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120 VAC & The role of the neutral

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Cliff321

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What is the role of neutral?

I have read that: (A) The power alternates from + to - with the little electrons rushing back and forth and (B) that there is no back and forth but rather a pulsing from a + state to a Zero charge state.

I don't know which it is. But I suspect the role of the neutral will not tolerate one while it will facilitate the other.

Talismanic phrases like Center tap, Balancing, yadda yadda are tossed around on the interwebs with no explanation of the actual mechanics of what is going on.
What is going on?

In scenario A, I believe that the neutral would have to be charged (but it is not) in order to make the flipping of + to - happen or else there could be no rushing back and forth.

In B, I can picture the neutral acting like an open valve but still never being charged. Except for the fact that the electrons that are being pulsed from On to Off from the Mains are not being burned up in the appliance. Electrons are like those short squatty landscaper guys who scurry across insurance company green-scapes. They do work, but are not consumed. Where do they go?

Adding to my confusion is the fact that neutral is bonded to earth in the main panel, but never in a sub panel unless that sub panel is in an out building where it has it's own earrthing rod.


So what are the mechanics of the role of the neutral?

Any takers?
 
thanks for that.
Wisconsin Voc Tech is a pretty good source I should think.

Which one of those two lines in the SWF could be called neutral - if either one could?
And if one could, then what would happen if in that SWF one of those two lines was bonded to earth? You know, the way neutral is in a residential main panel. Wouldn't that screw up the circuit?

But there was no mention of the neutral.

So there is a + and a - phase. OK. What's happening to the electrons? Are they really reversing direction?

But I'm still stumped. I sort have a handle on simple DC circuits and I think that one axiom applies to both AC & DC: "Power will not flow absent a complete circuit"
And I think I get why the 240VAC circuit works- because the two phases are 180 degrees out of step with each other so while one is + the other is - and back and forth.


But what's the neutral doing in a 120 line?
The residential mains have a neutral line but in the main panel the neutral is bonded to the earth. If you bonded one of those two lines from the SWF you'd screw up the circuit - - yes?

Are you seeing my confusion? If the neutral were hooked to the generator like the two lines in that SWF, then the neutral would be charged - - yes~??
But the neutral is not charged.


And interestingly there is supposed to be some resistance in the delta between the neutral and the ground.


If I were I to test the neutral in a completed circuit such as the white line from a lamp while the lamp was energized would I detect line voltage?
Would I detect electric current if I tested the neutral and connected the other lead to ground?

Where does the neutral return to in the mains outside?
 
hi Cliff,

In the animation, you could connect either wire of the AC generator to EARTH, this would make that wire the NEUTRAL wire.

The other wire would be LINE or sometimes called PHASE. [its the 'HOT' wire].

In commercial SINGLE Phase networks one outgoing wire from the AC generator is connected to EARTH at the generator, this is known as NEUTRAL.

The NEUTRAL wire is also connected at other points in the distribution network in order to ensure that the NEUTRAL is held close to EARTH potential.

The AC current flows in alternate directions at a 60HZ frequency.

Does this help.??
 
hi Cliff,

In the animation, you could connect either wire of the AC generator to EARTH, this would make that wire the NEUTRAL wire.

The other wire would be LINE or sometimes called PHASE. [its the 'HOT' wire].

That clears up some of it. Thx


So then, the neutral is energized in a closed circuit? Hence the insulation on the wire?


Now about that ground wire that goes to earth and is bonded to the neutral in the main panel.

Given that the residential neutral is bonded to the earth, why then does not the bare ground wire experience an electrified state during normal operation?
Is earth not part of a complete circuit?
 
You're over thinking this ;)

It doesn't matter if it's AC or DC, thinking about electrons moving a specific way doesn't really help you at all (and just causes confusion).

Think simple! - a 6v battery, a 6v bulb, and two pieces of wire.

Connect one piece of wire from negative of the battery to the bulb, and the other from positive to the bulb - the bulb lights OK? - a normal circuit.

Now get a third piece of wire, and connect the negative wire to earth - the bulb still lights, nothing has changed, yet the negative of the battery is now 'neutral, and the positive is now 'live'.

Remove the third wire from negative and connect it to positive instead - yet again the bulb still lights, again nothing has changed, yet positive is now 'neutral', and negative is 'live'.

The basic fact is that everything you measure is 'relative' to something else (essentially where you stick the other end of your meter) - so if you connect your meter negative lead to the negative of the battery, then the positive of the battery will read positive regardless of where you connect an earth wire. However, if you connect the meter negative to ground, then the battery polarity will change depending which side you earth, because you're now measuring relative to earth, and not to a specific side of the battery.

The ONLY reason live and neutral exist at all is because the neutral is earthed, the two terms are 'relative' to earth, nothing else - exactly as with the battery/bulb example. As a service engineer I use isolation transformers on the benches at work, this breaks the neutral/earth connection (for safety reasons), giving two simple mains wires, neither of which is live or neutral as they aren't referenced to earth at all.
 
I think you are confused on two issues, ground and neutral. First the example did not explain 120/240. Generally in the US 240 is sent to the residence, but with a caveat. The 240 is produced from a transformer with a center tap. Other countries have distribution networks without a center tap. Second seems to the ground/neutral concept. In US residence wiring the Center Tap is grounded, and a very good ground indeed. It is grounded first at the transformer on the pole and again at the main distribution panel at each residence. When I say ground, I also mean earth as in a metal rod is stuck in the ground. This becomes the measuring reference point or standard for the rest of the residence. The black meter lead is always placed on this point (or its equivalent and all voltages are measured with respect to this point. It is also the GREEN wire in 3 wire residence wiring. The Black, Blue or Red wires are measured with respect to (WRT) this green wire, therefore they will read 120 from any of these to the green wire. The white wire is called NEUTRAL, this is sort of a misnomer as neutral indicates that it has or carries no charge. Nothing could be further from the truth. A more appropriate name for the white wire would be "RETURN" as it returns the current after it has been applied to a device. There is no current flow in the white wire, unless it has been applied to something, e.g. lamp, fan, stereo, refrigerator etc. However once one of these devices have been activated current will be flowing in the same quantity as was in the black, blue or red HOT or "source" wire. This white wire wends it way through the house and ends up in the distribution service panel where it is connected to the GREEN ground wire. Now if the wiring has been sized properly, the black and white wire will be low (less than 1 ohms) resistance. Virtually the same but not quite at the same potential as the green wire.
Lets pretend the white wire has .1 ohm of resistance, and we have a current of 10 amps. What is the voltage drop across the white wire
Ohms law E=IxR. So E=10 Amp x .1 Ohm=1 Volt. If you could measure this voltage you place the black lead on the green wire and the red on the white and you would see the 1 volt, but with a current of 10 Amps. If at the same time you measured the black wire you would see 119 volts (the black wire carries 10 amps and has the same resistance so it will also have a voltage drop of 1 volt. What will you read if you place the black meter lead on the white wire and the red lead on the black?
Hope this helped a bit. If I haven't confused you we will next go on to phase and US 240 VAC.
Finally do you have a car that is several years old? If yes, open the hood and look for the battery. The + terminal will have a couple of big red wires, the black maybe the same and a thinner wire that goes to the chassis. This will be a demonstration of ground and neutral. Make certain all your lights are operational, marker lamps, headlights, turn signals, brakes etc. This thin black wire is ground or neutral for your lighting circuits, turn the head lights on and the 4 way flashers. Leave the key in the off position. Now disconnect the thin black wire. Go check your lights. If your car is more than a few years old, you will see some interesting effects. If you measure the voltage from this wire to a good chassis ground, or the engine block you will see the difference between ground neutral and return. I suggested an older car as dirt and corrosion will be present on the various connections enhancing the effects. As you touch the thin wire to the chassis you may see a spark and all the lights return to normal.

A bit long winded but it can be a bit confusing. I worked with a guy in the service, this was his specialty, he had been working in the field for 18 years or so and still had some misconceptions. A quick note on phase, US has single and three phase. There used to be two phase, but I think it has mostly disappeared, it was primarily used in lighting circuits.
 
The "role" of the neutral does depend on where in the world you are. Particularly if 240/120 is supplied to to residential areas.

In the US, the Neutral carries the UNBALANCED current and can change direction. The US may call the residential wires L1, L2, N and Ground. If there are only 240 V loads, the neutral would have zero current on it. If the 120 V loads on L1 and L2 are the same, there will be zero current on the neutral.

If L1/N has 10 A and L2/N has 15 A, then 5A flows through the Neutral. If the currents on L2 and L1 are transposed, then the direction of the Neutral flow reverses.
 
Correct: That is why I specified USA residential wiring and only the 120 volt side. Even so, in my example of a 10 Amp load in a 120 VAC wall outlet, there is 10 Amps flowing in the white wire.
 
@JMW
Your post is a bit hard to read. Lots of run-on sentences.

I can also add, which white or what Neutral? 10 A would be present in the white and black wire that go to the outlet, yes.

I wasn't as clear as well. The NEUTRAL I was talking about is in a 4-wire (L1, L2, N and ground system) or the NEUTRAL conductor that is bonded to ground at the service entrance. Different animals, but the same concept.
 
The devil is in the details. It looks so simple on paper until.......... Sort of like that math homework problem. Spent hours on it and never did get it correct. The Teacher drew it on the board in 30 seconds and it made perfect sense.
Hopefully the OP is still alive and well.
 
OK then is the reason that the does the earth (ground ) wire in a residential US system is not energized because the resistance is so much greater to complete the circuit to actual earth than it is to the center tap on the line transformer?

Which might explain why I had all manner pf weird power surges and problems that day the neutral line from the power company failed - - it was because the neutral was no longer conducting, leaving the residential earthing to carry all the load and it couldn't?
 
Cliff:
The quick answer is no, but it can/may cause surges.
To quote Meatloaf, "I'll give you an answer in the morning"
 
In the above link, you have the 120/240 split phase. The earth ground in your home is not energized for the following reasons: A) The utility actually provides the ground at the transformer, and B) if the home is properly wired, there is no need. It only become energized if there is a fault; such as the motor in your refrigerator develops a short to ground. If the green earth wire is energized you have some sort of problem, it is a safety wire only.
Hopefully you understood our above posts before going on to split phase 120/240?
Are you good mechanically? can you wire a demonstration circuit, and do you have 50 bucks or so and a voltmeter?
This is going to take a bit of time so bear with me.
In your main distribution you will find the following; 3 heavy black wires, 1 of the black wires may have white tape and a green wire. The black and white wires go to the utility transformer, the green goes to a ground rod near the panel. The two black wires go to each power rail in the panel. You have two columns of circuit breakers correct? We will call the left column L1 the right column L2. The black wire possibly white tape goes to a bus bar it is called N. The green wire is also connected to this bus and this bus only. The metal panel is also connected via mounting bolts and star washers.
If the house is properly wired, the loads on the left and right circuit breaker columns are relatively equal. You will also see some large circuit breakers that take up two slots. These breakers access both power rails providing 240 volts for a stove dryer etc. Each circuit branch comes into the panel, (we are disregarding the existence of any sub panels). The wiring may have 2 or three wires, black, white and possibly green. If there is no green wire, the conduit becomes the safety conductor. The black wire is connected to a screw on a circuit breaker, the white wire to the white bus bar, if a green wire is used it is tied to white bus bar. Good so far?
That is the mechanics, the following is what happens. Now imagine you turn on all the breakers and appliances on the right column and turn off the rest including all the dual breakers. Current flows from the power rails to the breakers, out to the branch circuits, then gets returned on the white N wire. Then it travels to the utility transformer and goes to its earth ground, all is well and gaia smiles on you. If you now energize the right rail and its appliances and the loads are perfectly balanced, guess what happens? As the currents on the white wires from each column are equal but 180 out of phase, no current flows to the utility transformer, current is still flowing in the white wires of each branch circuit, but they are canceled at the bus bar. Again gaia is happy. Now let's talk about what really happens, there is no such thing as perfectly balanced unless you're an accountant or a flying Walenda. If all is connected and working properly a small current will be flowing back to the utility transformer on the N leg. Gaia is still happy. Now let's pretend an ambitious home owner inadvertently cuts the utility transformer ground wire while he is mowing the lawn. Remember that green wire in your sub panel? It is now going to go work. Unfortunately it is not up to the task, your feed wires are #6 or #4 and there are two of 'em. Your green wire is 12 maybe #10 it is going to become quite warm maybe even emit the magic smoke. When it finally parts, things get exciting. Not only is gaia unhappy, she is p****d . The green wires in your neighbors homes suffer the same fate. As the current in the N wire has no place to go, (remember the current rises and falls according to what is happening on each branch circuit), voltages wax and wane with devastating results. Surge protectors?? They are meant to handle millisecond transients, nothing like the swings that are taking place on your circuits. In addition the circuit breakers may see nothing amiss and not even trip.
Get the picture? Now if you have the 50 bucks, a meter and a couple of hours, I will show you how to make an equivalent circuit.
 
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