Grounded Conductor/Neutral

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tom baker

First Chief Moderator
Staff member
Some advice on this, down to the last week for me to make a proposal.

The NEC added a definition of neutral in the 2008. In some cases a neutral is a grounded conductor and in some cases its not. Its not obvious how a neutral becomes a grounded conductor. A direct link needs to be made, much as the 2008 made the link on how to size the GEC in 250.24 (D)

Something like: "the neutral conductor becomes a grounded conductor when the neutral point is grounded per to 250.20"

I see now why the term grounded conductor was left in the NEC instead of replacing it with neutral. But most of the time that white wire is a neutral.
 

dnem

Senior Member
Some advice on this, down to the last week for me to make a proposal.

The NEC added a definition of neutral in the 2008. In some cases a neutral is a grounded conductor and in some cases its not. Its not obvious how a neutral becomes a grounded conductor. A direct link needs to be made, much as the 2008 made the link on how to size the GEC in 250.24 (D)

Something like: "the neutral conductor becomes a grounded conductor when the neutral point is grounded per to 250.20"

I see now why the term grounded conductor was left in the NEC instead of replacing it with neutral. But most of the time that white wire is a neutral.
"In some cases a neutral is a grounded conductor and in some cases its not."
You didn't quite get that right. . On 50 to 1000 volt systems, the neutral is always required to be grounded [see 250.20(B)(2)+(3)].

What you might have meant to say is:
In some cases a grounded conductor is a neutral and in some cases its not.
Or in other words: the neutral is always grounded but the grounded is not always a neutral. . You can corner ground a 3 phase delta transformer and the grounded conductor is not a neutral, it is a phase.

Neutral is a more narrowly defined smaller category.
Grounded is a broader larger defined category.

"most of the time that white wire is a neutral."
But a corner grounded phase conductor is also white [or gray].
White signifies grounded. . It does not signify neutral.
 

resistance

Senior Member
Some advice on this, down to the last week for me to make a proposal.

The NEC added a definition of neutral in the 2008. In some cases a neutral is a grounded conductor and in some cases its not. Its not obvious how a neutral becomes a grounded conductor. A direct link needs to be made, much as the 2008 made the link on how to size the GEC in 250.24 (D)

Something like: "the neutral conductor becomes a grounded conductor when the neutral point is grounded per to 250.20"

I see now why the term grounded conductor was left in the NEC instead of replacing it with neutral. But most of the time that white wire is a neutral.
I'm on board!
 

tom baker

First Chief Moderator
Staff member
I would make a proposal but I am not sure where it should go. Its not obvious when a neutral is a grounded conductor. For most electricians a white wire is a neutral.
Perhaps a change to the scope of Article 200.

Point out the issues and let the CMP wrestle with it and pick it up as a comment.
 

Lcdrwalker

Senior Member
I think that Charlie said it best in another thread when he said that the neutral is always the grounded conducto but the grounded conductor isn't always the neutral conductor.

Maybe someone should submit a proposal to require a certain color for the grounded conductor in a corner grounded delta system as the high leg of a center grounded delta is required.

This would mean that only the "grounded conductor/neutral" would be white or gray.
 

TOOL_5150

Senior Member
You can corner ground a 3 phase delta transformer and the grounded conductor is not a neutral, it is a phase.
"the neutral is always grounded but the grounded is not always a neutral" makes sence to me, but I dont quite understand WHY a grounded is not always a neutral. I have little experience with 3phase, so please excuse my ignorance. Why would you want to ground a phase?

~Matt
 

Lcdrwalker

Senior Member
A corner grounded three phase system is only used in a limited amount and restricted to phase to phase loads or three phase loads. Since this type of service only requires two transformers, it is cheaper for the POCO to put in. This also qualifies as a second service when a single phase service already exists.
 

George Stolz

Moderator
Staff member
"the neutral is always grounded but the grounded is not always a neutral" makes sence to me, but I dont quite understand WHY a grounded is not always a neutral. I have little experience with 3phase, so please excuse my ignorance. Why would you want to ground a phase?

~Matt
In a residential 1? 120/240 system, if you have two ungrounded conductors supplying two equal L-N loads, that share a common conductor back to the source (that happens to be grounded), then there is no current flow on that conductor. That is a neutral. You can disconnect the neutral and the voltage the two loads see remains the same.

In that same system, if you pull a 12-2 to a lamp or what not, then the white wire in that 12-2 is not a neutral. There's no other phase to offset the returning current. Both conductors in the cable are current carrying conductors.

In a normal 3? 208/120Y system, then not all of the current of the two equal loads is going to return to the source through it's neighboring load and phase conductor - the return conductor (that happens to be grounded) is still used. That's why there's a lengthy formula for determining the neutral load on a 3? 'neutral'.

I'm not quite sure what Tom's getting at.
 

iwire

Moderator
Staff member
"the neutral is always grounded but the grounded is not always a neutral" makes sence to me, but I dont quite understand WHY a grounded is not always a neutral. I have little experience with 3phase, so please excuse my ignorance. Why would you want to ground a phase?

~Matt

Matt, a corner grounded delta system has a grounded conductor that is never 'neutral'.
 

Luketrician

Senior Member
In a residential 1? 120/240 system, if you have two ungrounded conductors supplying two equal L-N loads, that share a common conductor back to the source (that happens to be grounded), then there is no current flow on that conductor. That is a neutral. You can disconnect the neutral and the voltage the two loads see remains the same.
Hey George excuse me if I am wrong but wouldn't the voltage be proportional to the resistance of the two loads if you lost or broke the neutral?
 

dnem

Senior Member
In that same system, if you pull a 12-2 to a lamp or what not, then the white wire in that 12-2 is not a neutral. There's no other phase to offset the returning current. Both conductors in the cable are current carrying conductors.
George,

That used to be how we understood it. . Then '08 added a Neutral Conductor definition that states that the conductor connected to the neutral point is the neutral conductor "that is intended to carry current under normal conditions". . So even when it's carrying full current, it's still considered by the NEC to be a neutral. . Also notice that 310.15(B)(4)(a) does not state, A neutral conductor carries only unbalanced current. . It says, "A neutral conductor that carries only unbalanced current ....." which means that other neutral conductors carry more than just unbalanced current.
 

weressl

Esteemed Member
Matt, a corner grounded delta system has a grounded conductor that is never 'neutral'.
Hm....

I thought that the definition of the neutral in electrical terms that it is neutral in relationship to the ground potential, that the ground conenction that makes that conductor THE neutral.

Isn't it?
 

weressl

Esteemed Member
I understand, however it is in contradiction with prior and current definitions of the neutral. Nor is the present FPN in the Code logical.

'IEEE 141-1993 3.2.5.

[FONT=Times-Roman+2]
b)​
[/FONT][FONT=Times-Italic+2]Three-Phase Systems

[/FONT][FONT=Times-Roman+2]
240/120 Indicates a three-phase, four-wire system supplied from a delta connected transformer. The midtap of one winding is connected to a neutral. The three-phase conductors provide a nominal 240 V three-phase system, and the neutral and the two adjacent phase conductors provide a nominal 120/240 V single-phase system.'

The neutral does not become neutral until it is connected to ground. Until then it is just another 'rouge' phase conductor.

I am just searching for a logical and reasoned defense of the NEC.​
[/FONT]
 

iwire

Moderator
Staff member
5-36 Log #1554 NEC-P05 Final Action: Accept in Principle
(100.Neutral Conductor and Neutral Point)
_____________________________________________________________
TCC Action:
The Technical Correlating Committee directs that the action
on this proposal be sent to the Technical Correlating Committee Task
Group on the definition of ?Neutral Conductor? for review and comment.
Submitter: Technical Correlating Committee on National Electrical Code?,


Recommendation: Add the following definitions to Article 100:

Neutral conductor. A circuit conductor connected to the neutral point of a
system.

Neutral point. The common point of a wye-connection in a polyphase system
or midpoint of a single-phase, 3-wire system or midpoint of a single-phase
portion of a 3-phase delta system or midpoint of a 3-wire, direct-current
system.

Substantiation: This proposal was developed by the TCC Task Group on the
definition of ?Neutral Conductor.? Task Group members were: Jeffrey Boksiner
(Chair) (CMP 5, TCC ), Paul Dobrowsky (CMP 5), Walter Skuggevig (CMP 5),
Doug White (CMP 5), Michael Toman (CMP 2, TCC), Bob Wilkinson (CMP
2), Jim Daly (CMP 6, CMP 7, TCC), Bill Laidler (CMP 6), and Oran Post
(CMP 6).

The definition of ``neutral conductor?? and the associated definition for
?neutral point? is needed in the NEC so that the appropriate conductor can be
identified whenever this term is used in a requirement such as in 250.26 and
250.36. The proposed definition is derived from the IEC definition of ?neutral
conductor? and IEEE Std C57.12.80-2002 definition of ?neutral point.? The
proposed definition was adapted into the NEC language and was expanded to
cover the various cases relevant to the NEC.
The attached figures illustrate the meaning of the proposed definition. Note
that according to the proposed definition ?neutral conductor? exists even where
it does not function as a neutral conductor (that is, where the conductor is not
shared by two or more circuits in the system) as long as it is connected to the
neutral point of the system.
Additional information is available in the Task Group report.

Note: Supporting material is available for review at NFPA Headquarters.

Panel Meeting Action: Accept in Principle
Add the following (two) definitions to Article 100 as follows:

Neutral Conductor. The conductor connected to the neutral point of a system
that is intended to carry current under normal conditions.

Neutral point. The common point on a wye-connection in a polyphase system
or midpoint on a single-phase, 3-wire system, or midpoint of a single-phase
portion of a 3-phase delta system, or a midpoint of a 3-wire, direct current
system.

FPN: At the neutral point of the system, the vectorial sum of the nominal
voltages from all other phases within the system that utilize the neutral, with
respect to the neutral point, is zero potential.
Panel Statement: The revised wording removes the term ?circuit? as was
pointed out in the TCC ballot, there is no definition for a ?circuit conductor?
and the ?neutral conductor? could be in a branch circuit, feeder or otherwise.
The revised text also establishes a differentiation between the ?neutral
conductor? and the ?equipment grounding conductor? which are in fact both
ultimately connected to the neutral point of a system. The differentiation is that
under some normal conditions, the ?neutral conductor? is expected to be
current carrying while under normal conditions the equipment-grounding
conductor is never a current carrying conductor.

Number Eligible to Vote: 15
Ballot Results: Affirmative: 15
_______________________________________________________

.............................
 

jim dungar

Moderator
Staff member
[FONT=Times-Roman+2]The neutral does not become neutral until it is connected to ground. Until then it is just another 'rouge' phase conductor.[/FONT]

[FONT=Times-Roman+2]I am just searching for a logical and reasoned defense of the NEC.[/FONT]


The definition of a neutral has only to due with its relationship to the phase conductors. Its relationship to ground means nothing. In the 240/120 3PH 4W system you cited, the conductor is a neutral to single phase circuit consisting of both phase conductors A & C, in regards to any one phase conductor, including B, it is simply a grounded conductor.

 

weressl

Esteemed Member
.............................
Bob, this is what C57.80 says:

3.272 neutral point:
(A) The common point of a wye-connection in a polyphase system. (B) the point of a symmetrical system that is normally at zero voltage.

My question is 'at zero voltage' in relationship to what? Between what other point and this point does this 'zero voltage' exist? My understanding is and was for the past umpteenth years was the the Earth represent an infinitely large common potential and when one connects to it, it forces that object connected to it to this common potential, that we arbitrarily call "zero". (I say arbitrarily, since I am certain that there is a potential difference exist between the Moon and Earth.):smile:


 
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