Help understanding neutral conductor.

[Smart $]

6.28 x 10 to the 18th electrons per second

Multiply that by 1/120 of a second—the time elapsed during one half cycle at 60 Hz. This is the number of electrons per ampere passing any imaginary cross-sectional plane in the circuit going in one direction then reversing direction for the next half cycle.

Question: What volume of copper contains this number of free electrons, that is, if we assume each copper atom only let's one of its electrons be a charge carrier?

 

[quogueelectric]

coulomb

coulomb

Multiply that by 1/120 of a second—the time elapsed during one half cycle at 60 Hz. This is the number of electrons per ampere passing any imaginary cross-sectional plane in the circuit going in one direction then reversing direction for the next half cycle.

Question: What volume of copper contains this number of free electrons, that is, if we assume each copper atom only let's one of its electrons be a charge carrier?

You dont like Cows or coulombs???? Do you mean the valence electron or the charmed quark?? How many cubic feet of dirt in a hole 1 foot x2foot x3foot deep??

 

[Smart $]

You dont like Cows or coulombs????

I thank Cows for the milk in my 'fridge' and the majority of beef that I eat.:grin:

As for coulombs, what do they have to do with the question?

Do you mean the valence electron or the charmed quark??

See the image on this web page, then visit at least the two previous pages using the Back button within and near the top left of the page.

How many cubic feet of dirt in a hole 1 foot x2foot x3foot deep??

0 ft^3

 

[Twodollar]

Question: What volume of copper contains this number of free electrons, that is, if we assume each copper atom only let's one of its electrons be a charge carrier?

since copper has 8.5e22 atoms per cm^3 there are 6.28e18 electrons in 7.39e-5 cm^3 of copper.

*shrug*

 

[e57]

I thank Cows for the milk in my 'fridge' and the majority of beef that I eat.:grin:

You need a new butcher...

 

[Smart $]

I thank Cows for the milk in my 'fridge' and the majority of beef that I eat.

You need a new butcher...

So bull and steer meat no longer counts as beef?

 

[quogueelectric]

Its getting hot in here

Its getting hot in here

That was a nice presentation for the copper atom and the valence electron. Did someone say Butcher?? Im gonna go on the Lamb for now.

 

[Smart $]

since copper has 8.5e22 atoms per cm^3 there are 6.28e18 electrons in 7.39e-5 cm^3 of copper.

*shrug*

Your coulomb conversion factor is off. It is 6.24e18, not 6.28e18... however I do see that quogueelectric first posted the incorrect value—which I didn't catch at the time.

Nevertheless, I came up with 7.375e-5cm?.

Anyway, the following is the reason I asked...

Atomic Volume of Cu = 1.182e-29m?
Coulomb = 6.241e18 elementary charges (electrons, protons)
Assumption: 1 negative elementary charge/Cu atom (i.e. 1 free electron per atom)

1A = 1 coulomb/sec = 6.241e18 electrons/sec
6.241e18 ? 1/120 sec/60Hz halfcycle = 5.200e16 electrons/halfcycle
5.200e16 ? 1 atom/electron ? 1.182e-29m?/atom = 6.146e-13m? = 6.146e-4mm? (volume)​

Given the cross sectional area of a 12 AWG wire is 3.31mm?, a 1 amp current would mean the electrons travel an average distance of 6.146e-4mm? ? 3.31mm? = 1.85e-4mm...

...or a whopping 0.00000731 inches per ampere at 60Hz.​

Of course the above is an overly simplified method of calculating electron drift, but it suffices for the purpose of demonstration :grin:

 

[quogueelectric]

Inspiring

Inspiring

That is much slower than I had imagined ,Thank you for the explanation to better understand electron drift. I truly enjoyed the sarchasm thought provoking yet not insulting NICE!

 

[e57]

So bull and steer meat no longer counts as beef?

I didn't even think of that part of it - but goat, horse and wood chips defininately do not count as beef.

 

[Dennisc]

If we happen to add matching wattages of 1.5-volt bulbs to the two 1.5-volt halves of our 3-volt system, no current will flow through the wire to the center tap. However, if we have an imbalanced set of loads, the difference current will flow on the neutral.

All the help has been great, but I have one more question. I understand what is happening on just one circuit. What happens though when you have say a total of 20 circuits. 8 are on one 120 vollt line and 12 are on the other 120v line with totally different voltage. How does each neutral of each circuit work to balance out the system. Thanks for all the information. DennisC

 

[ronaldrc]

Here is a Picture of what the battery circuit would look like they have been discussing


We still can not see the particles that make up electricity.

We are just now entering nano technology maybe after a few decades into this field we will have nano computers or machines that will be able to communicate to us what electricity is and exactly how it works.

But untill then I like to use water flowing in a pipe as an analogy for electrical flow the effect of volume of water is the same as amperage in electrical and pressure the same as voltage in electrical.

 

[Smart $]

What happens though when you have say a total of 20 circuits. 8 are on one 120 vollt line and 12 are on the other 120v line with totally different voltage. How does each neutral of each circuit work to balance out the system.

Assuming all circuits to be of the same ampacity and conducting at the same amperage, in typical split phase distribution, two circuits?one from each line?will share a neutral conductor (aka multiwire branch circuit), at least to the point where the individual circuits go their separate way. From the source panel to the point of separation, the neutral conductor will carry the difference in current of the loads, which would be zero amperes by the original assumption. From the point of separation to the loads, the neutral conductor will carry the full current of the respective connected loads.

The above would take care of 16 of the circuits you ask about, 8 on each line... provided they are wired as three-wire circuits. The other 4 circuits will typically be individual [branch] circuits because of the criteria you stipulated, where each will be two-wire circuits from the source panel to their respective loads and both wires of each circuit will carry the full current of their connected loads.

Generally speaking, these 4 individual circuits would imbalance the panel, it's feeders, and perhaps go all the way back to the transformer. As such, the circuits would typically be rearranged so as to balance the accumulative loads on the two lines... and in doing so may permit them to be run as three-wire circuits.

While many novices consider the panel as the source, it is not. Usually the source is considered to be an "upstream"(i.e. line side) transformer (even though the ultimate source is usually the poco/grid generators). From the transformer to the panel are either service conductors or feeders, or both, with at least a main disconnect and overcurrent protection added in somewhere along their path. These conductors will carry all the current of your 20 circuits. As we are assuming all 20 circuit loads are equal, the neutral feeder/service conductor will carry the load of 4 circuits all the way back to the transformer.

 

[LarryFine]

What happens though when you have say a total of 20 circuits. 8 are on one 120 vollt line and 12 are on the other 120v line with totally different voltage. How does each neutral of each circuit work to balance out the system.

First of all, the voltages (assuming a properly-working system) would not be "totally different", but the amperages would be. The quantity of circuits is totally irrelevant.

Any load is subject to the voltage between the conductors to which it is connected, the resistance to current flow is whatever it is, and the resultant current can be calculated using Ohm's Law.

To find the system neutral current, you would simply add the actual current usage (not the breaker rating) of each circuit connected to each hot wire, and find the difference between the two totals; that's the neutral current.

By the way, just to keep the technical terms straight, the grounded conductor of a circuit is not really a "neutral" unless it is the grounded condcutor in a circuit comprised of more than one ungrounded conductor.

In any case, the current in a two-wire circuit's ungrounded and grounded conductors will normally be identical. Only a shared neutral carries "balancing" current.

Otherwise, the grounded conductor simply carries the same current as its hot wire. In fact, the operation of a GFCI device depends on this fact to detect when an accidental contact with a hot wire occurs.

 

[jetlag]

circuit with hot wire only

circuit with hot wire only

Ran across a very old barn one time, owner only had property a short while and complained the light in barn is dim no matter what watt bulb he uses. I noticed there was only a single wire overhead to barn . looking closer I saw where another wire had been broken off the insulators on both ends , probable from fallen limbs. Out at the barn some one had taken the neutral wire which used to exit the barn and connected it to a galvanized pipe driven in the ground. The bulb seemed to burn about half wattage or a little more. I thought about how this could be and decided to take the ground wire off the ground rod over at main house and see if the bulb went out. The bulb got dimmer but kept burning. My thoughts were the current now has to travel more distance to power pole ground and back up to the transformer. Ive often wondered if I went up the line removing the grounds would the get dimmer and finally go out or if some way would keep burning by going up the neighbours ground to the transformer? Might not answer your question but its a start. I ran another neutral wire and a ground to the barn.

 

[alachabre]

That's a popular misconception, Charlie. Actually, current is much, much, much slower.

<snip>

While current may be slow, its effect is not. As a matter of fact, it is [nearly] instantaneous because electron drift occurs at all cross sections along the circuit path [nearly] simultaneously.


I've read this thread with great interest. It's apparent there is much in the way of misunderstanding of basic concepts, and that attempts at clarification can get carried away pretty quickly. I'll put this as simply as I can:

Current is measured in Amperes which is defined in terms of Coulombs per second.

A Coulomb is a measure of quantity of charge, not quantity of electrons.

The number of free electrons available per given material and the strength of the applied electric field are factors in determining the quantity of charge, all of which is directly related to drift velocity.

So we can now state: current is fast, electrons are slow.

 

[Dennisc]

O.K. now I understand, it finally clicked! I some how got the idea that in a normal two wire circuit that the white was a neutral, but now I understand that it would carry energy back to the panel. I guess a neutral would be like on a 220 v 3 wire hot water heater. Black and red hot, then white neutral. Sound Right? This type of "neutral" is what would handle the imbalance. All the help was great. Like I said, I am not a electrician, I just finished my first class in basic electricity. Now understanding this; I will be able to sleep better tonight. Thanks to all the pros. for helping a newby.
Thanks DennisC

 

[LarryFine]

I guess a neutral would be like on a 220 v 3 wire hot water heater. Black and red hot, then white neutral. Sound Right? This type of "neutral" is what would handle the imbalance.

Dennis, you just happened to pick the wrong type of appliance as an example, because a water heater uses the two hot wires only. The heating elements are rated at 240v, there are no 120v components in a water heater, so a 2-conductor + g. cable is appropriate.

Now, a clothes dryer is the perfect example, because while the heating element is rated at 240v, and connects line-to-line, but the drum and timer motors are rated for 120v, and connect from one line conductor to the neutral. A 3-conductor + g. cable is called for.

So, for a dryer, both lines would carry the heater current; in addition, one of the lines and the neutral would carry the motor loads. If the heater is 20a and the motors total 5a, then one line would carry 20a, one line would carry 25a, and the neutral would carry 5a.

 

[Smart $]

That's a popular misconception...

...So we can now state: current is fast, electrons are slow.

...and the misconception is perpetuated

 

[winnie]

For conduction in copper wire:

The aspect of current that is _net_ flow of charge is _fast_ (moving at a large fraction of the speed of light). If you have a loop of conductor many miles long, and you apply a potential at the near end terminals, and measure the current flowing at the near end terminals, you will measure the same current flow at the far end of the loop, with a delay that is of the same magnitude as it would take light to reach the far end measurement location.

Any measurement or definition of current that depends upon the _net_ flow of charge will demonstrate that current moves very quickly.

The aspect of current that depends upon the rate of movement of specific charge carriers is _slow_, in fact very slow.

Any measurement which depends upon the rate of charge carrier flow, it will measure a very low velocity.

An example of such a measurement is 'hall voltage', the voltage induced across a conductor in a transverse magnetic field. When a charge carrier moves in a magnetic field, it is pushed in a direction that is perpendicular to both the direction of motion and the magnetic field. This produces a voltage across the conductor, which can be measured. http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/hall.html

I generally hate the electricity as water flow analogies, but consider this: given a pipe with water flowing through it at a rate of 1000 gallons per minute, would you say that the water is flowing quickly or slowly? How about if I tell you that the pipe is 1" in diameter? How about 200" in diameter?

I don't see how you can say current is fast or slow without explicitly defining what aspect of charge movement you are calling current. If you use the SI definition of the Ampere, you are using _net_ flow, which is clearly fast. If you are using the actual movement of charges, then it is clearly slow.

-Jon