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3 minutes ago, Marc said:

No.  Neutral is always a grounded conductor.

Why?

And then let me push back a little bit.  From the NEC, the definition of neutral conductor and neutral point are:

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 (fine print note):  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. 

These definitions don't seem to require any type of grounding.  At the neutral point of a standard 120/240 system, where our "neutral" conductor attaches at the transformer, isn't the vectorial sum of the voltages from the other phases equal to zero, regardless of whether or not this conductor is grounded?

 

neutral point.png

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Grounding has nothing to do with the lack of a voltage vector on the neutral of a balanced configuration.  Not all configurations are balanced. A three wire delta configuration with the neutral taken at the center-point of one of the legs (which creates a high leg) is a common example of an unbalanced system.

Neutral grounding requirements are found elsewhere in the NEC.

Edited by Marc

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Vector math becomes very simple when done graphically. Vectors are just magnitude, like any ordinary number, but with a direction.  A car going North at 60 mph is a vector. 60 mph is the magnitude and North is the direction.

https://www.khanacademy.org/math/precalculus/x9e81a4f98389efdf:vectors/x9e81a4f98389efdf:vector-add-sub/v/visually-adding-and-subtracting-vectors

 

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1 hour ago, Marc said:

Grounding has nothing to do with the lack of a voltage vector on the neutral of a balanced configuration. 

Yes, but that's my point.  Or my question.  Or something.  Grounding has nothing to do with whether or not the point X0 in my diagram is the neutral point.  If that's true then the conductor coming from that X0 point is neutral whether or not the system is grounded.  

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8 hours ago, SNations said:

Would what we colloquially call the "neutral conductor" still be neutral if it wasn't grounded?

Steve

Before 2008, the XO point on your drawing would not have been considered a neutral point and the wire connected to it would have been properly called the "grounded conductor." There's nothing particularly "neutral" about that conductor (unless it happens to be part of a multi-wire circuit). However, *everyone* called it the "neutral" so the NEC decided to go with the flow and adopt the name in 2008. 

In a single-phase, 120/240 volt system that conductor must be grounded and it may be called the neutral. Of course, the presence or absence of grounding doesn't change it's "neutralness," which it doesn't really have in the first place. 

A better question might be why the ungrounded conductor is called a neutral when it's not neutral. (And the answer is: because everyone calls it that.) 

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Thanks for the reply.

6 hours ago, Jim Katen said:

Before 2008, the XO point on your drawing would not have been considered a neutral point and the wire connected to it would have been properly called the "grounded conductor." 

I understand that this definition was added in 2008, but nothing physically changed then, right?  So if this was a neutral point in 2008 then it was a neutral point in 2007, wasn't it?  But specifically to the point, doesn't it look like at the neutral point the vectorial sum of the nominal voltages from the two live phases is zero?

6 hours ago, Jim Katen said:

 There's nothing particularly "neutral" about that conductor (unless it happens to be part of a multi-wire circuit).

But isn't that the case?  Isn't the service entrance just a big multi-wire circuit?  That seems to be the crux of the issue.

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Jim, your reply actually helped me quite a bit to understand this better.

But I might not have been clear in my original question, if so I'm sorry about that.  I'm not so much interested in some random "neutral" wire running through your house.  I'm interested in the grounded service entrance conductor running from the transformer in to your service panel.  Would that conductor still be neutral if it wasn't grounded?  

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Sorry, I didn't realize you were asking about the service neutral. 

My opinion: yes. It's a neutral whether it's grounded or not. It carries only the imbalance of the loads on the other two conductors. 

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