The neutral and my understanding.

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mivey said:
If you get the return path worked out with Randy it improves the analogy.
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How about 2 tubes, one each direction connected with a u at each end. They are filled with balls that alternate with nec questions and answers. Then when the internets goes down, Bob and randy can still talk code.....that gets you the return but is still dc, unless they go back on forth on the same question which never happens cuz the nec is perfect
 
electrofelon said:
There isnt a magical place where "voltage is zero." We can tap a transformer winding anywhere and make that a grounded conductor, or even take a phase and ground it making a grounded conductor.
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After the ping-pong balls, I'd like to revisit something-

Voltage can only exist or be measured between two points, so there isn't any one place where the voltage is zero. We pick a spot, call it neutral/ground/reference/Fred and measure from there, but all of the names are just handy ways to talk about that particular spot.

Once we've picked that spot, we might do something with it, like bonding to the equipment grounding conductor (EGC). That does make it more special, but only because we want it to be.

(And while I'm at it.... consider Ohm's Law and the relations of voltage, resistance, and current. For instance, if you don't have any resistance, you can't also have a voltage to measure: Voltage = Current times Resistance.)
 
Chrisasks said:
So As as power flows from let's say phase "A" through a 277v 20ampere device and the unbalanced load returns through the neutral (no other loads connected for simplicity) all the way to the neutral tap on the transformer, where does the flow stop?

Ive read a lot that says it goes to ground and that's it,
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Currents don't just go to ground and done.

All currents find a way back to there source
either thru grounding somewhere
or even thru mutual induction.

They just don't "go away".

:?
 
zbang said:
After the ping-pong balls, I'd like to revisit something-

Voltage can only exist or be measured between two points, so there isn't any one place where the voltage is zero. We pick a spot, call it neutral/ground/reference/Fred and measure from there, but all of the names are just handy ways to talk about that particular spot.

Once we've picked that spot, we might do something with it, like bonding to the equipment grounding conductor (EGC). That does make it more special, but only because we want it to be.

(And while I'm at it.... consider Ohm's Law and the relations of voltage, resistance, and current. For instance, if you don't have any resistance, you can't also have a voltage to measure: Voltage = Current times Resistance.)
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And often the "zero" reference is any point of the circuit that is at earth potential, but it really can be at any point.

Ground a phase conductor instead of the neutral and your neutral is still the same in regards to the phase conductors but is now 120 volts (in OP's example) difference from the ground reference.

As has been mentioned already the system can be grounded at any point. For NEC applications however the neutral point of that particular system will normally be required to be the point that gets grounded.
 
JFletcher said:
I was thinking that the electricity returned to the source, THE source, that being the poco's generator windings.
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Current is only returning to the generator windings from one generator output pole up until the first transformation - then you effectively have a new source every time it is transformed, also called "separately derived system".

So at the typical utility customer location customer current is trying to return to the transformer it originated from. The primary current of that transformer is trying to return to the transformer in the next level up substation ... and so forth.
 
jerryalan said:
a ships hull is in contact with water and is sometimes used as ground . . .
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A ship is not covered by NEC and NEC definition of/or containing ground, grounded, grounding.... do not apply to the ship. Whatever standards apply may still call that "ground" though.

Shore power to the ship when docked is covered by NEC.
 
Chrisasks said:
This is my first post, and I've heard there are some on here with great wisdom!

I am in my fourth year of commercial, and am trying to learn all I can on both the theory side and install side.

Today's question: I've been studying transformers and neutrals and bonding.

I would love to get a greater understanding on the flow. thinking in terms of wye, I get that power is stepped down, three legs of 120 happen and a neutral is tapped at a point in the coils where voltage potential is zero. I also understand that in most cases, this zero potential tap is bonded to the ground at the transformer to bring the surrounding area up to that zero voltage potential(correct?). What's more is that it's known that the first means of disconnect bonds neutra bus to ground bus to create a safety path, then are kept separate from there forward, and that the ground should not interact with the power after that.

So As as power flows from let's say phase "A" through a 277v 20ampere device and the unbalanced load returns through the neutral (no other loads connected for simplicity) all the way to the neutral tap on the transformer, where does the flow stop?

Ive read a lot that says it goes to ground and that's it, done and I have trouble thinking that is sufficient as there would be extreme electrolysis and arcing and such as the ground's electrolytes were consumed.

Lets say the whole system was never bonded to ground and we were in a perfect environment where the load was isolated by insulated covers and such so that we could not get shocked and be ok, would the the neutral behave similarly?

Thanks for your time to all of those involved.
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There is electromagnetic radiation, direct energy transfer through a conductor, and the physical effect of what the electron may actually be doing.

Electron mobility, its actual movement, is very slow. You can walk faster than one specific electron actually moves in copper wire. What travels at the speed of light is the electromagnetic energy transfer, the EM wave. Charges in motion radiate EM by Maxwell's laws, the effect that results is Faraday or Lenz. The radiation travels at light speed.

In the ping pong ball analogy. the ping pong ball travels about ten feet but the effect travels at light speed. It is EM radiation, theoretically no mass is required for energy transfer, a (massless) photon is received.

Looking at the Sun and seeing light, feeling heat, it is the same effect. At the Sun there is an energetic reaction that charges the local electron to a higher energy level and it falls back to its more stable state, repeating again. Charging the electron is the absorbtion of a photon, falling back to a lower energy level the electron radiates out a photon.

That energetic electron never travels to you, but you are coupled to it and see, feel the effect because the EM wave does travel to you, the photon of massless energy (along with some cascade reactions along its journey, the atmosphere filters out and absorbs, reradiates, the more harmful energetic EM).

Certainly there are mass carrying space particles, electrons, protons, but conventional sunlight, heat, is pure massless EM radiation.

In an electrical power circuit, it is Kirchoff's and Ohm's law. If you have an open circuit, all the voltage drops across the open and no current flows. The open circuit does not radiate energy at the power levels of the sun or of the closed circuit.

The closed circuit, the conductor is the coupling method between the power source and the load. It is a coupling of energy conversion equipment types.

Grounding (bonding and Earthing) the transformer secondary only at a single point and only one time, the circuit is open and no current should flow. But the system is referenced to ground which limits its above ground high lines to the supply voltage and the transformer turns ratio winding. This keeps the system within the insulation rating of voltage to earth. Without this earthing, the insulation voltage rating may be exceeded relative to the Earth.

Connecting the system to ground at more than one point will cause current to flow, either neutral current in parallel over the ground or line side fault to ground.

There's a lot going on and it's a fascinating area of study.
 
__dan said:
There is electromagnetic radiation, direct energy transfer through a conductor, and the physical effect of what the electron may actually be doing.

Electron mobility, its actual movement, is very slow. You can walk faster than one specific electron actually moves in copper wire. What travels at the speed of light is the electromagnetic energy transfer, the EM wave. Charges in motion radiate EM by Maxwell's laws, the effect that results is Faraday or Lenz. The radiation travels at light speed.

In the ping pong ball analogy. the ping pong ball travels about ten feet but the effect travels at light speed. It is EM radiation, theoretically no mass is required for energy transfer, a (massless) photon is received.

Looking at the Sun and seeing light, feeling heat, it is the same effect. At the Sun there is an energetic reaction that charges the local electron to a higher energy level and it falls back to its more stable state, repeating again. Charging the electron is the absorbtion of a photon, falling back to a lower energy level the electron radiates out a photon.

That energetic electron never travels to you, but you are coupled to it and see, feel the effect because the EM wave does travel to you, the photon of massless energy (along with some cascade reactions along its journey, the atmosphere filters out and absorbs, reradiates, the more harmful energetic EM).

Certainly there are mass carrying space particles, electrons, protons, but conventional sunlight, heat, is pure massless EM radiation.

In an electrical power circuit, it is Kirchoff's and Ohm's law. If you have an open circuit, all the voltage drops across the open and no current flows. The open circuit does not radiate energy at the power levels of the sun or of the closed circuit.

The closed circuit, the conductor is the coupling method between the power source and the load. It is a coupling of energy conversion equipment types.

Grounding (bonding and Earthing) the transformer secondary only at a single point and only one time, the circuit is open and no current should flow. But the system is referenced to ground which limits its above ground high lines to the supply voltage and the transformer turns ratio winding. This keeps the system within the insulation rating of voltage to earth. Without this earthing, the insulation voltage rating may be exceeded relative to the Earth.

Connecting the system to ground at more than one point will cause current to flow, either neutral current in parallel over the ground or line side fault to ground.

There's a lot going on and it's a fascinating area of study.
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This whole area of science is as yet to be well understood. The idea of a required return path is a half baked idea IMHO. EM radiation does NOT require a return path. Shine a flashlight in the dark to observe this. This is the rock that drove Nikola Tesla to a nervous breakdown and he actually had to throw in the towel on his energy transfer over the earth (globe) concept after brutal work for 10 years in Colorado Springs and NYC. It was his persistence in trying to get this concept to work and his neglect of radio telegraphy which JP Morgan was giving him some money for that caused JP to stop funding him. Tesla was the best mind that worked this problem but he did not and we still do not have a plausible model even with all of the Physics research to date. Yes we get things to work but it is early days. We have to endure magnetic pole shifting and direct hit massive sun flares. We are now way out on a branch with out internet dependency so some caution is required. This takes a lot of study but here is a start from Wikipedia and will direct those interested to further study:

"Wardenclyffe Tower (1901–1917), also known as the Tesla Tower, was an early wireless transmission station designed and built by Nikola Tesla in Shoreham, New York in 1901-1902. Tesla intended to transmit messages, telephony and evenfacsimile images across the Atlantic to England and to ships at sea based on his theories of using the Earth to conduct the signals. His decision to scale up the facility and add his ideas of wireless power transmission to better compete with Guglielmo Marconi's radio based telegraph system was met with the project's primary backer, financier J. P. Morgan, refusing to fund the changes. Additional investment could not be found and the project was abandoned in 1906 and never became operational.
 
mivey already said it, but I want to emphasize a couple of points.

1) Ignore for a moment that we have alternating current. When the electrons flow out of a phase terminal and through the circuit, they then return to the neutral point...but they don't sit there; they flow through the transformer winding back to the phase terminal. When the current flows in the other direction, the electrons flow out of the neutral, through the circuit, return to the phase terminal, and then flow through the transformer winding back to the neutral point.

2) The neutral point is _not_ at zero volts. Grounding is what ties the neutral point to the local earth voltage. You could arbitrarily ground _any_ of the transformer terminals and the system would function. (It would not necessarily be code compliant, but it would function.)

-Jon
 
winnie said:
mivey already said it, but I want to emphasize a couple of points.

1) Ignore for a moment that we have alternating current. When the electrons flow out of a phase terminal and through the circuit, they then return to the neutral point...but they don't sit there; they flow through the transformer winding back to the phase terminal. When the current flows in the other direction, the electrons flow out of the neutral, through the circuit, return to the phase terminal, and then flow through the transformer winding back to the neutral point.

2) The neutral point is _not_ at zero volts. Grounding is what ties the neutral point to the local earth voltage. You could arbitrarily ground _any_ of the transformer terminals and the system would function. (It would not necessarily be code compliant, but it would function.)

-Jon
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And to round this out, we can look at the special case of the balanced wye. The three phase terminal currents are equal but out of phase and so add up to zero.
That means that at the load itself no net current flows from the neutral point back to the neutral point of the transformer. But at the transformer the current at any given moment flows from one winding to another through the neutral point. The net current between the load neutral point and the source transformer neutral point is zero, but in both cases line current flows in and out of the neutral point through each of the wires connected to it locally.
 
I thought the "effect" of electricity, although fast, does not travel at the speed of light. I thought that although all generation in a given grid interconnection are "synched", different points on the grid will peak at different absolute times (more substantial than just the speed of light). Is this correct?
 
electrofelon said:
I thought the "effect" of electricity, although fast, does not travel at the speed of light. I thought that although all generation in a given grid interconnection are "synched", different points on the grid will peak at different absolute times (more substantial than just the speed of light). Is this correct?
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Yes but don't mix the wavelength with the "effect". The effect is not quite light speed but close enough for this perspective. Even a slight move along the waveform (a change in phase) propagates at "effect" speed (might be 0.8C plus or minus). Effects propagate fast enough that the wavelength can be thought of as more positional, so peak to peak is spread over something like 3000 miles (don't feel like calculating precisely).

I have posted before on response times, even on the settling times of a change like a step function. IIRC it was on the order of a few light cycles before the circuit essentially settles from "sloshing" to a new state.
 
winnie said:
mivey already said it, but I want to emphasize a couple of points.

1) Ignore for a moment that we have alternating current. When the electrons flow out of a phase terminal and through the circuit, they then return to the neutral point...but they don't sit there; they flow through the transformer winding back to the phase terminal. When the current flows in the other direction, the electrons flow out of the neutral, through the circuit, return to the phase terminal, and then flow through the transformer winding back to the neutral point.

2) The neutral point is _not_ at zero volts. Grounding is what ties the neutral point to the local earth voltage. You could arbitrarily ground _any_ of the transformer terminals and the system would function. (It would not necessarily be code compliant, but it would function.)

-Jon
Click to expand...

To illustrate this, you can check out some of these old TV Ontario videos on Electricity from the '80s. The one on potential difference explains point 1) very nicely using skiers. Point 2) can be thought of as returning to the bottom of the ski lift. The ski analogy is for a battery, but replace it with a transformer or generator and it still works.

https://www.youtube.com/playlist?list=PLdIVKwXe8Up9z0pJGe0oLY5-yLbsaz_b7
 
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