it was explained to me that with the advent of power tools utilized in the workplace(after WWII) deaths were occurring due to 110 volt 2 wire cords and under insulation in the tools. or isolation.as i started out in the machine shop in the 1970's we had an antiquated B&D drill motor that i was "hazed" by. as you pressed on the end of the drill motor to apply ample pressure to drill quickly with it would knock you on your keister. i could only imagine being on the deck of a steel boat or metal roof.
glance at an ac power tools info label and check out the double insulated script.
i watched the 555 chip's arrival and yes i used to ride back and forth to the 7-11 testing the vacuum tubes for my dad when the tv went arye.

 

Have a look at this

Want read more go to here https://en.wikipedia.org/wiki/Single-wire_earth_return

 

When I was about 13 my dad decided to take an old washing machine motor and turn it into a lawn mower. His home made mower had no ground circuit. Whenever I cut the grass - if I were bare foot I could feel a definite tingle through my hands and my feet.

Back in the 80's I was working for a company that made Oil Well Drilling Electronics. One of the projects we were working on was a Porosity tool. It had a special chip that operated at giga hertz range. When the board was tested it tested fine. When it was installed into the module it failed. The question was perplexing to the engineers. It was by accident that one afternoon I happened to have my hand on the module (a very large steel drilling collar) and happened to be touching one of the rivets on a power strip. I noticed a charge. When measured the voltage was about 65 volts. That meant that when the operator put the soldering iron to the board - the iron was properly grounded and so was the module, but the power cord the work station was plugged into had a faulty ground. The grounded soldering iron completed a circuit to ground and was blowing out the chip.

When one source is properly grounded and the end user (soldering iron, work station) are not - things start to go wrong. They had computers and all kinds of monitoring devices hooked up trying to determine the failure mode. Discovery of the live current by accident actually solved the mystery.

Can you get a shock from an improperly grounded appliance? Yes. Stray voltage wants to go somewhere; and it will follow the path of least resistance.

In your illustration, yes, you will read voltages at all points shown. Voltages will be different at different distances and moisture and mineral content. However, I find it hard to believe that 5,000 miles away you'll be able to pick up any sign of that particular circuit. You may find voltages from other sources. Static voltages can be in some surprising places. And if you've ever studied lightning strikes you may be aware that there are several tendrils of electricity reaching down while at the same time several more reaching up. When one meets - THAT becomes the path of least resistance to ground (earth). Still, if you happen to be caught in one of the tendrils that don't complete the circuit you can still get a serious hit by the lightning. Many people who've been hit by lightning and survived have been struck by this very form of it.

But lets keep it simple. Grounding the generator AND grounding the appliance means if there's a voltage leakage (or a bare wire comes in contact with the casing) the voltage will flow through ground - not you. And hopefully pop the breaker.

Yes, ground and neutral are the same thing. Only, neutral is the intended return circuit. Ground is there as a back up plan.

 

OK, some people disagree with me regarding how much loss there is through the ground (earth). I'm not the expert here - so if I stand corrected then I stand so. After all, the earth is filled with minerals we mine and turn into conductors. So maybe you CAN find nearly full potential 5000 miles away from the source. I just hope you learn something.

 

A good ground resistance is 5–10 ohms

Sounds about right I don't no about 5000 miles the grounding on a 0ne wire sys is at each pole voltage is dropped But in my case as boy I learned that ground could be use as the return for power. We had one wire sys.
All you have to do is plug in a light and cut the neutral great way to mess up a pair of linesman pliers.
Ground is for safety

 

Come to think of it - my garage is wired for 240. It has one black wire (US) and one white wire. There's also half a dozen 120 V plugs on their own circuit. The 240 "Neutral" (or ground) was tied to an aluminum grounding rod. Just last year I had a problem with the 240. It turned out to be a bad grounding rod. I replaced it with a copper plated steel rod driven 7 1/2 of 8 feet into the ground. I've been running my table saw on one leg and the shop vac on the other. And I don't have to touch the regular 120 lines (which my saw and vac often blow the breaker).

 

Tony, I hope that I did not imply that we can not use ground as a return. The power to the houses on my street is powered by one conductor thru a transformer.

It's a matter of need/cost ratio. Only single phase is needed here. There is not enough ground loss to justify the cost of another conductor. The ground is free and no installation cost.

The higher you get the potential, the more this pays off.

Check out the DC long distance transmission lines. The high dc potential is inverted back into 3 phase at the destination.

The heartyness of the solid state devices is truly remarkable.

 

In 34 years I've seen transformers blow up house catch fire all because poor grounding or lost neutral.
A good ground will return power. and save you or your home we now have to install 2 grounding rods on every house.
I can see the OP having problems with AC There are lot's of miss understanding.

 

The original telegraph long distance system used only one wire for signal and the ground for the return.
Since the ground resistance varied with the terrain the battery voltage had to be changed to get proper operation, depending upon the location and line length.
Here's an article that discusses that.

 

No, I am not insulted. I'm not arrogant enough to think that every thing I say is going to always be the absolute epitome of knowledge. I'm here to learn - same as the next joe.

And there's a power pole in my yard with a transformer above. Lucky me! I hate overhead wires. There's a main guy wire grounding the neutral and there's two more ground wires (bare copper) estimated to be 8 or 10 gauge going down each pole in the neighborhood.

I know there's usefulness to using ground as a return but I just find it difficult to believe it can be effective over LONG distances. But like I said, I'm not the expert on such matters.

 

Take a look:
http://www.dummies.com/how-to/content/alternating-current-in-electronics-hot-neutral-and.html
Also watch this funny video to understand the difference between hot, neutral and ground.

 

V and v(t) are very different concepts.

v(t) where t=0 is a very different concept.

v(t) = A*(ωt+θ) is mathematically what comes out of the wall.

Let's not confuse this with the non-time varying Voltage that comes out of the wall. That might be 240 V RMS.

I want to go fill in the blanks above, but I'd rater not at this point.

Mathematically we can manipulate A*(wt+theta) to give us the RMS value. Again, I'll leave it alone.

RMS stands fro root _mean _squared. It does mean square the waveform, so the negative portions flip to the top and take the square root, so its ALWAYS positive and mathematically take the average.

Using 50*sin(x); the peak to peak value is 100 V.

The RMS value will be sqrt(50)/2 or around 35 Volts RMS.

These numbers work because the RMS voltage will be the equivalent DC voltage so ohms law works.

e.g P= VI; =240 RMS * 1 = 240 W;
240 VDC * 1 AMP DC = 240 W

Probably better to do in terms of ohms, but the numbers make the math work.

AC circuits with regard to power transmission is probably a poor place to start learning theory.

But Ground is the Earth - really. Dirt. It's the reference potential all around us or the one we would like.

It does turn out that the value of zero may be different 500 feet away when a storm is present.

But, we like the water pipes to be at zero volts and what we are standing on to be zero volts so we don;t get shocked. With pool, we have to out on a limb again. So, it a BAD place to start for fundamental concepts.

So, we bond the utility Neutral and Ground at one point and define 0 volts for the house/residence at ONE SINGLE POINT i.e. This point is 0 volts. We define it as that.

In the house, ground should not carry current except under fault conditions.
So, a hot wire touches a grounded case and the hot found an alternate path and it pops the fuse. It does do something detrimentally during the fault when parallel outlets are involved.

The point of this little exercise is really not to look at v(t) = 0, but the RMS value of the voltage entering the house. Peak to Peak is another way to describe it, but we won't do that either.

v(t)=A*(ωt+θ) is a way to describe this voltage. Theta is meaningless here unless we have a reference. ω is the radian frequency; so ω=2πf

If you looked at the voltage and the current of a resistor (resistive load), the phase relationship to each other would be identical.

When we need to make these measurements, again we define the reference.
Neutral is the conductor attached to that single earth point.

Any current flowing in the neutral won't raise the potential of the ground point since that point is made to be zero.

So, you now have concepts of RMS volts, Amps, peak to peak volts, phase angle, Earth. Ground, protective ground, hot and neutral.

Many complications have been left out.

So, Ground is really a reference.
Neutral is the normal current path to ground.
Hot is the non-grounded side of AC
Earth is really Earth. it's sometimes used to shield.

So, you kinda connect the ground reference to Earth. You use these differently even though they may appear to be the same point.

 

What exactly is the point of your question? ARE you asking.....that if we ground one side of a generator...........then measure from hot side of generator........................to ANY point on earth....that we would measure the same potential?

Yes! thats why I drew this picture. Notice that the ground that I added 50000 miles away, is just a copper rod attached to the earth, it is NOT connected to the rest of the circuit. Do you understand my problem? I want to know if this ground has the same voltage relative to the upper side of the load, as has the previous, closer ground that is attached to the circuit. I would like to think that the 50000 mile distance through the earth, could also be modelled as a resistor.?

 

Yes, the 5000 miles through the earth can be modeled as a resistor.

 

I don't think he get much voltage at 50 volts AC

 

I think you have still not fully grasped the idea of relative potentials and references. Here is an analogy that might help.

Take a meter stick and hold it vertically in the air. You know that one end of the stick is 1m higher than the other end of the stick. But you do not know how far it is off the ground. Now place the lower end on the ground. Now you can say that the higher end is 1m high (off the ground). Grounding one side of you generator is no different than that. It lets you change a relative voltage (or height) into a voltage or height above a reference point (ground).

Bob

 

I think you have still not fully grasped the idea of relative potentials and references. Here is an analogy that might help.

Take a meter stick and hold it vertically in the air. You know that one end of the stick is 1m higher than the other end of the stick. But you do not know how far it is off the ground. Now place the lower end on the ground. Now you can say that the higher end is 1m high (off the ground). Grounding one side of you generator is no different than that. It lets you change a relative voltage (or height) into a voltage or height above a reference point (ground).

Bob

I know that........... Why then physically ground one of the wires ? Since you can use any point on your circuit and call it 0V. Is it just for safety regarding the true ground in case the hot wire goes astray inside appliances??

 

Someone likely knows but I can speculate that it's to "protect" the neutral wires from becoming hot, as you mentioned. Connecting them to ground locally makes it just that amount less likely they could carry an unexpected and unsafe voltage.

Just to add to BobTPH's analogy, you could imagine a car battery powering a headlight. Connect one pole of the battery to a pipe thrust in the ground. What happens? Nothing. The light stays lit. Switch the connection to the other pole, what happens? Nothing. The light stays lit.

Connect them both, what happens? Unpredictable but the light probably dims and might even go out as the battery is shorted through the soil.

 

Someone likely knows but I can speculate that it's to "protect" the neutral wires from becoming hot, as you mentioned. Connecting them to ground locally makes it just that amount less likely they could carry an unexpected and unsafe voltage.

Just to add to BobTPH's analogy, you could imagine a car battery powering a headlight. Connect one pole of the battery to a pipe thrust in the ground. What happens? Nothing. The light stays lit. Switch the connection to the other pole, what happens? Nothing. The light stays lit.

Connect them both, what happens? Unpredictable but the light probably dims and might even go out as the battery is shorted through the soil.

Thanks for that.

Even though I can see that if we connect one of the wires to ground for satefy in case appliance cases touch the hot wire, and in that case, current could flow from the appliance through your body and through the soil and back to the neutral grounded wire, thus completing a circuit and hurting you by pushing current through your body. Is the resistance inside the human body + soil not high enough to block the current ? Can you give me a calculation that makes Sense?

Let's say the total resistance of the human body + soil path back to ground is 10 000 Ohms, if the voltage is 220V, then by Ohms law, the current through your body is about 0.022 Amps. is that enough to kill/hurt ?

 

Is the resistance inside the human body + soil not high enough to block the current ? Can you give me a calculation that makes Sense?

Let's say the total resistance of the human body + soil path back to ground is 10 000 Ohms, if the voltage is 220V, then by Ohms law, the current through your body is about 0.022 Amps. is that enough to kill/hurt ?

Oh yes! Have you never stuck your finger in a light socket or otherwise touched a live wire by accident? You don't forget it. And that's wearing shoes, standing on a non-conductive floor. In bare feet on the ground, I can't imagine.

We had a thread here not long ago about this very topic, about how dangerous it might be to touch the mains. Many, many people do it and survive, but that is not a recommendation! At the least it is very unpleasant and at the worst, fatal. People walk outside in lightning storms and swim with sharks and survive, but those risks are still very real.