constant potential and is not free to "float" up to some higher potential through the transfer of charge..

 

[cepheid]

no..you need a complete circuit...a connection to the other pole...

Are you sure though? In this thread

https://www.physicsforums.com/showthread.php?t=469342

the OP had a similar question, and people were telling him that since the Earth can sink a LOT of charge without changing its potential, it could be very dangerous for a person to touch the positive terminal of a high voltage power supply. That person would be providing a path to ground for current, and the voltage across him would be maintained. Since the charges don't "pile up", there is no build up of an electric field to cancel out the one driving the current. In other words, there is no equalization of potential (this being the reason why current normally won't flow if there isn't a closed circuit).

Are they wrong?

EDIT: It looks like YOU were the one making this assertion, among others. So now I'm confused as to what your opinion is.

 

[Evil Bunny]

The the electric potential in your statement has moved all the electrons it can...they are stuck in place...if you connect just one wire, no electrons will move...because the charge that can be moved already has been...further movement is opposed by the electrons and voltage potential in place...

So I guess this is what I need to digest. I've got to process this for a little while.

I do have a solid understanding of voltage and that if you had enough of it the air would conduct and you'd have an arc. I also understand capacitors and how they work in electronic systems...

But I've been having detailed discussions about grounding and bonding of electrical systems and the way we distribute electricity in the united states. It's all about going back to the source. This is where most people (even electricians) go wrong... People think electrons want to make their way back to the earth. They do not. The only reason they EVER want to go into the Earth in the first place is because we drive large metal rods into the Earth with the specific intention of making the Earth part of the circuit, giving it a way to get back to the source.

I just keep getting hung up on this notion that if there is a large deficiency of electrons on a wire, the electrons in the Earth will still never be attracted to it, no matter what the voltage is. With enough voltage applied, the arc would be between the two poles of the source and never between the Earth and a pole. It's counterintuitive to me. But thanks for your answers, I will think on it some more.

 

[Studiot]

I just keep getting hung up on this notion that if there is a large deficiency of electrons on a wire, the electrons in the Earth will still never be attracted to it, no matter what the voltage is. With enough voltage applied, the arc would be between the two poles of the source and never between the Earth and a pole. It's counterintuitive to me. But thanks for your answers, I will think on it some more.

You just have to watch nature at work in the heavens to see how wrong this view is. Old Ben Franklin must be turning in his grave.

I think everyone will recognise that you can witness large discharges both between the clouds (poles) and the earth.

People think electrons want to make their way back to the earth

Unlike Arial in the Tempest, electrons do not posess desire, which implies free will and choice.

 

[Evil Bunny]

If x = y

and,

y = z

then it must be true that:

x = z

Do you agree?

I agree. I understand the logic and the contradiction you speak of. I also know how to read a volt meter and I trust that it is giving me the correct voltage.

So, if you measure the difference between the - terminal and ground, and you happen to get 0.00512 V (5.12 millivolts), then the voltage between the + terminal and ground MUST be 9.00512 V (otherwise the difference between the terminals would not be 9 V). I really hope that you see that this must be true.

I really hope that you go try it. This is not a true statement.

When we talk about "Earth", we mean something that acts like an ideal conductor (something that can be the source of or the sink for an arbitrary amount of charge without changing its electric potential). You'd have to dig a probe into the ground to get behaviour anything like that. Or you could just try measuring the voltage at each end of your battery relative to some conductor.

When I talk about earth, I am talking about the thing that my shoe touches when I walk outside. How about instead of the Earth we use... umm... your car? the ground rod under your meter box? Use whatever you want. I still say your voltmeter reads zero unless your meter is touching both ends of that battery. (again... no decimal point. meter rounds to the nearest volt)

 

[mquirce]

People. be patient uith a ignorant lay man.
I have a question about static electrisity and Plank quanta "h'
Let supose we have two electric unity charges far from each other 3.48181805*10^7 cm in static standing. The potential enrgy of these two charges will be E = h/1 erg.
Now let supose that distance is plus 10 cm longer. I am confused about dilema:
will be energy E< h/1 or will be 0 ?
Please somebody help!

 

[Evil Bunny]

You just have to watch nature at work in the heavens to see how wrong this view is. Old Ben Franklin must be turning in his grave.

I think everyone will recognise that you can witness large discharges both between the clouds (poles) and the earth.

You bring up a good point Studiot. Why is it that neither of the poles in our 120 Volt generator have any desire to interact with the Earth whatsoever, yet the electrons in that cloud are so excited to get to Earth that they ionize the air and we see a bolt of lightning come down and touch the ground?

Is it a matter of voltage? Let's take our suspended generator and crank it up to a million volts instead of just a wimpy 120 volts. Would that arc jump from one pole of the generator to the Earth or would it jump from one pole of that generator to the other? I've got my money on the one-pole-to-the-other option. What about you?

Excellent, excellent point! Something I know nothing about but am very interested in... Thank you.

Unlike Arial in the Tempest, electrons do not posess desire, which implies free will and choice.

 

[Naty1]

the OP had a similar question, and people were telling him that since the Earth can sink a LOT of charge without changing its potential, it could be very dangerous for a person to touch the positive terminal of a high voltage power supply. That person would be providing a path to ground for current, and the voltage across him would be maintained. Since the charges don't "pile up", there is no build up of an electric field to cancel out the one driving the current. In other words, there is no equalization of potential (this being the reason why current normally won't flow if there isn't a closed circuit).

Are they wrong?

Extremely high voltages have their own "set of rules"...try reading about lightning for example. I was recently told by a power company linesman they can use fiberglas poles up to something like 7,500 volts...don't quote me on that figure...so current might flow through their bodies otherwise..."What about 25,000 volts and even 250,000 volts...I asked" "how do you work on that"...answer..." You have to shut the power off...

 

[Naty1]

Take a dry cell battery as an example...1.5volts or maybe a 9 volt...touch one terminal the earth...even a car battery...12 volts...what happens??

nothing.

Now take wires stuck into the earth...say wet Earth and not too far apart...and touch them to the battery terminals...sparks almost certainly...current FLOWS...

 

[Naty1]

Try reading here:
http://en.wikipedia.org/wiki/Van_de_Graaff_generator

Note that a sphere holds electric hcarge quite well...one reason lightning arrestors...designed to AVOID charge build yup are typically pointed or wire brush like...to dissipate leader charges as quickly as possible.

 

[Naty1]

Bunny:

I ventured into a physics forum and everyone here is waaaay smarter than me

not likely...more experienced, perhaps...

Never think some else is smarter just because they understand something they have thought about and studied and you are just learning...

 

[JaredJames]

People. be patient uith a ignorant lay man.
I have a question about static electrisity and Plank quanta "h'
Let supose we have two electric unity charges far from each other 3.48181805*10^7 cm in static standing. The potential enrgy of these two charges will be E = h/1 erg.
Now let supose that distance is plus 10 cm longer. I am confused about dilema:
will be energy E< h/1 or will be 0 ?
Please somebody help!

You need to post this in a new thread, not hijack someone elses.

 

[Studiot]

Is it a matter of voltage? Let's take our suspended generator and crank it up to a million volts instead of just a wimpy 120 volts. Would that arc jump from one pole of the generator to the Earth or would it jump from one pole of that generator to the other? I've got my money on the one-pole-to-the-other option. What about you?

I thought my poetic cloud example would make it clear that both would likely occur.

Sorry if this was not clear.

 

[Evil Bunny]

I thought my poetic cloud example would make it clear that both would likely occur.

Sorry if this was not clear.

That's ok. No problem. Can you explain? I think if we slowly increase the voltage until it reaches a point to where an arc would form, this arc would travel from one pole to the other.

Are you saying that when this arc occurred, it would jump from one pole to the other and the ground simultaneously?

I would tend to disagree with that hypothesis, but I bet we could test this one out easy enough.

 

[JaredJames]

Are you saying that when this arc occurred, it would jump from one pole to the other and the ground simultaneously?

I would tend to disagree with that hypothesis, but I bet we could test this one out easy enough.

I don't believe he said that.

The arc would go either from pole A to pole B or from pole A to the ground (assuming pole A is the one the charge built on).

 

[Naty1]

Let's take our suspended generator and crank it up to a million volts instead of just a wimpy 120 volts. Would that arc jump from one pole of the generator to the Earth or would it jump from one pole of that generator to the other?

In general, it will arc along the shortest air path...The voltage in a spark plug, for example, can arc the 1/16" or so of separation between the electrodes...won't go six feet, for example...

When the air ionizes, electrical current beginns to flow...you'll possibley smell ozone, a product of the ionization...I think it's pretty much the same as cornoa breakdown:


http://en.wikipedia.org/wiki/Electrical_breakdown#Corona_breakdown

Partial breakdown of the air occurs as a corona discharge on high voltage conductors at points with the highest electrical stress. As the dielectric strength of the material surrounding the conductor determines the maximum strength of the electric field the surrounding material can tolerate before becoming conductive, conductors that consist of sharp points, or balls with small radii, are more prone to causing dielectric breakdown. Corona is sometimes seen as a bluish glow around high voltage wires and heard as a sizzling sound along high voltage power lines.

The boldface is mine and supports my prior post...

 

[Studiot]

I think Brer Rabbit is trying to play the same game here he plays with Brer Fox and Brer Bear,

Trying to convince them black is white.

 

[Evil Bunny]

I don't believe he said that.

The arc would go either from pole A to pole B or from pole A to the ground (assuming pole A is the one the charge built on).

He's not saying much of anything. Which is why I'm trying to get an explanation. I posed a question. Would the arc jump from pole to pole or pole to ground? He said both. I'm trying to guess what he means because he hasn't told us. He was very quick to bring lightning into the conversation as proof of... something? I'm just trying to get to the bottom of why the arc from pole A (for example) would only want to jump to pole B and not to the ground like lightning does. I honestly don't know the answer. Maybe this explanation will help clear things up for me.

I think Brer Rabbit is trying to play the same game here he plays with Brer Fox and Brer Bear,

Trying to convince them black is white.

I'm not trying to convince anyone of anything. I am only trying to get a better understanding of how electricity (whatever that means) works...

 

[JaredJames]

Where did anyone say it would jump to both simultaneously?

The arc will jump through the path of least resistance - this will either be to the other pole or to the ground. There's no more to it than that.

 

[Evil Bunny]

Let's take our suspended generator and crank it up to a million volts instead of just a wimpy 120 volts. Would that arc jump from one pole of the generator to the Earth or would it jump from one pole of that generator to the other?

In general, it will arc along the shortest air path...

Let's put them the exact same distance apart. Pole B and the Earth are now the exact same distance from Pole A. We start increasing the voltage until an arc occurs. The arc originates from Pole A... where does it go?

I say it goes to Pole B even if it was farther away than earth. The "desire" to go to the Earth is not there. Correct?

Lightning... on the other hand...

 

[JaredJames]

Let's put them the exact same distance apart. Pole B and the Earth are now the exact same distance from Pole A. We start increasing the voltage until an arc occurs. The arc originates from Pole A... where does it go?

I say it goes to Pole B even if it was farther away than earth. The "desire" to go to the Earth is not there. Correct?

No. There is absolutely no desire.

As per my previous post, it follows the path of least resistance. (This of course, assumes the ground and pole b are equal in charge.)

 

[Evil Bunny]

Where did anyone say it would jump to both simultaneously?

Post #25 except for the "simultaneously" part. Would one happen first? Again... little explanation. Hard to tell.

The arc will jump through the path of least resistance - this will either be to the other pole or to the ground. There's no more to it than that.

But there is. Didn't we say that there wasn't even a voltage present between the ground and the pole? Why would it ever want to go to the ground in the first place?

 

[JaredJames]

Post #25 except for the "simultaneously" part. Would one happen first? Again... little explanation. Hard to tell.

He said both were likely to happen, not that both would. There is a difference.

But there is. Didn't we say that there wasn't even a voltage present between the ground and the pole? Why would it ever want to go to the ground in the first place?

There is always a potential difference between two points. It's just a matter of how much of a difference.

If the pole is at 1 million volts and the ground is zero (as per your previous post) then there is a potential difference between the ground and the pole.

You may want to go back and learn the basics of electricity.

 

[Evil Bunny]

If the pole is at 1 million volts and the ground is zero (as per your previous post) then there is a potential difference between the ground and the pole.

The million volts was between the two poles. 0 volts between pole and ground, remember...

 

[JaredJames]

The million volts was between the two poles. 0 volts between pole and ground, remember...

If your pole is at 1 million volts and the ground is at zero, there is a potential difference between them.

Think of an electric line power line. The line is at 400,000V and the ground is your zero reference. The only reason it doesn't arc is because the path of least resistance is to follow the wire.

Now, if I get close enough to the wire, suddenly the path of least resistance is to arc through the air, through me and into the ground. And so it changes direction and follows that route instead - until I move away.

 

[Evil Bunny]

The utility company ties one of their two poles to the ground. That is the only reason there is a potential there. We did not do that. That is a very critical point to this thread. Go back and read carefully.

 

[JaredJames]

The utility company ties one of their two poles to the ground. That is the only reason there is a potential there. We did not do that. That is a very critical point to this thread. Go back and read carefully.

What you have posted is the inversion of one of the standard procedures for servicing of HV lines.

They use a helicopter to allow someone to work on the lines whilst live. As the helicopter is not grounded, there is no potential (or very little) potential between it and the lines - so no arc.

In this case, it won't arc to the ground but to the other pole. EDIT: Assuming path of least resistance is to the other pole.

However, with a significant charge imbalance you will get an arc between the pole and the ground - as with static (lightning).

 

[Evil Bunny]

In this case, it won't arc to the ground but to the other pole.

However, with a significant charge imbalance you will get an arc between the pole and the ground - as with static (lightning).

Perfect... Ok so my main reason for posting this is because I am having a hard time understanding why we can develop a large potential (between the two poles of my imaginary hovering generator) and not have the electrons make their way from the Earth to one of these poles. I would think that these electrons in the Earth would be attracted to one of these poles because of a huge difference in charge, but this is apparently not the case.

Why?

I think the explanation was given by Naty1 in post # 12 of this thread but I'm still having a hard time grasping the concept.

Lightning was also brought into this conversation and rightly so... Obviously there are scenarios where the potential between cloud and ground becomes so great that we ionize the air and lightning occurs. What is the difference? Is it sheer magnitude of voltage? Are we simply not generating enough voltage to "encourage" interaction between the generator pole and ground? Or does voltage (between the two generator poles) have absolutely nothing to do with this "charge" that causes lightning?

 

[JaredJames]

Lightning was also brought into this conversation and rightly so... Obviously there are scenarios where the potential between cloud and ground becomes so great that we ionize the air and lightning occurs. What is the difference? Is it sheer magnitude of voltage? Are we simply not generating enough voltage to "encourage" interaction between the generator pole and ground? Or does voltage (between the two generator poles) have absolutely nothing to do with this "charge" that causes lightning?

It's worth pointing out, if you moved the generator so that the path to Earth had less resistance than to the other pole, it would arc to the earth. This is like static electricity from a car.
The car becomes charged due to sunlight on a hot day. It is not grounded to the earth, but when you touch it you ground it and so receive the shock.
This is true for electrical lines as well, regardless of whether or not they are in grounded at some point. The reason it arcs is not because the company ground the cables at some point.

In the case of lightning, it is only when the charge builds up enough to give you a large enough driving voltage to arc to the ground. So yes, it's all about voltage.

 

[rcgldr]

The utility company ties one of their two poles to the ground.

In the USA, at most (but not all) transformers, the center tap of the transformer is is grounded, so that at the final step down transformer, and at a household, the neutral ends up +/- 10 volts of Earth ground. At my house, it's close, about .3 to .5 volts, but it's not zero. The final step down transformer only has 2 lines going into it, 6900 volts ac, and steps the voltage down to 220 volts, with a non-grounded center tap to provide a neutral. At my house hold, there is a grounded rod used for the third round pin socket on 3 pin plug sockets. The wide pin socket hole is neutral, and the narrow pin socket plug hole is one of the two end taps from the transformer, to provide 110 volts. A 220 volt socket would use both ends of the transformer, plus the grounded line.

They use a helicopter to allow someone to work on the lines whilst live. As the helicopter is not grounded, there is no potential (or very little) potential between it and the lines - so no arc.

There's a huge potential beteen helicopter and the line. The first part of the procedure is to extend a probe connected to the helicopter and the line being worked on, so that both helicopter and the line end up at the same potential, You often see significant arcing during the connection process. The line is then connected to the helicopter while the worker moves onto the line, then the line is disconnected. This processis repeated again when the worker leaves the line. The worker also uses a faraday cage like suit so any current flow or transformer effects of working on a single wire go thorugh the suit and not the worker. Example video:



There are also line inspector robots a bit less than 1 meter long that rely on a transformer effect from the two points on a single line to power them so they can move on high power, high tension lines. (I couldn't find a video of these in action). Just the field from these lines is strong enough to light up flourescent bulbs:

http://www.stopgeek.com/richard-boxs-light-field.html

 

[JaredJames]

There's a huge potential beteen helicopter and the line.

Initially yes, I meant later with the guy jumping about. The fact the helicopter never gets to the point of creating the path of least resistance means they can get to a zero potential level. So no arc when he's messing about.

It's what I was trying to clarify with my last post regarding moving closer to the earth.

 

[Evil Bunny]

It's worth pointing out, if you moved the generator so that the path to Earth had less resistance than to the other pole, it would arc to the earth.

No it wouldn't. It's all about where these electrons want to go. They don't want to go to the earth, they want to go to the other pole. We talked about it in this very thread. If you put a straight wire from pole A to earth, virtually no current would flow (the same is true between pole B and the earth). If you put a straight wire from pole A to pole B the wire would quickly melt from all the current.

This is like static electricity from a car.

No, it's not actually... And this is what I'm trying to find out. What is different about it? This "static" electricity that shocks you when you touch your door knob or your car or allows you to stick a balloon to the wall is the same as lightning.

But it's not the same as having a voltage potential between these two wires of the "source" (generator) and their relationship to the earth.

This is the whole point of the thread. I'm looking for an explanation of what is different about it.

I guess I'm just not explaining it very well. I'm probably not asking it the right way or something.

 

[Evil Bunny]

In the USA, at most (but not all) transformers, the center tap of the transformer is is grounded, so that at the final step down transformer, and at a household, the neutral ends up +/- 10 volts of Earth ground. At my house, it's close, about .3 to .5 volts, but it's not zero. The final step down transformer only has 2 lines going into it, 6900 volts ac, and steps the voltage down to 220 volts, with a non-grounded center tap to provide a neutral. At my house hold, there is a grounded rod used for the third round pin socket on 3 pin plug sockets. The wide pin socket hole is neutral, and the narrow pin socket plug hole is one of the two end taps from the transformer, to provide 110 volts. A 220 volt socket would use both ends of the transformer, plus the grounded line.

The primary of the transformer has one side attached to HV (6900VAC in your example) and the other side attached to the "return" which is the wire located underneath the HV line parallel with it on your utility pole). The "return" side of the primary is also attached to ground by a large conductor and a rod driven into the earth... The secondary has two "hots" and one center tapped neutral coming out of it. The center tapped neutral absolutely is grounded. It is grounded with the same conductor that is grounding the primary of the transformer. The two "hots" give you 240 Volts between them. Either of the "hots" give you 120V when referenced to the center-tapped neutral.

The bare copper wire (third round pin) is used for "bonding" metal parts in your structure together and they are also tied into the "neutral" as well as the "ground rod" at your service entrance.

 

[JaredJames]

The primary of the transformer has one side attached to HV (6900VAC in your example) and the other side attached to the "return" which is the wire located underneath the HV line parallel with it on your utility pole). The "return" side of the primary is also attached to ground by a large conductor and a rod driven into the earth... The secondary has two "hots" and one center tapped neutral coming out of it. The center tapped neutral absolutely is grounded. It is grounded with the same conductor that is grounding the primary of the transformer. The two "hots" give you 240 Volts between them. Either of the "hots" give you 120V when referenced to the center-tapped neutral.

The bare copper wire (third round pin) is used for "bonding" metal parts in your structure together and they are also tied into the "neutral" as well as the "ground rod" at your service entrance.

I'm curious how you can know all this without knowing the reasons (physics) behind it - or at least some knowledge.

 

[JaredJames]

No it wouldn't.

No, it's not actually...

Right, you need to check a few things here. I suggest you read up what charge is and what voltage is before we continue.

As rcgdlr said, you get an arc between the helicopter and the power lines - note that the helicopter isn't grounded.

Initially, the PD between the two is so high, you get the arc - much like static shocks.

 

[Evil Bunny]

I'm curious how you can know all this without knowing the reasons (physics) behind it - or at least some knowledge.

The reason for grounding the distribution system in the United States is put forth in the NEC. They mention things like stabilizing voltages and protection against line surges and lightning strikes and unintended contact with high voltage sources... the article is 250.4 (A)(1) I think but I don't have it in front of me.

I definitely have some knowledge, but I'm looking for more. I don't understand how we can have a potential voltage on a pair of wires (like our generator scenario) and not have a potential between either one of those wires and the earth. It just seems like there would be some "charge" on the wire that would want to interact with the electrons in the earth.

My brain hurts... I need to take a break from this and regroup.

 

[rcgldr]

The bare copper wire (third round pin) is used for "bonding" metal parts in your structure together and they are also tied into the "neutral" as well as the "ground rod" at your service entrance.

Then why do I see .3 to .5 volts between ground and neutral at my house? I've asked a few of my friends to do measure the difference at their houses, and the voltage is a bit under 1 volt, but it's never zero. I've seen the final transformer (it's less than 100 feet from my house) when it was being serviced. Two well insulated lines going in, 3 well insulated lines going out (the two hots and neutral), none of them are grounded.

 

[Studiot]

Since my meaning was still in dispute:

Friction causes some clouds to become charged with static electricity. Some become positive, some become negative so act like battery poles.

If you watch the heavens you can see some lightning flashes between one cloud and another.

You can also see lightning flashes between some clouds and ground.

Both types of flash act to discharge the clouds and we all know just how energetic and destructive a lightning flash can be.

I am only trying to get a better understanding of how electricity (whatever that means) works...

Then I (respectfully) suggest you prick up those long bunny ears and do more listening and less expounding.