theoretical question

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Old 01-28-07, 10:51 PM
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Smile theoretical question

If the grounded conductor ( usually incorrectly reffered to as the neutral) is shorted to the grounded box (or to an ungrounded box for that matter). But first let's say to a grounded box, wouldn't the return current (now at a theoretical 0 volts with respect to the neutral/ground bar) now have a parallel path on the ground leg, thus electrifying the ground system? What prevents this from happening? I don't see how this situation blows the c/b??? Now if the box in this situation wasn't grounded, how would you ever know that this situation exists unless you were shocked by the box (providing that the shorted grounded conductor is above 0 volts). What am I not understanding here? thanx
 
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Old 01-29-07, 12:03 AM
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If the grounded conductor ( usually incorrectly reffered to as the neutral) is shorted to the grounded box (or to an ungrounded box for that matter). But first let's say to a grounded box, wouldn't the return current (now at a theoretical 0 volts with respect to the neutral/ground bar) now have a parallel path on the ground leg, thus electrifying the ground system?
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yes, but realize that the neutral is at 0 volts potential in comparison to the ground. Research why a neut is a neut and you will be surprised about using that term in a residential electrical system.
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What prevents this from happening?
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you do not make any connections between the EGC and the grounded conductor beyond the bond in the service desconnect.
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I don't see how this situation blows the c/b???
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it shouldn't. If it does, you have some problems.
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Now if the box in this situation wasn't grounded, how would you ever know that this situation exists unless you were shocked by the box (providing that the shorted grounded conductor is above 0 volts).
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the grounded conductor is at 0 volts potential to ground. As long as everything is good and connections are good, you would never know.
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What am I not understanding here?
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not sure. A neutral is at 0 volts potential to ground (or should be). You would be able to touch a neut anywhere in the system and theoretically not get shocked. Real life situations though can be different. If there is a difference in resistance from the point you are at to the panel in the two systems, you then could have a greater than 0 volts potential between the two points and recieve a shock.
 
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Old 01-29-07, 01:01 AM
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Thank-you Nap for your quick reply. I would like to continue this a little further if you have time. I've read on some archive posts from some of the "masters" that the grounded neutral conductors often have a voltage slightly higher than the theoretical (assuming all is good) o volts. My only understanding why that would be would be (like you were referring to) if the grounded n cond. were quite lenghty and were to develop a voltage drop across it (thus taking away a few volts from whatever load is on that circuit). Let's say it was a very long back to the N/G in the main, and the situation described existed (with a grounded box let's say) then the ground wire would indeed be carrying return current at say 3 volts with respect to the ground your standing on. Wouldn't this situation be like the situation in a sub-panel were the ground and neutral are not isolated, and could potentially cause the ground to become a parallel path for the neutral current (were' always warned this a big no no) Aren't the dangers here the same? this is what i'm not getting. Perhaps my theoretical scenario is why people sometimes find they get a tingle from their fixtures. Their c/b is of course not blown, so one could get shocked and killed, from what i'm reading, from a small current produced by this very small voltage. yes?? I guess there are no devices out there yet that would "sense" this condition and do something to kill the power before you get killed?? sorry about the double post
 

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Old 01-29-07, 08:38 AM
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If we're going to be clear, never say "ground conductor" or "ground wire". Say either "grounded conductor" or "grounding conductor".

Wire never has zero resistance, so current doesn't flow without a voltage drop to push it. Since the grounded conductor is a current-carrying conductor, it is never at exactly zero volts relative to the system ground as long as it is carrying current.

The grounding conductor should never carry current (except in a fault condition), so it should always be at zero volts relative to the system ground.

The grounding conductor can become a parallel conductor to the grounded conductor (always bad) whenever the connection between the two is made at more than one place in the system. That's why we allow this connection to be made in only one place.

The biggest danger from violating this rule occurs when the grounded conductor develops a fault, and thus all return current is flowing on the grounding conductor. If, sometime thereafter, the grounding conductor also develops a fault, you've just raised half the metal in your house to 120 volts.
 
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Old 01-29-07, 05:32 PM
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Thank-you John (archive man) for responding to my question and yes as wgoodrich would have it "grounded conductor"" and "grounding conductor". By the way is the abb. for grounded conductor EGC? Is there an abb. for grounding conductor? thanx Back to my original post. If the grounding conductor in a metal box is shorted (a bare portion touching the box), we now have a parallel current to the Neutral/ground bus at the main, yes?? This is assuming that the circuit in question is at the moment active of course ,and the box is properly grounded ( If so will anyone know this situation is present until one gets shocked, by say (like you said I believe) a fault in the grounded conductor (I assume this to mean a grounded conductor with the green insulation worn off and touching a metal pipe or such)? Thank you for your precious time. P.S. can anyone tell me if that master electrician wgoodrich is alive and well. Is he still sometimes active on this site?? thanx John Nelson
 
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Old 01-29-07, 08:08 PM
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"grounded conductor"" = Neutral

"Grounding conductor"= EGC

"Bonded"= The joining of metalic parts that make a conductive path to ensure electrical continuity (same potential) between all.

Just the short of it.
 
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Old 01-29-07, 09:06 PM
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Yes, EGC is the more official term for grounding conductor. It stands for Equipment Grounding Conductor.

Informally speaking, "grounded conductor" and "neutral" are used interchangeably. But they are not exactly the same thing. So to be most precise, we should use the term "grounded conductor" here and avoid the word "neutral" unless we specifically mean to imply the special circumstances of a neutral. All neutrals are grounded conductors, but not all grounded conductors are neutrals.

The question you asked cannot be answered as you asked it, because you seem to have mixed up grounding conductor and grounded conductor. Shorting the grounding conductor the the box has no effect (except for the very strange circumstances of an isolated ground circuit).

In the absense of a fault, you can screw up a lot of stuff and never suffer any consequence. Most of the electrical code is designed to ensure safety even in the event of the most common faults. It is never a good idea to assume that faults are absent. Faults do occur, and we wire to protect ourselves against as many of them as economically feasible. Some protection is judged to be cost prohibitive, and some protection is not available at any cost. Electrical work, like life, is fully of compromises.
 
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Old 01-29-07, 09:21 PM
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lectriclee_thanx for the response, but from what I'm reading in the archives and from what John Nelson just pointed out, Neutral is not the same as the grounded conductor. I'm not an electrician but I believe ,or rather it is my current understanding that the Neutral wire refers to the wire that carrries the un-balanced load of the multi-wire circuit back to the neutral bus bar, or the neutral white wire that carries the unbalanced portion of the load of L-1 and L-2 or phase 1 or phase 2, back to the center tap of the transformer.
 
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Old 01-29-07, 09:26 PM
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Just the short of it.!!!!

Never, nor do I teach engineering. (or technical writeing)
I didn't meen to Hijack, Thought maybe to give you a general thought.

John, Racraft and others are here, Your in GOOD hands.
 
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Old 01-29-07, 09:36 PM
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the grounded conductor is what is what folsk refer to as the neutral, even when it isn;t actually a neutral.
Lee is correct in his post as far as typical usage of the terms are.

Read Johns post again. He does state that a neutral is a grounded conductor but a grounded conductor is not always a neutral. e.g. the grounded conductor of a 3 phase delta system is not a neutral. The grounded conductor of a 3 phase wye system is a neutral.

More as defininition. A neutral is a neutral because of its connection on the transformer.

a grounded conductor is just that. It is attached to a grounding electrode system but it is still a current carrying conductor, as is a true neutral is also.
 
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Old 01-29-07, 10:41 PM
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W.Goodrich is alive and well. This is his website address..........

http://selfhelpforums.com/

Neutral is generally expected to carry load current whenever the loads are unbalanced between the hot legs by convention not necessarily defined as such in any book.

Neutral is a circuit conductor that may carry current in normal operation, and which is usually connected to earth. In house wiring, it is the center tap connection of the secondary winding of the power company's transformer.

In a multiphase or three-wire Edison AC system, the neutral conductor is intended to have similar voltages to each of the other circuit conductors, and similar phase spacing. By this definition, a circuit must have at least three wires for one to serve as a neutral.
In the electrical trade, the conductor of a 2-wire circuit that is connected to the supply neutral point and earth ground is also referred to as the "neutral". This is formally described in the US and Canadian electrical codes as the "identified" circuit conductor.

The NEC and Canadian electrical code only define neutral as the first of these. In North American use, the second definition is used in less formal language but not in official specifications.

The above explanation is not entirely my own but taken from one of my trade books from a few years back. I think depending on what trade you have expertise, residential, commercial, industrial or utility the term neutral has an elusive definition.

Roger
 
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Old 01-29-07, 11:25 PM
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Thank you "all" for your responses. I appreciate them all. lectriclee you can butt in any time if that's what you thought you were doing. To end my theoreticaL probing on this subject, I have just one last thing that I would like to have a naye or yaye (yes or no) answer on ,if that's possible. Here gooes. If the grounded electrode conductor (white neutral wire coming of a working light fixture in this ex.) were to touch (be in contact with) the metal box containing said wires and if that box is properly grounded (or even not properly grounded) , and if that grounded electrode conductor (n) is at the theoretical voltage of o volts or just just slightly above perhaps, will there be a zaap, bang, crack and throw the breaker like the black (hot wire would do) or would,could things go unnoticed to the homeowner? This is my final question concerning this matter. A yes or no if possible would satisfy my mental curiosity's for the present concerning this matter. Thank you all again for your time and responses. This site is a truly lovely thing.
 
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Old 01-30-07, 05:36 AM
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If the neutral wires contacts the ground wire there will not be any of what you describe. The breaker will not trip. What will happen is that the return current will split, with some on the neutral wire and some on the ground wire.
 
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Old 01-30-07, 06:36 AM
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will there be a zaap, bang, crack and throw the breaker like the black (hot wire would do)
NO

could things go unnoticed to the homeowner?
YES
 
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