Electron flow in 240V circuits

mbrooke

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A & N can have potential to all kinds of stuff. Without a circuit path to that stuff, the charges flowing in A & N will NEVER try to flow to the other stuff.

The 10 amp neutral current on George's circuit CANNOT flow to C. It will never happen. It is mathematically and physically impossible.

Just because C exists in the world does not mean something is going to use it. Just because we have three-phase available does not mean current to a single-phase load will try to eventually travel through all three phases. That is what George proposed and it is completely and utterly wrong. Fundamentally and any other way you want to look at it.
I think George was saying the potential existed and if you connected a load to C thats what would happen. But yes its true if you only had load on A and B it would never get back on C no matter what.
 
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George Stolz

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Mivey, you sure put up a lot of words there but you're missing (while confirming...?) my point.

I have three lamps, all connected phase to neutral. All lamps draw 10A of current. They are supplied from circuits 1, 3, and 5. As I turn them on in sequence, why does the current disappear from the common neutral when the third breaker is closed? If the preferred destination were not the phases, wouldn't it show 10A on all four conductors - all phases and neutrals - using the neutral on different wavelengths averaging 10A overall? Why can I open the neutral with even loads on all circuits and the lights stay evenly supplied?

Your novel about dump trucks and pickups and so on did not clarify your ire about my simple analogy. I have not claimed it was perfect, but I did not think it was on par with "electricity seeks earth." In fact, I take exception to that because my lead in to using this animation in class is to firmly refute the earth's role in normal current flow.

I'd hate to sow a bad seed, but you're not making your case well enough to inspire me to edit it.
 

ggunn

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Mivey, you sure put up a lot of words there but you're missing (while confirming...?) my point.

I have three lamps, all connected phase to neutral. All lamps draw 10A of current. They are supplied from circuits 1, 3, and 5. As I turn them on in sequence, why does the current disappear from the common neutral when the third breaker is closed? If the preferred destination were not the phases, wouldn't it show 10A on all four conductors - all phases and neutrals - using the neutral on different wavelengths averaging 10A overall?
Different wavelengths? It's all 60Hz, isn't it?
 

jaggedben

Senior Member
...I have three lamps, all connected phase to neutral. All lamps draw 10A of current. They are supplied from circuits 1, 3, and 5. As I turn them on in sequence, why does the current disappear from the common neutral when the third breaker is closed? ...
Because the current flow on the neutral cancels out. mivey is correct that the current for A-N and B-N loads isn't trying to go to C if there is no connection through a load (or a short) connected to C.

I do believe this is mostly semantic as long as we're discussing it using only words and not mathematical formulas.
 

Strathead

Senior Member
I have to agree with George and iWire. mivey is trying to make sure the OP has majored in physics BEFORE he is allowed to get his mind around the basic concept of electrical flow. The Besoker has to through in the part about electrons wiggling. When I first read George's analogy, I thought is was pretty good. It models most of what happens. I don't need to know A square+B square= C square to know that a pair of 30 degree bends 20 inches apart produces an offset of 10" And while I hope my apprentice continues learning and finds out how to use Pythagorean's Theorum right now I just want him to make a bunch of 10" offsets. Same thing with getting ones mind around 3 phase current flow.

electro7 As has been pointed out, at least in the current theory, an electron doesn't actually move from one end of the circuit to the other end of the circuit. Suffice it to say that energy, not a particle does the moving. For what you are trying to understand in basics, IT ISN'T IMPORTANT, but since it was brought up. Think of a tube filled with water and a balloon ion each end. If I squeeze one balloon, the other one fills up right? But is the actual water particles from the first balloon? No, but who cares.

When I am troubleshooting I always think of myself as a single electron starting at source and running around trying to get back to source. It has worked for me for 25 years, or more, even though I know what mivey and besoker are saying is technically right.

Stick with Gearoge's analogy. And if this helps. He didn't mention cancelling. If I have 10A flowing on A and 10A flowing on B in a single phase circuit, then where they "collide" they cancel each other out instead of travelling on the neutral. So there are 10 amps of flow, in the negative direction that is cancelled out by the ten amps of flow in the positive direction, but since the energy produced is still the same, Ohm's law says the voltage must double.

In a three phase circuit, the A phase and the B phase "collide" at an angle so some of the flow is diverted to the neutral, but most of it still cancels The mathematics of that is the whole square root of three thing (1.73), due to the phase angle. So the amount that is cancelled is amps divided by 1.73. The amount on the neutral is amps divided by 1.73 subtracted from the amps per phase, and the voltage increased is the per phase voltage times 1.73.

I believe once you get your head around it then you can move on to the depth that mivey is trying to get you to start with. I spent forever trying to understand how a transistor worked to amplify a waveform, but it wasn't until I used a "useless" analogy did I understand. Until then all the perfect theory and math they taught me went in one ear and out the other.
 

Strathead

Senior Member
"In the case of a 12 gauge copper wire carrying 10 amperes of current (typical of home wiring), the individual electrons only move about 0.02 cm per sec or 1.2 inches per minute (in science this is called the drift velocity of the electrons.)."

https://www.uu.edu/dept/physics/scienceguys/2001Nov.cfm
That is still part of the "THEORY OF ELECTRICITY" Here is a forum wherre people a lot more anal than me are arguing about it,
http://www.frihost.com/forums/vt-111205.html

And here is a link to a Harvard Professor disagreeing that 1 plus 1 always equal two.

http://news.harvard.edu/gazette/1997/01.16/When1and1AreNot.html
 

Strathead

Senior Member
Do you agree or disagree?
With what? 1 plus 1 equals two or the current theory of electricity? If it is number two then basically no. My money is on us being no smarter than dogs being taught Quantum physics. I don't believe we have advanced our understanding of the universe enough yet to truly grasp What electrons are and/or how they interact with each other.
 

mivey

Senior Member
Mivey, you sure put up a lot of words there but you're missing (while confirming...?) my point.
Well George, whether or not you learn anything is your responsibility, not mine. I am willing to help others learn but I can't drag someone kicking and screaming to a better understanding because knowledge requires effort from those who would aquire such knowledge. You can lead a horse to water but you cannot make it drink.



I have three lamps, all connected phase to neutral. All lamps draw 10A of current. They are supplied from circuits 1, 3, and 5. As I turn them on in sequence, why does the current disappear from the common neutral when the third breaker is closed?
Because the path back to the first phase has a lower energy solution THROUGH the other phases because the loads and phases work together. The other phases ARE NOT the destination but provide a shortcut, so to speak, back to the first phase.



If the preferred destination were not the phases, wouldn't it show 10A on all four conductors - all phases and neutrals - using the neutral on different wavelengths averaging 10A overall?
If you had 10A of incandescent on the first phase, 10A of motors on the second phase, and 10A of computers (or maybe a capacitive load if you could think of one) on the third phase then you will have neutral current because the phases don't all work together and some of the current will find a lower energy path through the neutral BACK TO IT'S ORIGINATING PHASE. The neutral current may even be on the order of 6-7 amps or more for a quick calc I just made.

Whatever route the current takes, when it reaches the common neutral point at the transformer, it goes back to the originating phase, NOT some other phase like your analogy proposes.

Also think what happens if you have 10A, 1A and 1A of similar type loads. The other phases only share their path to the extent that their loads are complementary. If the phases are the preferred destination then they would share their half of the 10A load but that is not the case as most of the 10A takes the neutral path. In fact they only share about 1A and the neutral takes about 9A.




Why can I open the neutral with even loads on all circuits and the lights stay evenly supplied?
Because IF the load on the other phases is complementary to the first phase, they can "carpool" so to speak and work together in a lower energy state. In other words, the current path back to the first phases has an easier route THROUGH the other phases, but the other phases are not the destination.

If the load on the other phases is NOT complementary, then the easier route back to the first phase is through the neutral. Note the destination for the first phase current is still the first phase.

If the load on the other phases is partially complementary, the some of the first phase's current will take a path through the other phases and some will go through the neutral. The destination is still the first phase.

In no case will current from the first phase that reaches the N point on the transformer seek to go through the windings to the other phases as your analogy states. That is where your analogy is wrong and where you are teaching your students incorrectly. It is up to you whether or not you can accept that bit of knowledge.



Your novel about dump trucks and pickups and so on did not clarify your ire about my simple analogy.
It may have seemed like a novel but I was only trying to help you understand.



I have not claimed it was perfect, but I did not think it was on par with "electricity seeks earth." In fact, I take exception to that because my lead in to using this animation in class is to firmly refute the earth's role in normal current flow.
I find it interesting that you would use an incorrect analogy about current destination to refute another incorrect idea about current destination and not see the correlation.

I also find it interesting that you use the same analogy in teaching a class that you have used here. Have you considered that you might have taken a defensive posture against changing your analogy?

The source the current seeks is not the other phases but its own originating phase. The current may or may not use a path through the other phases but the other phases are not the destination.



I'd hate to sow a bad seed, but you're not making your case well enough to inspire me to edit it.
I'm not sure I'm trying to make a case, just trying to pass along knowledge. If you want to continue thinking the destination for one phase's current is the other phases then no amount of information will change your thinking until you decide you want to know if that is actually true or not. For you to learn, you have to meet me part way or there is no exchange of knowledge.

I certainly appreciate the interaction on these topics, your replies, and the time to think on these things. But if it comes to where there is no exchange of knowledge, that would hold no interest for me at the moment.
 

JFletcher

Senior Member
Location
Williamsburg, VA
That is still part of the "THEORY OF ELECTRICITY" Here is a forum wherre people a lot more anal than me are arguing about it,
http://www.frihost.com/forums/vt-111205.html

And here is a link to a Harvard Professor disagreeing that 1 plus 1 always equal two.

http://news.harvard.edu/gazette/1997/01.16/When1and1AreNot.html
1 + 1 doesnt always equal two. Mix 500ml of 91% IPA with 500ml of water, and you do not get 1000ml of mixed solution due to the increase in specific gravity/density. And 1L of water at freezing mixed with another liter of supercooled water would yield roughly 2.1L of ice.
 

Ingenieur

Senior Member
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Earth
A couple of points
the movement of the electrons is not the energy transfer medium/mechanisn
see Poynting E cross B ~ energy /area / time
the fields transmit the energy
no E in the conductor so no energy
the electrons dance to Maxwell's music lol

does current prefer the phase or neutral?

the xfmr X0 zero sequence reactance presents a lower return Z than a phase
almost like a gnd fault limited only by 1 winding and the load
where as ph-ph is 2 windings and load

which allows more power flow
assume each load 12 Ohm per wye leg
120/208 vac

wye w/X0 neutral or wye (floating no neutral)?
 

mbrooke

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Because the path back to the first phase has a lower energy solution THROUGH the other phases because the loads and phases work together. The other phases ARE NOT the destination but provide a shortcut, so to speak, back to the first phase.

When you use the word short cut its basically saying electricity seeks the shortest path back to the source... In a sense the other phases are a destination, a point in the node that takes them back to the source. I think we are just nit picking terminology.



If you had 10A of incandescent on the first phase, 10A of motors on the second phase, and 10A of computers (or maybe a capacitive load if you could think of one) on the third phase then you will have neutral current because the phases don't all work together and some of the current will find a lower energy path through the neutral BACK TO IT'S ORIGINATING PHASE. The neutral current may even be on the order of 6-7 amps or more for a quick calc I just made.

Whatever route the current takes, when it reaches the common neutral point at the transformer, it goes back to the originating phase, NOT some other phase like your analogy proposes.

Also think what happens if you have 10A, 1A and 1A of similar type loads. The other phases only share their path to the extent that their loads are complementary. If the phases are the preferred destination then they would share their half of the 10A load but that is not the case as most of the 10A takes the neutral path. In fact they only share about 1A and the neutral takes about 9A.
I agree on this. Energy out of one phase winding is always the same amount of energy going in that same phase winding.
 

mbrooke

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I find it interesting that you would use an incorrect analogy about current destination to refute another incorrect idea about current destination and not see the correlation.

I also find it interesting that you use the same analogy in teaching a class that you have used here. Have you considered that you might have taken a defensive posture against changing your analogy?

The source the current seeks is not the other phases but its own originating phase. The current may or may not use a path through the other phases but the other phases are not the destination.

And oh, not saying your wrong. But consider a 25kw 208 load connected phase A-B. Don't the electrons use source B winding to get back to source A winding and visa versa?
 

mivey

Senior Member
When you use the word short cut its basically saying electricity seeks the shortest path back to the source...
Short cut not by length but that it will seek a route that results in the least amount of energy being expended.

In a sense the other phases are a destination, a point in the node that takes them back to the source. I think we are just nit picking terminology.
It is not just about terminology but an error in thinking. Recall the OP premise is that A-phase current that reaches the N point on the end of the A-N transformer winding will turn and go through the C-N transformer winding to reach the other phase C.

That is fundamentally wrong, a bad analogy, should not be taught. Correcting that is not nit-picking.


Energy out of one phase winding is always the same amount of energy going in that same phase winding.
Energy is not leaving one terminal and returning on the other; that would be current. The moving charges don't carry the energy. They create fields used for energy transport.

Moving charges (current) create magnetic fields and charge separation (voltage) creates electric fields.

Energy radiates out from both phase terminals towards the load and travels in the electromagnetic field.
 

mivey

Senior Member
And oh, not saying your wrong. But consider a 25kw 208 load connected phase A-B. Don't the electrons use source B winding to get back to source A winding and visa versa?
A & B terminals are opposite ends of one 208 volt A-B phase. Current leaving A matches the current into B. It is exactly the same current because it is a 2-wire circuit. Without the neutral there is only one current present and only one phase present.

That is not the same as having two separate 120 volt phases of A-N and B-N with associated L-N loads. With N present in this 3-wire circuit we now can have neutral current and current leaving A terminal may not always match current into B terminal. Unbalanced loads result in neutral current.

FWIW, even with a perfectly balanced set of loads, there will be miniscule neutral current because the two windings and connections are not exact duplicates. The current leaving A won't be the exact current into B but the difference is usually negligible.

Don't be confused by the loose use of the term "phase".
 
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