What is the relationship between voltage, current, and 120V outlets in the US?

[XPTPCREWX]

no, that's not right. you couldn't be more wrong.

ha,

A/C ..."ALTERNATING CURRENT"...

 

[Redbelly98]

HENCE...

If Neutral is connected to Ground...THEN IT IS A SHORT CIRCUIT...period...

Why doesn't this trip the breaker when ground is in fact connected to the Neutral Bar?

Look at your figure from post #48.

The fact that neutral and ground are shorted together does not cause high current to flow through the fuse, because that current must still flow through the load resistance. (Fuse and load are in series.)

However, shorting hot and ground together (when neutral is already shorted to ground) would cause high current to flow through the fuse (or breaker), since then you are bypassing the load resistance in that case.

 

[XPTPCREWX]

Look at your figure from post #48.

The fact that neutral and ground are shorted together does not cause high current to flow through the fuse, because that current must still flow through the load resistance. (Fuse and load are in series.)
.

I am obviously talking to a bunch of amatures,


Neutral carries the HOT back to the DELTA/STAR configutation to complete the circuit.

NEUTRAL IS HOT.

I dare you to grab a neutral when a load is energized and touch the ground wire.

 

[MATLABdude]

HENCE...

If Neutral is connected to Ground...THEN IT IS A SHORT CIRCUIT...period...

You bet! I freaked out the first time I encountered this after tripping a breaker, because right before that, I had just accidentally made contact between the hot wire and the case in a device box (it was on a different circuit altogether, but I was still paranoid and more naive than I am now). I used the multimeter to check continuity and lo and behold, ground and the neutral wire were shorted out. After first having an "Oh S---!" moment, and then wondering how I was going to rip out all the wiring to correct this 'fault', I did some more reading and realized that yes, this was the normal state of affairs.

Why doesn't this trip the breaker when ground is in fact connected to the Neutral Bar?

As you state in a later post, yes, there is current flowing through neutral (at least, downstream of the load). But in normal operation (with a load connected and energized), the majority of the voltage drop will be in the load (hot wire connected to an ideal "source" is a small resistor, and then there's the big resistor of the load, and then there's another resistor representing the neutral). Thus, there is no tripping of the breaker (assuming your load uses less current than your breaker is rated for) because there's the load present, which controls the amount of current that flows through this loop.

Incidentally, yes, the neutral wire gets a little hotter (if that makes sense), but because the neutral wire has such a small resistance compared to the load, this is negligible, and there will not be enough potential on the neutral to drive enough current through you to hurt you were you to grab the bare neutral wire. With the assumption that load resistance is significantly (like order of magnitude) larger than wire resistance. It's still never good practice, on the chance that someone goofed on the wiring, or on the chance that you've got bad neutral wiring which throws out the assumption of the neutral being only a little "hotter" than it was with no load connected.

Now that said, consider what happens when you short live onto the case (ground). Now you've got your tiny resistance going to ground in parallel with your large resistance (the load and small resistance of the neutral wire). You'll have a short between hot and ground, and a huge amount of current through this short (constrained only by the resistance of the wiring and the case). Hopefully, your circuit breaker (on the live wire) trips and stops the current flow through both load and the short.

The exact same thing would happen if you shorted the neutral wire to the live wire. You'd bypass the load, and *really* make the neutral wire hot, and drop all your voltage across the tiny resistance represented by the wiring. And again, hopefully, your breaker trips.

 

[salman213]

Hmm, Without the livewire touching the metal case the ground wire does not create a complete circuit and as a result no current flows through it. As soon as the livewire touches the metal case for any reason, the ground wire will start to carry current.



What i am a little confused about is the purpose have the actual Earth. Why is the connection to Earth? Why not just make a complete short?

Check Image...

 

[mgb_phys]

That is said to be a 'floating' circuit and for a battery powered circuit it wouldn't matter.
But if it is floating then the + and - can be any voltage above 0 there is nothing to make the - terminal the same voltage as the Earth.
So suppose the + was at 1100V and the - was at 1000V, the circuit would work fine. But if you touched the case, even without any fault, the case would be at 1000V above ground and your feet would be connected to 0V so you would provide a path for the current to flow through!

The reason the Earth is used as a reference is that it is also the thing you are msot likely to be touching ! And you can be sure that the Earth in your house is at the same voltage as the Earth at the power station.

 

[salman213]

EDITED: I have a question about your answer now that I think about it

why wouldn't it matter if it was a DC source. ??

and if it was an AC source you said "the case would be at 1000V above ground and your feet would be connected to 0V so you would provide a path for the current to flow through!"

But since it is a "floating circuit" and not connected to the earth, wouldn't this be an OPEN CIRCUIT. If current flows through an individual where would it go?

I mean isn't that like saying

you have a -1000V--------person--------0VCurrent flows? But its not a complete circuit IS IT??

 

[XPTPCREWX]

In Engineering you MUST have a curious mind. If you dont... YOU ARE DOOMED.
The more curious the better. You need to analyze these things for yourself, because no one is going to explain them to you...simply because THEY DON'T KNOW...(as you can see in these posts.) Then you will come to a point where all your questions will look annoying to others..and you might even be hated for it...

Rememebr one thing...in Engineering you must have the "ability" VISUALIZE and expand on you visualizations, perform experiments in your head and draw your own conclusions...this is the splitting point where you leave everyone else in the dust...these abilities are not gained they are in your blood...like a talent.
look at Tesla...an absolute genius. The world hated him but all of his inventions were proven and designed in his head before on paper.

it doesn't matter in DC because DC is Direct Current...meaning that the electrons flow in a ONE WAY diection.

AC flows in both directions, like tug of war...back and forth...the neutral and hot pull electrons back and forth.

 

[XPTPCREWX]

Hmm, Without the livewire touching the metal case the ground wire does not create a complete circuit and as a result no current flows through it. As soon as the livewire touches the metal case for any reason, the ground wire will start to carry current.



What i am a little confused about is the purpose have the actual Earth. Why is the connection to Earth? Why not just make a complete short?

Check Image...

first off you drawings are wrong. and you are basing all your questions on a false basis.

ground will reduce shock/electrocution/arc blast/ and further damage to the equipment and operator, by creating a lower path of resistance and lower potential difference than anything or anyone around it.

what i think everyone need to focus on answering is HOW this is wired. Every drawing i have seen is a short circuit between HOT and NEUTRAL and GROUND.

 

[XPTPCREWX]

I know how it works, what i NEED is someone WHO KNOWS how the Neutral bar is wired...
Can someone who KNOWS please answer this?

CAN NOONE ELSE SEE WHAT WRONG WITH THIS PICTURE?
Look at the drawing and please correct it.

(this is what everyones damn picture is so far for regular operation)

 

[salman213]

This was in my text I just found it..

 

[XPTPCREWX]

Does anyone see this? seriously...

 

[isly ilwott]

I am obviously talking to a bunch of amatures,


Neutral carries the HOT back to the DELTA/STAR configutation to complete the circuit.

NEUTRAL IS HOT.

I dare you to grab a neutral when a load is energized and touch the ground wire.

At the load connection, the voltage above ground on the properly grounded neutral wire will be limited to the voltage drop caused by the current flow in the neutral. It will be a very low voltage compared to the 120volts at the load end of the hot wire.

You are not talking to "amatures". You simply misunderstand what the supposed amateurs are saying.

I'll get out my paint prushes and send you a picture that you may be able to understand.

 

[salman213]

can you post the picture u are drawing...thanks... :)

 

[XPTPCREWX]

Regardless of the voltage drop, however miniscule the voltage in neutral may be in reference to ground...the current in neutral is the same as the HOT leg supplied to the load.

Thus: neutral is HOT.

If no one understands this they are Amatures.

 

[XPTPCREWX]

With that said...

If Neutral carries the same current at the Load end of the Hot wire.

What is stopping Neutral from "equalizing" (shorting) its voltage with Ground and transferring its current into Ground?

Ground has a lower potential difference, and offers the path of least resistance.

 

[isly ilwott]

With that said...

If Neutral carries the same current at the Load end of the Hot wire.

What is stopping Neutral from "equalizing" (shorting) its voltage with Ground and transferring its current into Ground?

Ground has a lower potential difference, and offers the path of least resistance.

The neutral is grounded at the main panelboard. Any potential at the load in of the neutral wire will be due to voltage drop from one end of the neutral to the other, caused by the resistance of the neutral conductor. It will be in the range of 5 volts or less, depending on the length of the circuit. It will not be 120 volts...or anywhere near that high.

 

[mgb_phys]

why wouldn't it matter if it was a DC source. ??

I meant if it was just a small battery.
although the laws of voltage and current are the same there is an important safety difference between AC and DC. For DC to hurt you there has to be enough current flowing to actually cause burns. which since your skin is normally fairly resistive requires high voltages - like those needed for a subway train.
AC is much more dangerous because only a very small current (20-50mA) flowing through your heart is enough to kill you. Basically your heart tries to beat at the rate of the AC electricity 50/60Hz which causes a heart attack. With household AC electric at 110/220V it's easy to get such a small current through your body.

and if it was an AC source you said "the case would be at 1000V above ground and your feet would be connected to 0V so you would provide a path for the current to flow through!"

Sorry I wasn't very clear - I assumed that it was referenced to ground back at the power station.

 

[XPTPCREWX]

You are not talking to "amatures". You simply misunderstand what the supposed amateurs are saying.

I'll get out my paint prushes and send you a picture that you may be able to understand.

I think you are the one who simply misundertands.

The neutral is grounded at the main panelboard. Any potential at the load in of the neutral wire will be due to voltage drop from one end of the neutral to the other, caused by the resistance of the neutral conductor. It will be in the range of 5 volts or less, depending on the length of the circuit. It will not be 120 volts...or anywhere near that high.

who is arguing otherwise?

I am asking you...

What is stopping Neutral from "equalizing" (shorting) its voltage with Ground and transferring its current into Ground?
Ground has a lower potential difference, and offers the path of least resistance.

 

[MATLABdude]

Regardless of the voltage drop, however miniscule the voltage in neutral may be in reference to ground...the current in neutral is the same as the HOT leg supplied to the load.

Thus: neutral is HOT.

If no one understands this they are Amatures.

Ask anybody in the field (power engineers and/or electricians) and the HOT wire (slang for the LIVE wire) is the wire which carries the high potential relative to ground (amplitude-wise, as it's AC). It has nothing to do with the current it's carrying. As the voltage is what drives current through something, you're usually safe grabbing neutral wires (assuming the path from you to ground is sufficiently high resistance that you don't start looking like a convenient path to go through to get to ground).

With that said...

If Neutral carries the same current at the Load end of the Hot wire.

What is stopping Neutral from "equalizing" (shorting) its voltage with Ground and transferring its current into Ground?

Ground has a lower potential difference, and offers the path of least resistance.

Nothing, this is what happens. If you were to crack open your breaker box, you'd see that the neutral bus bar is connected to ground (at only one point, usually via a bolt--this point is code in most locales!) Since you sound like a show-me kinda guy, KILL THE MAIN BREAKER BEFORE STARTING TO REMOVE THE FRONT PANEL--NO SHORTCUTS! Or, take a look about half-way down on this page (breaker panel anatomy):
http://www.hammerzone.com/archives/elect/panel/breaker/install.htm

first off you drawings are wrong. and you are basing all your questions on a false basis.

ground will reduce shock/electrocution/arc blast/ and further damage to the equipment and operator, by creating a lower path of resistance and lower potential difference than anything or anyone around it.

what i think everyone need to focus on answering is HOW this is wired. Every drawing i have seen is a short circuit between HOT and NEUTRAL and GROUND.

Yes, there's a short between neutral and ground. I have never seen a short (i.e. non-load) between hot and these, however.

As for me, all I know is that I know nothing.

 

[salman213]

Is it possible for someone to explain why this individual gets electrocuted...(check image)..

I know MGB explained but I am still confused for some reason. I do not understand how this is a complete circuit. Can someone trace the current for me? :S

(Image: Yes that is a short no ground connection).

 

[MATLABdude]

Is it possible for someone to explain why this individual gets electrocuted...(check image)..

I know MGB explained but I am still confused for some reason. I do not understand how this is a complete circuit. Can someone trace the current for me? :S

(Image: Yes that is a short no ground connection).

In the absence of anything else (e.g. the power supply negative terminal being at higher potential than the ground the guy's standing on), the individual does not get electrocuted.

 

[salman213]

if the negative terminal is at a higher potential i still do not really understand how current would flow through the individual...

Is it NOT necessary that in AC Circuits the "End" which is the "EARTH" be connected to the negative terminal for the circuit to work..?

 

[MATLABdude]

if the negative terminal is at a higher potential i still do not really understand how current would flow through the individual...

Is it NOT necessary that in AC Circuits the "End" which is the "EARTH" be connected to the negative terminal for the circuit to work..?

But wasn't the premise of the question that the circuit was not, in fact, connected to earth? If the negative terminal of the circuit is at a different potential than ground, then this could be represented as another power supply with the hot end connected to the negative end of the first supply, and with its negative end connected to ground. Since this was not in the question, then no, the individual will not be electrocuted.

You *could* have AC circuits not connected to Earth ground. If you had a petrol generator, for instance, and you plugged a power drill into it, that power drill wouldn't be connected to Earth ground, and would still work (it'd still have the case grounding present, though this would be connected to the local ground--probably the generator casing). Assuming you sat the generator on a big, thick, sheet of something non-conductive, and you stood off of this sheet, you would have no current flow through you (and to ground) if you jammed your screwdriver into any ONE of the generator's outlet prongs. Now, if you were to jam a screw driver into one prong with one hand, and to jam another screwdriver into the other prong with your other hand, you may (literally) be playing with fire.

In most circuit diagrams, you usually see some kind of ground (or even, several types of these mixed together). These do not mean the same thing, as mentioned in another post in this thread regarding the various faces of "ground", and very often do not mean Earth ground. Except when they do (but this is usually stated somewhere).

In a large thread like this, you should make use of the QUOTE button, or MULTIQUOTE button so we can know which post you refer to.

 

[salman213]

ok..umm, thank you... I know you are trying to explain so thoroughly, but unfortunately I am still not really understanding what the answer to my question is. :(

I made a diagram, can someone complete circuit B and does current flow through the guy?


First Diagram: https://www.physicsforums.com/attachment.php?attachmentid=15144&d=1219436573

 

[Averagesupernova]

XPTPCREWX: Do a search on this forum and you will see some pix that I have posted of the inside of a breaker box. YOU are the one who is an amateur. You do not have a very good grasp on electricity in general it would seem, or at least residential AC. Incidentally, I can't recall the last time I seen so much arrogance from an individual who didn't have the story straight.

 

[XPTPCREWX]

what part of the story do I not have straight?

 

[MATLABdude]

what part of the story do I not have straight?

[TONE = Expository, not angry] Where you go against every convention I'm aware of, and call the neutral, hot? Or disregard the effect of potential relative to ground for current (where you dare us to grab the neutral on the return leg of an energized load). But these are just matters of terminology and convention, but when you're arguing armed with these, people will not understand what you mean, nor you they. Based on this and some of your other posts, you sound like you're probably a first or second year undergraduate in EE (or are higher, but non-power concentration), with some exposure to "practical" AC, but only at a high and abstracted level. So you've got a good start, but definitely haven't finished.

Take a look at this document from APC--makers of UPSs and power correction/cleaning equipment, a company that probably knows their power (Neutral Wire Facts and Myths):
http://www.apcmedia.com/salestools/SADE-5TNQYQ_R0_EN.pdf

It supports your view--neutral as a power carrier, and yet supports everybody else's view on this thread as well: neutral is hooked up to ground (as opposed to hot being hooked up to ground), and this saves you from being killed when you grab the neutral wire because you are ALSO grounded (or for better or worse, have a high resistance to ground, but are not in contact with a high current source which is at higher potential than ground).

So yes, neutral and live can be reversed and things will work. Should you grab the bare live wire? Never! Have I grabbed the bare live wire before? Yes, and I was damned lucky that I was standing on a stack of dry planks with a poor path to ground. When you are at ground potential, can you grab the bare neutral wire? Probably. Should you make a habit of it? No, because you never know when the neutral wire or load or your breaker may be broken, and your neutral has all of a sudden become an extension of hot!

...And to elaborate on my previous posting in this thread regarding neutral as it relates to ground (of the protective Earth variety), a summary of various earthing techniques (Canada and US usually have TN-C-S, and the green going to your house is PE-N, using the article terminology):
http://en.wikipedia.org/wiki/Earthing_system

 

[MATLABdude]

ok..umm, thank you... I know you are trying to explain so thoroughly, but unfortunately I am still not really understanding what the answer to my question is. :(

I made a diagram, can someone complete circuit B and does current flow through the guy?First Diagram: https://www.physicsforums.com/attachment.php?attachmentid=15144&d=1219436573

Assuming the 1000V is relative to ground (and the bottom generator of circuit B is what provides the 1000V to the top generator), the poor individual will be in parallel with the bottom generator (and implicitly, his feet are connected to the bottom terminal of the bottom generator via ground). How much current will flow through him? Depends on how much resistance he has. Hopefully, he's got on really thick rubber boots...

EDIT: I believe this is the quote you refer to:

That is said to be a 'floating' circuit and for a battery powered circuit it wouldn't matter.
But if it is floating then the + and - can be any voltage above 0 there is nothing to make the - terminal the same voltage as the Earth.

So suppose the + was at 1100V and the - was at 1000V, the circuit would work fine. But if you touched the case, even without any fault, the case would be at 1000V above ground and your feet would be connected to 0V so you would provide a path for the current to flow through!

The reason the Earth is used as a reference is that it is also the thing you are msot likely to be touching ! And you can be sure that the Earth in your house is at the same voltage as the Earth at the power station.

I hope this makes sense, but sometimes, when things have been fuzzy, I've accepted them and moved on. Only later (with more experience, or something that forced me to make use of them), did they finally make sense.

 

[MATLABdude]

One thing I don't get...

If Ground is connected to the Neutral Bar at the Breaker Box, which it is.
(in residential)...what is stopping the current of that branch circuit on the neutral side from ground out instead of returning to the source?

The Ground is being "spurred" off of the neutral bar...and providing the path of least resistance...right?

Maybe if we went back to the original post that started all of this confusion (in between the back and forth with salman213)... The situation you describe is a bit backwards, as the neutral bar is the one being spurred off the ground. Ground out is okay, from ConEd, or Ontario Hydro's points of view (or whoever it is that generates your power for you), since they get their current returned to them. It might not go through the neutral wire, but current will return to source. Might not be so okay for whatever you arc-welded to create this turn of events, but for them, that's your business (as long as you don't black out your neighborhood).

Does everything return to source? It better, otherwise you'd charge up your plot of land. Might be a good security feature against the thieves that cross from public "ground" onto your land, though, if you could somehow electrically disconnect your patch from everything around you. :-)

Possibly of interest: single-wire power transmission (but even here, a loop is formed back to source--just *literally* through the ground):
http://en.wikipedia.org/wiki/Single_wire_earth_return

 

[salman213]

Ok. Thank you, I guess that makes sense that the individual would become parallel with the "potential difference" and so current would flow through alright. THANKSSSSSSSSSSSSS this is a great thread for me. :)

 

[Hirams_bro]

XTP i understand your frustration. They don't have a clue what you're even asking. What a bunch of amateurs! I read this thread and it made me laugh; it reminded me of that movie idiocracy. If these are anything but high schoolers then this nation is doomed! How are we ever going to survive and compete with other nations? We'll be third world in less than 30 years, GUARANTEED!

What I think XTP is asking is quite simply this (I'll use an example to illustrate):

Say you have a 15A branch on a service panel. To avoid any confusion let's also say there are no other branches - "breakers" - in this panel: so just a single branch carrying 15A.
This would mean we have 15A flowing from the panel through the hot or black wire, traveling to the load and then back to the panel via the neutral wire (KCL LAW: same current going into load must come out.)

So the current is now back to the panel and has reached the neutral bus bar and here is the question: Since the neutral bus bar (in the panel) is bonded to the ground rod, why doesn't some of this current flow into the "ground rod and Earth system", in effect forming a constant short to the ground rod.

And I think I might have an answer or at least provide a helpful insight, and I hope some qualified person will correct me if I'm wrong.

QUESTION: The current does in fact short to the "ground rod and earth" constantly, but using the current divider rule, this current is negligible b/c the return to the center tap of the transformer offers a much lower resistance so that it carries the brunt of the current.

Is this right?

If so then my next question would be: what is the most important reason for the neutral being bonded to the ground?

My hypothesis:
Because the "ground rod and Earth system" by itself offers too high of a resistance (15-20 ohm) to guarantee that the circuit breaker will trip during ground fault, so it is tied to the center tap return in order to guarantee a low resistance path for the ground and thus a high enough current needed to trip the circuit breaker.

Yea...and if not then I just have to assume it's "white man's magick."

P.S. - I think the confusion resulted from people not being clear about which "Ground" was forming a hypothetical short, XTP using ground to mean what I call here "ground rod and Earth system" vs. the others taking it to mean the ground wire before it reaches the bus bar in the panel.

 

[Averagesupernova]

^^^^^^^^You have a lot to learn. Oh yeah, this thread is almost 2 years old.

 

[sophiecentaur]

@Hirams_bro
Your post makes a fair amount of sense but what is the excuse for such an abrasive introduction? A lot of the people who post here are very much "amateurs". Why is that a reason to get so shirty with them? The problem with this sort of thread is that the initial questions can all be sorted out using Kirchoff's Laws but people want 'folksy' explanations involving colloquial terms. That's because a lot of them ARE amateurs. Have a bit of patience and bite your tongue before applying the vitriol.

 

[Hirams_bro]

nova, thank you for your trenchant observation on the age of this thread. It 's good to know if I ever have any questions about dates, timezones, daylight savings, or any other time-related issues, I know just where to turn. Like you I find the whole concept of timestamps extremely atavistic and that's why I had no idea how old the thread was.

Maybe for you the forum is just an online kaffeeklatsch, but for me its about learning and helping others to learn. I think you have a lot to learn since you don't seem to have an intution about things; otherwise you might have intuited that perhaps a link to this thread was offered as an "explanation" by someone else in answer to a similar question in another thread, OR the fact that the thread hasn't been deleted yet, and maybe for good reason e.g. the admins - in their intuition - thought that it would be a good idea to leave the door open for people to contribute later, so that others in the future might benefit by finding an answer to an age-old question. Had you intuited that perhaps you might have realized why it was important for me to follow up, even on a thread as old as this.

^^^^^^^^^Age is just a number... & I'm just a good-old patriotic American like yourself!

 

[sophiecentaur]

Bearing in mind that we still discuss Darwinism, Relativity and QM (all around 100 years old), a thread of only two years' running seems quite up to date. Has anything changed since the thread was started that might make it invalid or of no interest? It seems to me that it is chock full of conceptions that need straightening out.

 

[Averagesupernova]

Hiram, I'd recommend you at least research to see the last time the user you are addressing was online when you come to a thread this old. XPT last posted June 5th of 2009. It's pretty unlikely XPT will ever see anyting directed his way by you.