Isolation transformer and electrons

[IanB]

If I reference to this picture. Because earth has everywhere potential of 0 V, how do electrons find the correct path through earth to the transformer? If we have a town with 20 transformers, and we create a short circuit somewhere on the grid, how do electrons know where to flow to that one transformer of the total 20?

Maybe a better answer:

If the electrical distribution transformers are connected to ground at the point of supply (as they normally are), then if you make another connection to ground somewhere else on the network (your short circuit), then there is a potential gradient through the ground between the two connection points. Current will flow in the direction of decreasing potential through the ground, which will take it back to the source.

This is like the direction of current flow in a lake. If there is an outfall at the edge of the lake then water will flow towards the outfall to maintain a level surface. You cannot see the potential gradient that causes the water to flow across the lake, but it is there.

[Shock]

If I reference to this picture. Because earth has everywhere potential of 0 V, how do electrons find the correct path through earth to the transformer?

Firstly the analogy was just to give you an idea how current flows in a circuit. Don't read into it too much. I'd also get away from this earth is 0V idea, it's just earth a circuit path (not a great one either).

Not sure I understand your question, but if you are referring to mains distribution, it works like any other circuit, the least path of resistance will be taken as the return path. Which is going to be the neutral line over some ground/earthing rod in soil.

The earthing of the neutral throughout distribution systems from what I read a while back was to prevent dangerous DC voltages on the AC lines from lighting strikes and then added to homes then as a separate path to appliances.

If we have a town with 20 transformers, and we create a short circuit somewhere on the grid, how do electrons know where to flow to that one transformer of the total 20?

Not sure I understand your question. If the one transformer had a completed secondary circuit allowing more current to flow it would cause the magnetic field (magnetic flux density) to increase which increases current flow on the primary.

There are ideal components and real components, if the transformers primary is connected it's actually using a small amount of current even if the secondary is open. So the first part of the answer is that current is already flowing.

When you have two conductors that have a voltage potential across them it does not need to find a pathway from the electrical station/substation/transformer/battery etc, it already has one and is sitting there waiting for the circuit to be completed. The magic happens straight away.

[ArthurDent]

nforce – “If I reference to this picture. Because earth has everywhere potential of 0 V, how do electrons find the correct path through earth to the transformer? If we have a town with 20 transformers, and we create a short circuit somewhere on the grid, how do electrons know where to flow to that one transformer of the total 20?”

Once again, the language of science is math, not feelings, and electrons don’t willy-nilly choose to do or not do something, they follow the laws of science. First you have to understand how grounding works in a power distribution system. There are countless utility poles and many of them have grounding rods driven into the physical ground for system safety but in a single phase residential distribution system besides the hot line there is always a neutral wire that is connected to these ground rods at many poles and connected to neutral throughout the entire system without relying on ground except for safety. Here is a drawing showing how in a single MV (medium voltage-maybe 2500V) feeder circuit is grounded. Every so often there is a step-down transformer that has a 240V center-tapped winding and the center tap is also connected to ground, both at the pole and in any house it’s connected to.

The distribution system is the 2 feeder wires (hot and low) with as many loads (transformers) connected as needed up to the power rating of the distribution line. If there is a short at any transformer secondary, it has a primary fuse that will blow so it won’t take the entire distribution line down but all the houses fed from the transformer output will lose power.

If there is a short on the 2500V distribution line causing the distribution line fuse to blow at the sub-station then all the houses connected to all the transformers on that entire distribution line will lose power.

If there is a short on the sub-station feeding the distribution lines going to neighborhoods then all the houses connected to all the distribution lines connected to the power sub-station will lose power and earth ground could care less. 

[nForce]

Hmm, but I want to know from electrons perspective. Maybe IanB gave a better answer.

So if I understand correctly: When we make a short circuit on the grid, those electrons flow from a transformer through wire into ground. Now the transformer has electron "holes" and the earth (our planet) has negative charge. Because of that the transformer tap, which is grounded suck electrons from the ground, to fill the "holes". Now everything is again balanced the earth and the transformer. Altough our planet is very large, so excess of electrons would be negligible.

Sorry but my question is pure physics, and not engineering.

[Shock]

This is where the electrons are going in a completed AC circuit.

[ArthurDent]

nForce - "So if I understand correctly: When we make a short circuit on the grid, those electrons flow from a transformer through wire into ground. "

No, no, no! Read what I posted. The ground (earth) is only a safety connection that the zero volt reference wire (neutral) is connected to at many points along the distribution route. If all the wires from the poles to the ground were removed the system would still function because, as I said:

there is always a neutral wire that is connected to these ground rods at many poles and connected to neutral throughout the entire system without relying on ground except for safety.

The electrons have no perspective, they could care less, but they are absolutely law abiding and follow ohms law to the letter.

[nForce]

nForce - "So if I understand correctly: When we make a short circuit on the grid, those electrons flow from a transformer through wire into ground. "

No, no, no! Read what I posted. The ground (earth) is only a safety connection that the zero volt reference wire (neutral) is connected to at many points along the distribution route. If all the wires from the poles to the ground were removed the system would still function because, as I said:

there is always a neutral wire that is connected to these ground rods at many poles and connected to neutral throughout the entire system without relying on ground except for safety.

The electrons have no perspective, they could care less, but they are absolutely law abiding and follow ohms law to the letter.

I meant ground, as an earth. We are standing on the earth and touch the hot wire.

[nForce]

This is where the electrons are going in a completed AC circuit.

Yes, so the electrons are switching between earth and the wire, and between earth and the transformer. But my point was about the earth (planet).

[001]

google Kirhgoff law

[IanB]

I meant ground, as an earth. We are standing on the earth and touch the hot wire.

It's still not clear that you understand.

Get a loose piece of wire and wave it around in the air. What is the voltage of the wire? Answer: it has no voltage. It is not 0 V, it is not zero, it is simply undefined. We do not know what the voltage is. If you touch it, no current will flow because there is no voltage.

Now imagine the Earth as a big ball of wire floating in space. What is the voltage of the Earth? Again, we do not know. It is undefined. If you stand on the Earth no current will flow. The Earth is isolated because space is an insulator.

So now, consider a transformer. It will have two wires coming out of it. Neither wire has any voltage relative to ground because the winding is isolated. Neither wire is hot, and neither wire is neutral. If you touch either wire while standing on the ground nothing will happen.

Next, suppose we connect one wire to a rod in the ground. We have now made this wire neutral, and the other wire has been made hot. It wasn't hot before, but now it is.

So now, what happens if we touch the hot wire? Now there is a circuit made and current can flow. The current flows through you, through the Earth (a big ball of wire), through the rod in the ground, and back to the transformer.

When you say "short circuit" you need to understand that "circuit" means a closed loop, out and back again. So a "short" circuit is a shorter loop than the one intended. That's it.

[Gregg]

The following is an attempt to provide the OP with another viewpoint toward understanding the question posted; it may not be 100% correct due to simplification. 

nForce,
It may help to let go of thinking of electrons actually flowing like so many basic explanations comparing electricity to water suggest.  It may be closer to reality to consider the electrons more like the balls of a Newton’s cradle where a force on one end of the set causes an almost equal reaction on the far end.  Electrons are not free to flow like water in a hose; a good conductor just has the electrons not as tightly attracted to the nucleus as an insulator.  From the electron’s perspective, it gets kicked from one nucleus to the next and thereby kicking another electron on down the line.  If the potential continues or reverses, it may be a different electron that gets kicked away, but none of them go very far of and by themselves.   
If a force is applied to an isolated wire to cause electrical potentials like shown in the graphic posted by Shock with neither end connected to make a circuit, the electrons don’t jump off the ends of the wire; the wire in this instance acts like a capacitor, the charge potential varies from end to end but there is no circuit.  The graphic probably would be closer to reality if it showed the blue dots being packed tighter at one end and farther apart at the other rather than disappearing from the ends.
To get back to the transformer: the secondary is an isolated wire with potential(s) being induced by the magnetic fields created by the primary.  Even if the primary has a connection somewhere in its circuit connected to ground, from the perspective of the electrons in the secondary they are like stars in the night sky; they may have potential energy but no measurable interaction.  To put the transformer question into a very basic scenario: take two batteries (your choice) and connect a terminal of one to the earth ground; try measuring any potential to ground from the second battery and because there is no circuit there is no potential from either terminal of the second battery to ground even though each battery has its own potential.
In other words potential is just potential, nothing happens unless there is a circuit.  Most electrical parameters need to be considered as circuits first and what is happening in the circuit all the way from the source back to the source.  The secondary of a transformer is considered to be an isolated source.  Potential is how far you need to keep your fingers away.  Amperage is the damage it can do if the circuit resistance or impedance is lower than needed to keep it under control. 
Old school AC welding machines are an example of transformers similar to the posted question.  These  devices were merely a transformer with a few taps on the primary that stepped the voltage (potential) down to a level less than lethal while stepping the amperage (ability to melt metal welding rods and add heat to the substrate) up with a core that easily saturated before drawing more current than the input could provide. One arbitrary output terminal was connected to the metal being welded, usually considered “earth”.  Several of these welders could be connected to the same potential steel via the building structure, ship hull etc. but the different welders wouldn’t swap electrons and interact because they were different circuits and the potential only existed for each individual circuit.  More modern welding machines are usually SMPS DC but the output still has to be isolated.
Then there are autotransformers.  Transformers with isolated secondaries can be used as autotransformers such that the secondary potential can be either added or subtracted from the primary; however caution needs to be exercised as to the connections.  Then there are autotransformers that have only one winding a configuration most Variacs utilize.  Look it up for further details.

[Shock]

Yes, so the electrons are switching between earth and the wire, and between earth and the transformer. But my point was about the earth (planet).

The earth as a whole is considered neutral. It has the ability to conduct (and alternate) electricity in a completed circuit. Though not the most reliable conductor of electricity which is why ground/earth rods are sunk into favorable conditions depending on the soil type, moisture, depth.

There is actually a high voltage transmission line system called "Single Wire Earth Return" which just uses one conductor and the earth to complete the circuit over long distances.

As mentioned, the Neutral side of the mains is connected to Earth throughout the distribution network at various points (at least here it is). Because the mains is now Earth referenced (not floating) making a connection between Live and Earth to complete a circuit will cause electrons to move back and forth like I showed in the previous image.

How far do the individual electrons travel in a Live to Earth circuit? Not very far at all, they would alternate similar as with wires given the same propensity to conduct. Do they still alternate in the ground, earth, soil? Yes where it's conducting and not 100% insulating.

What path do they take to complete the circuit? The majority would be "shared paths" of least resistance to the nearest neutral line I would imagine. Perhaps there is also some capacitive effect as well, I'm not sure. But we know electrons alternate through conductors, even poor ones. They tell us this at school .

[SG-1]

nForce, I think you would find the electricity articles here very interesting:

http://amasci.com/elect/elefaq.html

[wbeaty]

It may help to let go of thinking of electrons actually flowing like so many basic explanations comparing electricity to water suggest.  It may be closer to reality to consider the electrons more like the balls of a Newton’s cradle where a force on one end of the set causes an almost equal reaction on the far end. 

OK, but electrons also flow too.  An electric circuit is like a flywheel made of electrons, where if you push on one part, the whole thing turns as a unit.  (So, it's like a circular Newton's cradle!  Or like a loop of hose that's completely full of metal spheres, all lined up.  Jerk one sphere, and fast waves fly all around the loop, but also, all the spheres move ahead, like a turning wheel.)

Electrons are not free to flow like water in a hose; a good conductor just has the electrons not as tightly attracted to the nucleus as an insulator. 

Not true.  Electrons in metals are free to flow, very much like water in a hose.  They flow slowly as a group, while the waves (the energy) zoom fast.  The "flywheel" turns slowly, but the whole thing turns as one, so energy can flow almost instantly to every part of the "wheel."   

In a good conductor, the electrons have left their original atoms, and are orbiting around all through the metal.  In other words, they're jumping between atoms all the time, inside all metals everywhere.  This is more like a vibration than like a flow.   An "electric current" is when they jump slightly more in one direction.  They all move along in one direction, while also jumping/vibrating.  (Air and wind is similar, where individual air molecules are always wiggling, even when the "air" is still, with zero wind.  The energy in wires is like sound waves.  The electric current is like slow wind.) 

But inside an insulator, the electrons don't do this, but instead stay in their individual atoms.    If metals are full of "electron liquid," then insulators are choked with solid "electron ice."

[wbeaty]

But how do electrons know on the other side of an isolation transformer that we don't have a current loop?

Simple:  in circiutry, electrons flow in loops only.   

But don't just accept this answer; instead ask why.

Why do electrons only flow in loops?   It's because if we wanted them to flow in a one-way direction, we'd need kilovolts, megavolts, to apply enough force.   Electrons are actively held inside of wires by their enormous attraction to the positive charges of atom nuclei.  The electrons of the metal can flow in a loop, but can't leave the metal circuit.

If electrons in a circuit are like a flywheel, then it's very easy to spin the flywheel, but very hard to pull chunks out of it.    That's why electrons stay inside the isolated circuit: an immense voltage-force would be needed if you wanted to push any of them out of the loop and into the Earth.   

Why?  It's because metals are half electrons, half protons, all in balance and strongly attracting.  If we make electrons flow in a circle, then they always stay near some protons.  But if we try to make them flow in one direction, then we're fighting against an immense-but-unnoticed attraction-force.  We're pulling them away from the enormous positive charge inside the copper.

---

Also, always remain aware that one wire doesn't "have a voltage."

Instead, each wire has many voltages at the same time (voltage WRT the ground is usually kilovolts, voltage WRT the sky is megavolts, WRT the sun or moon is even higher.)     In other words, voltage is like altitude, and your body doesn't "have altitude."  The altitude of a single point is meaningless.   Altitude is always measured between two points.  So, your body has many altitudes at the same time: altitude above the floor, altitude above the dirt, altitude above the average local landscape, altitude above sea-level, altitude above the center of the earth...  and voltage behaves like that.

The Earth isn't actually at zero volts.   Instead, we'll find several megavolts between Earth and sky (ionosphere.)    We could say that the sky is at +1.5MV and the Earth is at -1.5MV.   Or say that the sky is at zero volts and the Earth is at -3MV.  Both are true at the same time, because Earth's surface has many voltages all at the same time  ...because voltage is always measured between two points.   

The word "electric potential" means something like length-in-an-E-field.    And length only has meaning when it's measured between two points.

[Zero999]

Hmm, but I want to know from electrons perspective. Maybe IanB gave a better answer.

So if I understand correctly: When we make a short circuit on the grid, those electrons flow from a transformer through wire into ground. Now the transformer has electron "holes" and the earth (our planet) has negative charge. Because of that the transformer tap, which is grounded suck electrons from the ground, to fill the "holes". Now everything is again balanced the earth and the transformer. Altough our planet is very large, so excess of electrons would be negligible.

Sorry but my question is pure physics, and not engineering.

In the distribution transformer scenario, the earth simply acts as a return conductor for the current path. If one side of the transformer isn't connected to earth, then there will be no return current path, so no current will flow, as is the case with the isolation transformer, when the other side isn't earthed.

[Brumby]

YES!  I've been wanting to express something like this - but haven't had the time to put the words together.  Thanks to wbeaty!!

I would make one change, which I have highlighted...

Why do electrons only flow in loops?   It's because if we wanted them to flow in a one-way direction, we'd need kilovolts, megavolts, to apply enough force.

eg Lightning.

Electrons are actively held inside of wires by their enormous attraction to the positive charges of atom nuclei.  The electrons of the metal can flow in a loop, but can't leave the metal circuit.

If electrons in a circuit are like a flywheel, then it's very easy to spin the flywheel, but very hard to pull chunks out of it.    That's why electrons stay inside the isolated circuit: an immense voltage-force would be needed if you wanted to push any of them out of the loop and into the Earth.   

Why?  It's because metals are half electrons, half protons, all in balance and strongly attracting.  If we make electrons flow in a circle, then they always stay near some protons.  But if we try to make them flow in one direction from point A to point B and not in a loop, then we're fighting against an immense-but-unnoticed attraction-force.  We're pulling them away from the enormous positive charge inside the copper.

[Brumby]

The first thing you need to do is set aside electrostatic examples such as lightning.  That deals with single discharge events on not a continuous current flow.

The other thing you need to understand - and there has been a LOT of effort in this thread to try and make this point - is that there is no such thing as an absolute voltage.  It is ALWAYS a voltage at one point with respect to another point.  Whether you realise this or not, you prove this point every time you make a voltage measurement.  If you connect one probe from your multimeter to a voltage source (say a 9V battery) and don't connect the other probe, then you aren't going to get a voltage reading.

Further, if these two points are not electrically connected in some way, then you cannot measure the voltage between them - because there is no difference in their potential.  To prove this, connect one probe from your multimeter to the positive terminal of one 9V battery and connect the other probe to the negative of a second 9V battery - with no connection between the batteries.  Again, you aren't going to get a meaningful voltage reading.

However, once you make a connection between these two batteries, you have defined voltage relationships and you will get a voltage reading that is meaningful.  Note that if you make exactly one connection between the two batteries, you will not create any short circuits, but depending on which of the four possible connections you could make (with the probes connected as above), then you will get a voltage reading of 0V, +9V or +18V.  Swap the multimeter probes and the sign of the voltages will change.

In all these cases, the multimeter completes a circuit when meaningful measurements are given.


The primary and the secondary of a standard transformer are two separate electrical circuits.  The fact that they are coupled magnetically has NO impact on their behaviour as separate electrical circuits (other than the transformer action).

[IanMacdonald]

Interesting point is that an electric current is rather like a hydraulic circuit, in that the 'fluid' (electrons) doesn't have to go through the whole length of the pipe (cable) to do work. Electrons going in one end, jostle the rest along, so some come out the other end. Not the same ones that went in, though. In fact, the to-and-fro movement of the electrons in a 50Hz AC circuit is quite short. So it's more like a vibration than a flow.

https://en.wikipedia.org/wiki/Drift_velocity#Numerical_example

[ArthurDent]

Hero999 – “In the distribution transformer scenario, the earth simply acts as a return conductor for the current path. If one side of the transformer isn't connected to earth, then there will be no return current path, so no current will flow, as is the case with the isolation transformer, when the other side isn't earthed.”

That is absolute incorrect. If you had read my post #27 and post #30 you would know that the earth grounding of the neutral wire (that is the actual return conductor for the current path) is a safety feature and the earth isn’t relied on for carrying current.

The reason for this is simple, the earth’s resitivity is a variable that varies wildly from fairly low in some areas to near infinity in rocky areas. Power distribution has to be known and controlled and utilities can’t have one customer’s lights dim or flickering while the neighbor’s lights are very bright. Two wires are used and ground is only a safety connection.

This confusion is possibly caused by the misunderstanding of what the proper definition of ‘ground’ is. Here is a good description to help clear the confusion many have and is titled “An Introduction to Ground: Earth Ground, Common Ground, Analog Ground, and Digital Ground”.
https://www.allaboutcircuits.com/technical-articles/an-introduction-to-ground/

More specifically, in the case of power distribution being discussed, here is a document that describes a power distribution system and the ground connections used for safety.
http://www.samlexamerica.com/support/documents/13007-0612_GroundedElectricalPowerDistribution.pdf

1.0 CONDUCTORS FOR ELECTRICAL POWER DISTRIBUTION
For single-phase transmission of AC power or DC power, two conductors are required that will be carrying the current. These are called the “current-carrying” conductors. A third conductor is used for grounding to prevent the build up of voltages that may result in undue hazards to the connected equipment or persons. This is called the “non current-carrying” conductor (will carry current only under ground fault conditions).
2.0 GROUNDING TERMINOLOGY
In electronics, Ground is considered to be a common point, a point of zero potential and an infinite sink of electrons. In reality, most points we consider “grounded” are far from this perfect state. For purposes of electrical power transmission and distribution, the term “Grounded” indicates that one or more parts of the electrical system are connected to Earth, which is considered to have zero voltage or potential. In some areas, the term “earthing” is used instead of grounding. Connection to Earth may be made using Earth Electrodes like ground rods, buried wires, metallic pipes and other conductors in contact with the Earth.
Earth Ground is described in the context of lightning protection, safety and operational performance and is used for the following functions:
• Dissipate lightning strike energy in a manner that protects the surrounding area. Please see details under the Section 6 titled “Grounding System and Lightning / Ground Fault Protection”
• Provide a low impedance connection back to the AC power mains Ground or Neutral to reliably clear fault conditions by blowing a fuse or by tripping a circuit breaker. A “fault condition” occurs when a live, ungrounded current carrying conductor comes in contact with the exposed metal parts of electrical equipment
• Reduce the step potential gradient to safe levels
• Form a natural sink for atmospheric and radiated noise
• Provide an electrical antenna counterpoise.

[nForce]

Yes, so the electrons are switching between earth and the wire, and between earth and the transformer. But my point was about the earth (planet).

The earth as a whole is considered neutral. It has the ability to conduct (and alternate) electricity in a completed circuit. Though not the most reliable conductor of electricity which is why ground/earth rods are sunk into favorable conditions depending on the soil type, moisture, depth.

There is actually a high voltage transmission line system called "Single Wire Earth Return" which just uses one conductor and the earth to complete the circuit over long distances.

As mentioned, the Neutral side of the mains is connected to Earth throughout the distribution network at various points (at least here it is). Because the mains is now Earth referenced (not floating) making a connection between Live and Earth to complete a circuit will cause electrons to move back and forth like I showed in the previous image.

How far do the individual electrons travel in a Live to Earth circuit? Not very far at all, they would alternate similar as with wires given the same propensity to conduct. Do they still alternate in the ground, earth, soil? Yes where it's conducting and not 100% insulating.

What path do they take to complete the circuit? The majority would be "shared paths" of least resistance to the nearest neutral line I would imagine. Perhaps there is also some capacitive effect as well, I'm not sure. But we know electrons alternate through conductors, even poor ones. They tell us this at school .

So electrons also alternate in the earth, when conducting in the loop?

[Zero999]

Hero999 – “In the distribution transformer scenario, the earth simply acts as a return conductor for the current path. If one side of the transformer isn't connected to earth, then there will be no return current path, so no current will flow, as is the case with the isolation transformer, when the other side isn't earthed.”

That is absolute incorrect. If you had read my post #27 and post #30 you would know that the earth grounding of the neutral wire (that is the actual return conductor for the current path) is a safety feature and the earth isn’t relied on for carrying current.

The reason for this is simple, the earth’s resitivity is a variable that varies wildly from fairly low in some areas to near infinity in rocky areas. Power distribution has to be known and controlled and utilities can’t have one customer’s lights dim or flickering while the neighbor’s lights are very bright. Two wires are used and ground is only a safety connection.

I'm aware of that. I did read your posts, but they refer to distribution transformer, rather than the original poster's set-up. The original poster is also in Europe and you refer to a US distribution system which is very different.

Yes, the earth can act as a current return path. In most installations, the neutral conductor should only be intentionally used as a return current path, but the earth is a common return path, under fault conditions.

Note that in some installations, the earth is indeed the sole path for the return current.
https://en.wikipedia.org/wiki/Single-wire_earth_return

What I was attempting to explain was that in the case of an isolation transformer, the secondary is not connected to earth, therefore there is no return path for the current, via earth. If a meter were connected from anywhere on the secondary to earth, it will ideally read 0V. In the case of a distribution transformer, the secondary is connected to earth, so connecting a meter between the live and earth would result in the full supply voltage being read.

[ArthurDent]

Post #40 Hero999 – “In the distribution transformer scenario, the earth simply acts as a return conductor for the current path.”
Post #46 Hero999 – “I did read your posts, but they refer to distribution transformer, rather than the original poster's set-up.
As in your post #40 I am indeed talking about the distribution transformer scenario, as you were.

Hero999 – “The original poster is also in Europe and you refer to a US distribution system which is very different.”
Whether it’s the U.S. or Antarctica they still use wires to make a circuit. They do not rely on ground for a return path, only for safety. Back in the 1800s for telegraph (low current, low voltage) they had used it but switched. Rarely, in extremely high voltage long distance transmission, ground has been used as a return where the resistance of the ground and the current used is relatively small compared to the voltage. It has been tried and kind of works in these special applications. What was being discussed here was a medium voltage neighborhood distribution system where there is a physical wire used as the return and the ground is just part of the protective or safety circuit, not a return path as you indicated in your drawing. If the ground had any typical resistance at all you would never get full voltage to the load.

Also in your drawing you show a 3-phase system which is mainly used for larger industrial applications and not residential. Even with that, the assumption of ground being the return path is incorrect. Here is how it is described:
“Wye vs. Delta Connections
Starting with Wye, the connection consists of a total of five wires: (3) hot, (1) ground and (1) neutral. The configuration closely resembles a letter Y, with the neutral component connected at the middle, which is also where all the lines converge. It is at this point wherein the voltages are all equal.
It is important to point out that the phase and line current are also considered to be equal. Multiplying the phase voltage by 1.732 (or square root of 3) will result in arriving at the voltage present between any of the two lines. In a Wye system, 120V can be measured from any hot wire to neutral. Additionally, 208V is measured from hot wire to hot wire. This is also the same for Delta configurations.
By comparison, a Delta circuit inside a transformer appears as a triangle with equal sides, resulting in a closed path. In most cases, such wiring configurations do not have a neutral and is present on the secondary side of the transformer. The three phases are connected at every meeting point on the triangle. Moreover, a Delta system is equipped with four wires: (3) hot and (1) ground.”

Here is an excellent video from ElectroBOOM that cover a lot of the points discussed, both 3-phase and single phase, and makes it clear. I recommend his videos because they also have entertainment value while showing the pitfalls of doing it wrong.
 

As far as an isolation transformer working I see that you agree with my previous diagram from post #20 on that point.

[IanB]

ArthurDent, you seem to have completely missed the flow of the thread and the context in which answers are being provided. It's also a bit silly and condescending for you to be trying to correct someone (Hero999) who obviously would not make the mistake you are implying.

Let's be clear here: the earth acts as a return conductor for the current flowing through a person standing on the ground who touches a hot wire. If the transformer neutral wasn't grounded at one or more points along the way, the earth would not act as a return path to that transformer.

The misconception that seems to arise from the OP, as much as we can try to understand it, as that somehow the earth/ground is a magical 0 V sink for all voltages anywhere. This is not true. The ground only acts as a magical 0 V sink in as much as it acts as a return path for current back to a source that has a grounded neutral conductor.

[Shock]

So electrons also alternate in the earth, when conducting in the loop?

So again defining the parameters, if there is AC voltage potential between two points then you're ready for current to flow. By completing the circuit or loop it will conduct and at the electron level they will alternate directions at the frequency of the mains.

Like I said previously (unless you want to dive deep) just consider the earth to be a wire and if it's in circuit (and not isolated) electricity will conduct.