Circuit completion : is it necessary?

  • Thread starter AlchemistK
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In summary: In your example, one of the terminals of the battery (most likely the negative) was (edit: probably) fastened to the chassis framework of the car to use it as an intentional return path back to the source (the battery). It found it's way back to the battery through the metal parts of the car... It didn't drain itself into the ground through the tires, I assure you.
  • #71
rcgldr said:
In most places in the USA, the neutral wire is center tapped from the last step down transformer, and it's not grounded directly, but is supposed to be within 10 volts of Earth ground due to grounding at previous transformer stages. In my home I see .3 to .5 volts between "netrual" and the actual grounded 3rd pin on the 110 volt outlets in my home.

According to this picture at hyperphysics:

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/imgele/gfault.gif

the neutral wire is grounded at the centertap, and to the same "neutral tie block" as the ground wire.

I agree that it makes no sense. We've already established that 10V is not dangerous (touching the terminals of a car battery), so why not just connect the ground wire to the neutral wire instead of driving a pin into the ground to connect to the ground wire? Can't you just connect the ground wire to the neutral wire instead?
 
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  • #72
I agree that it makes no sense. We've already established that 10V is not dangerous (touching the terminals of a car battery), so why not just connect the ground wire to the neutral wire instead of driving a pin into the ground to connect to the ground wire? Can't you just connect the ground wire to the neutral wire instead?

The mains power lines that provide power for homes and business runs on AC electricity. The two lines that run into your house are both the positive AND negative lines at the same time. When the AC cycle is at one phase one line is + and the other -, and when the cycle reverses so do the lines. The ground is simply there for any accidents so that the current will flow to ground instead of through your toaster and into you.
 
  • #73
sophiecentaur said:
It's all a matter of Capacity.
Imagine the battery and bulb connected by a large capacitor in series. You would have a series RC circuit. At switch on, you would find that current would flow (lighting the bulb a bit) until the Capacitor was charged. Leaving out the huge Capacitor gives you a minute capacitor (the gap between the two wire ends). Only a minute current will flow for a very short time.

The capacitor would never charge unless the battery was connected at both terminals. The chemical reaction that takes place to provide electrons cannot occur if only one terminal is connected. There is NOT a charge imbalance on either terminal of a battery. The cells that make up a battery are connected by something that let's charges flow between the half cells, so that when the reactions on the anode and cathode take place the removed charges can be replaced, avoiding a difference in charge that would stop any further reactions. THAT is why you will not have leakage from one terminal to ground or to anywhere else. That would cause an imbalance in charges, as either the anode or cathode isn't reacting and taking or replacing charges in the electrolyte.
 
  • #74
AlchemistK said:
Can the power supply in our house also be treated like a battery?
Then we shouldn't get a shock if we put one finger in the live wire socket until we put another finger in the neutral wire socket?
you don't get much of a shock unless you're connected to ground well enough. but yes.
Actually that is used sometimes when working on equipment in the lab / doing repairs. Isolation transformer. Then you don't really have live and neutral.
The problem is that when you try it for entire house, eventually some device is going to connect either wire to the ground due to a fault, or worse yet, some device is going to leak high voltage into it, raising both lines to very high voltage + the line voltage, which is going to damage the insulation somewhere. Also, in case of lightning strike. Or if the transformer that steps down several kv to the line voltage for the house fails, developing connection between the several kv part and the 240v (120v if you are in US) part.
In those cases, if the neutral is grounded, the current from overvoltage on live would go through the winding in the transformer onto neutral.
 
  • #75
@DRAKKITH
My RC idea assumed that the circuit was complete, of course. That was just an extreme example to establish the principle. The fact is that whenever you connect a wire to one end of a battery there will be some small charge flow; some extra electrons will move from one end to the other until the Potential is at a minimum again. The amount of charge that will actually flow is determined by the Capacity that is introduced across the battery terminals.
 
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  • #76
RedX said:
According to this picture at hyperphysics:

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/imgele/gfault.gif

the neutral wire is grounded at the centertap, and to the same "neutral tie block" as the ground wire. I agree that it makes no sense. We've already established that 10V is not dangerous (touching the terminals of a car battery), so why not just connect the ground wire to the neutral wire instead of driving a pin into the ground to connect to the ground wire? Can't you just connect the ground wire to the neutral wire instead?
Apparently some of the current flows back through the neutral and its Earth ground points (in addition to the breaker panel, also in transmission transformers). What I don't get is if current is flowing back through the neutral and Earth ground, and if the ground wires are also tapped into the earth, then why is there a neutral to ground voltage of up to 10 volts when measured at an outlet, and also why are the "neutral" wires insulated, while the ground wires are bare copper wires?
 
  • #77
AlchemistK said:
Can the power supply in our house also be treated like a battery?
Then we shouldn't get a shock if we put one finger in the live wire socket until we put another finger in the neutral wire socket?

AC voltages, if we ignore induction, radiation, capacitive coupling, etc., will behave exactly the same way as this battery we've been talking about. If you "freeze" any instant in time, we can analyze it in the exact same way as we do a battery... The difference is that the voltage potential is constantly changing magnitude and polarity, so to discuss it in terms of a circuit you need to kind of "freeze" it first. But it behaves the same way

And you need to be careful about sticking your finger in the live wire socket because in residential power distribution, we "ground" the neutral wire... this means that the ground you are standing on is already connected to the neutral wire back at the box. But what you're thinking is exactly correct. If we didn't "ground" the neutral back at your service entrance, you could stand there and hold on to the live wire all day standing in a puddle barefoot and you would not get shocked. The only reason current will travel through you at your house (and the reason you should NOT do this) is because they intentionally connected the neutral to the ground. You would complete the circuit back to the source through the ground because they set it up that way.

All that being said... I've done this myself and nothing happens. The resistance of your body and the ground is so high that it is essentially an open. I don't recommend doing it just because you never know how resistive your body is and how close you are to the ground rod... plus if you're dealing with higher voltages, this could be extremely dangerous. My experience was with 120V. Too many variables, so nobody should be doing it. You could kill yourself so don't try it!


RedX said:
The power supply can continuously push current through you. The battery won't push more current through you until you can get rid of the charges on the other lead of the battery.

both sources would continue to push current through you... this is ohm's law. it comes down to the available voltage and it's ability to "push" the current through the high resistance of your body. The battery, however, would drain very quickly compared to the AC power source at your house.

RedX said:
My guess is you'll probably die if you stick your finger in the live wire socket, although I'm not completely sure since if the socket has a ground fault interrupter, wouldn't it trip?

Also, what would happen if the neutral wire weren't grounded/earthed? Then would you die if you touch the neutral wire? What if the neutral wire were only connected to the transformer and there was no connection between the neutral wire and the ground?

If we didn't ground anything, then you could touch the neutral all day without danger. You caould also touch the "hot" or "live wire" all day without any danger. You aren't completing the circuit. As I explained above... the only danger we have messing around with power lines at our house is due to the fact that we intentionally "ground" the neutral wire at just about every power pole (in the US anyway) in the country and again at every service entrance to every house. There is a good reason for this that could take up an entire new thread, but for the sake of this conversation, the ground is completing the circuit (EDIT FOR CLARIFICATION: when you touch a powerline at your house, not under normal operating conditions) because the power company intentionally designed the distribution system that way.
 
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  • #78
sophiecentaur said:
@DRAKKITH
My RC idea assumed that the circuit was complete, of course. That was just an extreme example to establish the principle. The fact is that whenever you connect a wire to one end of a battery there will be some small charge flow; some extra electrons will move from one end to the other until the Potential is at a minimum again. The amount of charge that will actually flow is determined by the Capacity that is introduced across the battery terminals.

And where did that extra charge come from?
I quote from Dalespam, post 3.

AlchemistK, I think you may have a misconception about how batteries work. Batteries are electrically neutral, they do not have a "higher charge relative to the bulb". What they have is a potential difference between the terminals. If you touch only one end of the bulb to one of the battery terminals then you have not put the potential difference across the bulb, so no current.

Both terminals of a battery are neutral with respect to everything else. Inside the battery there are chemicals that want to react with each other. However, without a way for electrons to flow from one electrode to another, those reactions cannot take place, as it would result in a difference in potential inside the battery.

This is not like a capacitor. You don't have a buildup of charge on one side and a depletion on the other. And quite frankly, if you are saying that an absolutely miniscule amount of charge builds up, such as like 3 electrons, come on...ignore it and move on. That most definitely does NOT have any noticeable effect on any of the examples here. I'm sure i can get a difference in charge just by touching my glass of milk, but that doesn't mean that me and my milk act like a capacitor or battery or anything. The answer to the OP's original post is still "No, the bulb wouldn't glow."
 
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  • #79
Evil Bunny said:
If we didn't ground anything, then you could touch the neutral all day without danger. You caould also touch the "hot" or "live wire" all day without any danger. You aren't completing the circuit.

would the result vary if DC current is used?
 
  • #80
Dmytry said:
For example, you can put battery on insulated table, and then put electrostatic charge on it (using plastic bag for example). That won't change the charges stored inside battery, you won't really charge the battery in the sense in which the battery charger does. However, this way you can make potentials on the leads be e.g. 10 000 v and 10 012 v (to ground). Then if you connect one to ground, current will flow for a short time. It's really same as if you had piece of metal in place of battery, you can put charge on it, you can get charge off it, etc. It's very confusing to put net charge onto battery lol.

You need to distinguish between two equal opposite charges 'stored' inside the battery, and the net charge of the battery.

Talk about confusion! Now we're injecting static electricity into the mix and trying to discuss it alongside the basic circuit theory of a 12V battery as a voltage source... Why make this so much more complicated than it is? Maybe I'm wrong, but I find it extremely hard to believe that the OP was referring to a static discharge off the battery that is unrelated to the voltage potential between it's posts.

Here is a question that I think is related to this discussion... Let's ignore static electricity and talk about only the voltage potential from the battery:

If we connected a copper rod (let's say 3cm diameter and 1 meter long) on it's end to the negative pole of a 12 V battery that was sitting on a well insulated platform and we encapsulated the positive pole of the battery (in an effort to rid ourselves of any stray capacitance), would electrons "rush" up to the tip of that rod to "equalize" the charges of the negative pole and the copper rod?
 
  • #81
Evil Bunny said:
If we connected a copper rod (let's say 3cm diameter and 1 meter long) on it's end to the negative pole of a 12 V battery that was sitting on a well insulated platform and we encapsulated the positive pole of the battery (in an effort to rid ourselves of any stray capacitance), would electrons "rush" up to the tip of that rod to "equalize" the charges of the negative pole and the copper rod?


From what i know about conduction of charges, yes.

http://www.physicsclassroom.com/class/estatics/u8l2c1.gif
 
  • #82
If we didn't ground anything, then you could touch the neutral all day without danger. You caould also touch the "hot" or "live wire" all day without any danger. You aren't completing the circuit. As I explained above... the only danger we have messing around with power lines at our house is due to the fact that we intentionally "ground" the neutral wire at just about every power pole (in the US anyway) in the country and again at every service entrance to every house. There is a good reason for this that could take up an entire new thread, but for the sake of this conversation, the ground is completing the circuit because the power company intentionally designed the distribution system that way.

I don't think all of this is correct. The neutral wire is also a conductor. I have put my finger in an outlet as a child and most definitely know it shocked me. Touching either of the conductor wires, IE the hot or neutral wires, can result in being shocked as far as I know.

Also, the ground wire has nothing to do with completing the circuit. From wikipedia:

Ground or Earth in a mains (AC power) electrical wiring system is a conductor that provides a low impedance path to the Earth to prevent hazardous voltages from appearing on equipment (the terms "ground" (North American practice) and "earth" (most other English-speaking countries) are used synonymously here). Normally a grounding conductor does not carry current.

Neutral is a circuit conductor (that carries current in normal operation), which is connected to Earth (or ground) generally at the service panel with the main disconnecting switch or breaker.

To go back to the bird on a power line example, the reason the birds don't get shocked is because there is nowhere for the current to flow if it tries to go through the bird. The line is the same potential effectively everywhere (on the scale of a bird sized length of cable), and since there is nowhere for the current to go except through the line the bird is safe. Now, if the bird touches a hanging line, that's a different story that might involve toasted bird...as most likely you have two different potential lines connected by a bird.
 
  • #83
Evil Bunny said:
Talk about confusion! Now we're injecting static electricity into the mix and trying to discuss it alongside the basic circuit theory of a 12V battery as a voltage source... Why make this so much more complicated than it is? Maybe I'm wrong, but I find it extremely hard to believe that the OP was referring to a static discharge off the battery that is unrelated to the voltage potential between it's posts.

Here is a question that I think is related to this discussion... Let's ignore static electricity and talk about only the voltage potential from the battery:

If we connected a copper rod (let's say 3cm diameter and 1 meter long) on it's end to the negative pole of a 12 V battery that was sitting on a well insulated platform and we encapsulated the positive pole of the battery (in an effort to rid ourselves of any stray capacitance), would electrons "rush" up to the tip of that rod to "equalize" the charges of the negative pole and the copper rod?

My impression is that OP is trying to unify his knowledge of electrostatics and charges with his knowledge of basic circuitry (batteries etc). That is a perfectly reasonable thing to do. Yes that is a little bit complicated and confusing, but that is what OP is confused about and that's what he wants clarified, not basic circuitry with perfect batteries.

Here, basic circuitry is not considered any more or less advanced than basic electrostatics, albeit the textbooks can often neglect to explain the relation between two, leading to the confusion like that of OP.
 
  • #84
RedX said:
the neutral wire is grounded at the centertap, and to the same "neutral tie block" as the ground wire.

I agree that it makes no sense. We've already established that 10V is not dangerous (touching the terminals of a car battery), so why not just connect the ground wire to the neutral wire instead of driving a pin into the ground to connect to the ground wire? Can't you just connect the ground wire to the neutral wire instead?

The neutral is the path back to the source (transformer).
The "ground wire" is not meant to carry any current under normal conditions. It is there to give a low resistance path back to the source in the event of a fault. If the "hot" wire of your stove became disconnected and touched the metal framework of the stove, then you came along and touched it, you would receive a shock (because the system is grounded). This "ground wire" (a horrible choice of names that causes confustion) is used to bond all the metal parts in your house together and send the current back to the source on a big fat low resistance copper wire instead of through you. The hope is that this low resistance path back to the source would open an overcurrent protection device and turn that circuit off.

The National Electric Code requires that you connect this "ground" and the "neutral" together at the service entrance and not at every connection point in the house. The reason you measure a small voltage between ground and neutral is because of voltage drop on the wire.
 
  • #86
If we connected a copper rod (let's say 3cm diameter and 1 meter long) on it's end to the negative pole of a 12 V battery that was sitting on a well insulated platform and we encapsulated the positive pole of the battery (in an effort to rid ourselves of any stray capacitance), would electrons "rush" up to the tip of that rod to "equalize" the charges of the negative pole and the copper rod?

No. There is no difference in potential or charges.
 
  • #87
Alright...i see.

So the bulb should light in the above case if instead of a battery, a negatively charged body is used?

To finish off your original questions, YES. If you connected a source of negatively charged particles to your light bulb, they would discharge into your circuit and light bulb until the charges equalized. Would this light up the bulb? Depends on the amount of current you had flowing and such.

The difference between this and the battery is that a battery is NOT a source of extra built up charges. Static electricity is however. An extreme example of this is Lightning. If lightning struck one terminal of your bulb you can bet your singed face that the bulb "lit up". (And more)
 
  • #88
Drakkith said:
I don't think all of this is correct. The neutral wire is also a conductor. I have put my finger in an outlet as a child and most definitely know it shocked me. Touching either of the conductor wires, IE the hot or neutral wires, can result in being shocked as far as I know.

Also, the ground wire has nothing to do with completing the circuit. From wikipedia:

You were most likely shocked because you got your finger across both terminals, but like I said.. there are a lot of variables and the possibility exists. I've done it as an adult and got nothing off of either post individually and gotten a shock when I got across them...

Anyway, the only way one would get shocked by touching only one of the terminals is if the current traveled through you and went through the ground to find it's way back to the source.

To be clear... I know the ground wire has nothing to do with completing the circuit under normal conditions. It's there to complete the circuit only if something goes wrong. If that point didn't come through in my explanations, I apologize because it is an important one.
 
  • #89
So the only problem is that a battery requires electrons to return back to the other terminal to show any significant movement of charges.
Any voltage source that does not show this property?
 
  • #90
Evil Bunny said:
If we connected a copper rod (let's say 3cm diameter and 1 meter long) on it's end to the negative pole of a 12 V battery that was sitting on a well insulated platform and we encapsulated the positive pole of the battery (in an effort to rid ourselves of any stray capacitance), would electrons "rush" up to the tip of that rod to "equalize" the charges of the negative pole and the copper rod?

Drakkith said:
No. There is no difference in potential or charges.

OK thank you. This is the point I have been trying to make throughout this entire thread and it is being met with great resistance.

I believe (but I'm not certain) that this gets to the bottom of what the OP was asking...
 
  • #91
AlchemistK said:
So the only problem is that a battery requires electrons to return back to the other terminal to show any significant movement of charges.
Any voltage source that does not show this property?

No. All voltage sources require a return.
 
  • #92
voltage sources

Have a care with the use of this term.

I think you mean a general device which supplies electrical energy.

However the term voltage source has a much narrower and more precisely defined meaning in circuit theory.

Incidentally much confusion arises when special definitions from circuit theory are introduced into a discussion about physics and vice versa.

Circuit theory is much more specialised and limited than Physics and in particular makes certain assumptions for ease of analysis and calculation, that are not realisable in the real world .
 
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  • #93
Ahh, and to actually answer the question.
Evil Bunny said:
Here is a question that I think is related to this discussion... Let's ignore static electricity and talk about only the voltage potential from the battery:
Did you ever understand how 'battery electricity' relates to 'static electricity' ?
If we connected a copper rod (let's say 3cm diameter and 1 meter long) on it's end to the negative pole of a 12 V battery that was sitting on a well insulated platform and we encapsulated the positive pole of the battery (in an effort to rid ourselves of any stray capacitance), would electrons "rush" up to the tip of that rod to "equalize" the charges of the negative pole and the copper rod?
that is depend to which potential the negative pole was at, what potential the rod was at, and what stray capacitance both the positive and the negative pole have vs the rod and the ground. The charge that would flow equals to capacitance between the rod and both of the battery poles, multiplied by the difference in potentials. If the capacitance is zero, the charge will be zero.

The OP is clearly trying to find a relation between his knowledge of 'static electricity' and 'battery electricity', into some sort of unified understanding. Assuming that parasitic capacitances are zero does not permit unified understanding.

The situation is such that e.g. 2 A*h battery has a charge of 7 200 Coulomb stored chemically inside.
The stray capacitance of, say, 1pF at potential difference of 12v stores 0.00 000 000 012 Coulombs.

That is why it is very common to neglect stray capacitances when discussing batteries.

edit: whoops mixed up mAh vs Ah
 
  • #94
Dmytry said:
that is depend to which potential the negative pole was at,

with respect to what?

Dmytry said:
what potential the rod was at,

with respect to what?

You keep talking about potential as if you can have it at one point. You can't. Potential at one point is with respect to another point... In this case we're talking about the potential between the rod and the negative pole. This potential is ZERO VOLTS in this case. No current flowed. No light bulb lit.

Dmytry said:
and what stray capacitance both the positive and the negative pole have vs the rod and the ground. The charge that would flow equals to capacitance between the rod and both of the battery poles, multiplied by the difference in potentials. If the capacitance is zero, the charge will be zero.

The ground is irrelevant. we're on an insulated platform. The positive pole of the battery is irrelevant. we encapsulated it.

You're trying to invent capacitance where it doesn't exist.

The answer to the question in post #1 is the bulb absolutely will not light. No way it can. This stray capacitance that may or may not exist will in no way provide enough current for any glow to occur.
 
  • #95
Evil Bunny said:
You keep talking about potential as if you can have it at one point.

Potential is taken at one point, its the potential difference which is relative.

The electric potential at a point in an electric field is defined as the work done in moving a unit charge from infinity to that point.
 
  • #96
This thread has bi-polar disorder, I think. On the one hand we have the transformer / live/ neutral discussion and, on the other hand, we have the connect a battery and what happens discussion. Whilst it's all 'Electricity', they two ideas are interfering with each other. It's OK for someone who knows about these things but, for someone fresh, it makes things much harder than necessary.

The power engineering discussion is made complicated by the fact that the neutral we all know and love in the UK is fairly different from the Neutral that goes into many US homes. Essentially, the Neutral which a three phase distribution system takes very little current, when the three phases are loaded equally. This keeps the Neutral volts pretty near Earth all the time. The Neutral that goes into the US home, as I understand, comes from a local transformer which is centre tapped to give both a 110V and 220V supply. It is, inherently, not balanced and, depending on the lopsidedness of a typical domestic load during the day, you could expect some much higher volts on a Neutral. You really don't want lots of Earth currents sloshing around your domestic pipes and steel frames as it can cause embarrassing Hum, for a start. Current in the Neutral cable runs right next to the Live current and there is much less magnetic field generated. So - using the Neutral for return makes sense - else, why not have a single line supply to the home and rely on Earth as a return? Think of the copper you'd save!
 
  • #97
Evil Bunny said:
with respect to what?
with respect to what?

You keep talking about potential as if you can have it at one point. You can't. Potential at one point is with respect to another point... In this case we're talking about the potential between the rod and the negative pole. This potential is ZERO VOLTS in this case. No current flowed. No light bulb lit.
1: Check electric potential on wiki.
http://en.wikipedia.org/wiki/Electric_potential
2: I was speaking of difference of potentials. Not a single result depended on the absolute potential (which i suppose is defined as energy of unit charge brought in from far outer space)
The ground is irrelevant. we're on an insulated platform. The positive pole of the battery is irrelevant. we encapsulated it.
how do you encapsulate something to totally eliminate the capacitance?
I'd really love to know, because i am building some electronic circuit where I have to calculate capacitance of every piece of wire.
You're trying to invent capacitance where it doesn't exist.

The answer to the question in post #1 is the bulb absolutely will not light. No way it can. This stray capacitance that may or may not exist will in no way provide enough current for any glow to occur.
I told already that an incandescent lightbulb won't light up, but if the voltage is, say, 200v, and if it is a neon lamp, and if capacitances are realistic, it will lit up briefly and visibly (in a dark room).
 
  • #98
Dmytry said:
1:
how do you encapsulate something to totally eliminate the capacitance?
I'd really love to know, because i am building some electronic circuit where I have to calculate capacitance of every piece of wire.

Exactly. And every piece of wire you hang on the battery will acquire a small charge. It's hard to reduce stray capacitance to less than one or two pF.

I find it bizarre that we are discussing picoCoulombs on the one hand and Mains supply currents on the other.
 
  • #99
Evil Bunny said:
If we didn't ground anything, then you could touch the neutral all day without danger. You caould also touch the "hot" or "live wire" all day without any danger. You aren't completing the circuit. As I explained above... the only danger we have messing around with power lines at our house is due to the fact that we intentionally "ground" the neutral wire at just about every power pole (in the US anyway) in the country and again at every service entrance to every house. There is a good reason for this that could take up an entire new thread, but for the sake of this conversation, the ground is completing the circuit (EDIT FOR CLARIFICATION: when you touch a powerline at your house, not under normal operating conditions) because the power company intentionally designed the distribution system that way.

I'm not sure about this. If the neutral wire weren't grounded, I think you would still get shocked if you simultaneously touched the neutral wire (or the hot wire) and a piece of metal plumbing that goes to the ground. But because the neutral wire is grounded, you can touch the neutral wire and a piece of plumbing and be fine. You seem to be saying that if the neutral wire weren't grounded, then the only way to get shocked is to touch the hot wire and the neutral wire at the same time (you could touch the hot or neutral wire [but not both] and the plumbing at the same time and have no fear), which is consistent with your one-terminal battery connection position, but I don't think that's right.

Also when you say you can't get shocked by touching just the hot wire, I'm doubtful about that too. I understand there is a lot of resistance between you and the ground, but I hear a lot of warnings about not sticking your finger in the socket. The current would have to travel through you, through the floor, and through metal piping which sounds like a lot of resistance, but it only takes a little current to kill you.
 
  • #100
rcgldr said:
Apparently some of the current flows back through the neutral and its Earth ground points (in addition to the breaker panel, also in transmission transformers). What I don't get is if current is flowing back through the neutral and Earth ground, and if the ground wires are also tapped into the earth, then why is there a neutral to ground voltage of up to 10 volts when measured at an outlet, and also why are the "neutral" wires insulated, while the ground wires are bare copper wires?

I have no idea why neutral wires are insulated. If anything only the hot wires need to be insulated.

The fact there is 10 volts between the neutral and ground suggests that maybe you are right and neutral only connects to the center tap, where it has been reduced to 10V with respect to the ground by previous transformers. But according to hyperphysics, the neutral and ground wire are physically tied together at a location and driven into the ground before the center-tap location.

I don't understand why a third prong is needed for ground. Can't you just plug the chassis of an appliance directly to neutral? Or is that what is done? Because I notice some appliances only have two prongs. Does this mean the chassis of the appliance shares the same connection to neutral as the appliance itself, i.e. two wires connect to the neutral prong?
 
  • #101
RedX said:
I don't understand why a third prong is needed for ground. Can't you just plug the chassis of an appliance directly to neutral? Or is that what is done? Because I notice some appliances only have two prongs. Does this mean the chassis of the appliance shares the same connection to neutral as the appliance itself, i.e. two wires connect to the neutral prong?

This, as I have already said, is because the neutral is a three phase invention. Letting it float is good for keeping the transmissions on each of the three phases balanced. Anybody disagree with that?
Three phase generation is a great invention but it does generate a lot of conceptual problems.
 
  • #102
RedX said:
You seem to be saying that if the neutral wire weren't grounded, then the only way to get shocked is to touch the hot wire and the neutral wire at the same time (you could touch the hot or neutral wire [but not both] and the plumbing at the same time and have no fear), which is consistent with your one-terminal battery connection position, but I don't think that's right.

Ok... let's simplify the circuit.

You have a battery and a resistor. You connect one end of the resistor to one terminal of the battery. Does anything happen? No. No complete circuit. No current flow.

Now replace the battery with an AC source. No grounds, no plumbing, nothing but an AC source with two terminals. Now... connect one end of that same resistor to only one terminal of the AC source. Does anything happen? No. No complete circuit. No current flow.

Now replace the resistor with yourself... see my point now?

Introducing "ground" into the conversation complicates things and confuses people...


RedX said:
I have no idea why neutral wires are insulated. If anything only the hot wires need to be insulated.

They carry just as much current as the hot wires in the branch circuits of your house under normal operating conditions.

RedX said:
The fact there is 10 volts between the neutral and ground suggests that maybe you are right and neutral only connects to the center tap, where it has been reduced to 10V with respect to the ground by previous transformers. But according to hyperphysics, the neutral and ground wire are physically tied together at a location and driven into the ground before the center-tap location.

The neutral is connected to the center tap. It's also connected to a ground rod at your service entrance and at the utility pole. Again... the reason you measure a small voltage between the "ground wire" and the neutral in your house is because of voltage drop. You are only allowed to connect the neutral and the "ground wire" together at the service entrance. You are not allowed to connect them together anywhere else in your house (per the NEC in the US). The further away from the service entrance you get, the greater the voltage reading will be between neutral and the "ground wire".

RedX said:
I don't understand why a third prong is needed for ground...

For safety reasons.. In the US there never used to be a 3rd prong and everything worked just fine, except that under fault conditions metal appliances had voltage present with respect to ground and it was potentially dangerous.

They added a "ground wire" (third prong) that bonded all the metal things in your house together and tied it together with the neutral (at the service entrance) to create a parallel path back to the source. The reason they did this was in case of a fault, this current would travel back along the low resistance "ground wire" back to the source instead of through your body. If you simply tied everything to the neutral, then under "normal conditions" you would have current flowing through the neutral AND through all of the metal things in your house. This is not a desirable situation.
 
  • #103
sophiecentaur said:
This, as I have already said, is because the neutral is a three phase invention. Letting it float is good for keeping the transmissions on each of the three phases balanced. Anybody disagree with that?

Yes I do... I will try to explain further later... no time right now... I just touched on it a little bit in my previous post
 
  • #104
If the neutral were allowed to float anywhere and a low resistance load applied to one of the phases then the volts on the other two phases could end up as 400V instead of 240V. That would not be good. Why does no one else consider the three phase thing in this discussion? There is no major system of electricity generation that does not use three phases so it is a major consideration.
 
  • #105
sophiecentaur said:
If the neutral were allowed to float anywhere and a low resistance load applied to one of the phases then the volts on the other two phases could end up as 400V instead of 240V. That would not be good. Why does no one else consider the three phase thing in this discussion?

Most houses (if not all) in the US are wired with single phase. Yes, it originates as three phase (upstream) but we're only using one of the phases. This third prong on the plug receptacles that people are calling the "ground wire" (whose technical term is an "equipment grounding conductor") has absolutely nothing to do with the neutral whatsoever. It is used for bonding the metal parts in your house.
 
<h2>1. Is circuit completion necessary for a circuit to function?</h2><p>Yes, circuit completion is necessary for a circuit to function properly. Without a complete circuit, electricity cannot flow and the circuit will not work.</p><h2>2. What happens if a circuit is not completed?</h2><p>If a circuit is not completed, electricity will not flow and the circuit will not work. This can result in a device or system not functioning properly or at all.</p><h2>3. How can I tell if a circuit is complete?</h2><p>You can tell if a circuit is complete by using a multimeter to measure the voltage and resistance of the circuit. If there is a complete path for electricity to flow, the multimeter will show a reading. You can also visually inspect the circuit for any breaks or disconnected components.</p><h2>4. Can a circuit be completed in different ways?</h2><p>Yes, there are different ways to complete a circuit. For example, a series circuit is completed when electricity flows through each component in a single path, while a parallel circuit is completed when electricity flows through multiple paths. Additionally, circuits can be completed using different materials such as wires, conductive metals, or even water.</p><h2>5. Why is circuit completion important in electronics?</h2><p>Circuit completion is important in electronics because it allows for the flow of electricity and enables devices to function. Without a complete circuit, electricity cannot flow and devices will not work. Additionally, understanding circuit completion is essential for troubleshooting and repairing electronic devices.</p>

1. Is circuit completion necessary for a circuit to function?

Yes, circuit completion is necessary for a circuit to function properly. Without a complete circuit, electricity cannot flow and the circuit will not work.

2. What happens if a circuit is not completed?

If a circuit is not completed, electricity will not flow and the circuit will not work. This can result in a device or system not functioning properly or at all.

3. How can I tell if a circuit is complete?

You can tell if a circuit is complete by using a multimeter to measure the voltage and resistance of the circuit. If there is a complete path for electricity to flow, the multimeter will show a reading. You can also visually inspect the circuit for any breaks or disconnected components.

4. Can a circuit be completed in different ways?

Yes, there are different ways to complete a circuit. For example, a series circuit is completed when electricity flows through each component in a single path, while a parallel circuit is completed when electricity flows through multiple paths. Additionally, circuits can be completed using different materials such as wires, conductive metals, or even water.

5. Why is circuit completion important in electronics?

Circuit completion is important in electronics because it allows for the flow of electricity and enables devices to function. Without a complete circuit, electricity cannot flow and devices will not work. Additionally, understanding circuit completion is essential for troubleshooting and repairing electronic devices.

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