Neutral Conductor and Grounded Conductor

[mikoal]

So I was reading my code book the other day and found out that a neutral is always considered a grounded conductor assuming it follows the code. However a grounded conductor isnt always a neutral

IE:

http://forums.mikeholt.com/showthre...unded-conductor-pertaining-to-the-same-thing?

and

"IEEE dictionary defines the neutral as the conductor with an equal potential difference between it and the other output conductors of a 3-wire or 4-wire system. (so on a wild leg 120/240V system, for instance, there is a grounded conductor but not a neutral)"

however what i dont get is in a house system its a single phase 120/240 center tapped to get the 120V. why is this not a neutral?
it is a return path for curent, and is equal potential to the other outputs (120 each) but its single phase.

 

[roger]

however what i dont get is in a house system its a single phase 120/240 center tapped to get the 120V. why is this not a neutral?
it is a return path for curent, and is equal potential to the other outputs (120 each) but its single phase.

It is a neutral, why do you think it is not?

Roger

 

[mikoal]

It is a neutral, why do you think it is not?

Roger

IEEE and the CEC says it is not considered a neutral. For a neutral is defined as "The conductor (when one exists) of a polyphase circuit or single phase, 3 wire circuit that is intended to have a voltage such that the voltage differences between it and each of the other conductors are approximately equal in magnitude and are equally spaced in phase."

 

[raider1]

It would be a neutral conductor.

Check out the definition of neutral point that was added to Article 100 in the 2008 NEC.

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

Chris

 

[david luchini]

IEEE and the CEC says it is not considered a neutral. For a neutral is defined as "The conductor (when one exists) of a polyphase circuit or single phase, 3 wire circuit that is intended to have a voltage such that the voltage differences between it and each of the other conductors are approximately equal in magnitude and are equally spaced in phase."

Isn't this exactly what you have described? The definition you give says it is a neutral.

 

[mikoal]

It would be a neutral conductor.

Check out the definition of neutral point that was added to Article 100 in the 2008 NEC.

Chris

What about in a 2 wire single phase system with one of the wires being grounded and is the return conductor?

 

[raider1]

What about in a 2 wire single phase system with one of the wires being grounded and is the return conductor?

Then there would be no neutral just a grounded conductor.

Chris

 

[mikoal]

Then there would be no neutral just a grounded conductor.

Chris

ahhh ok there was my confusion. Sorry everyone!

So now why isn't this considered as a neutral, it seems to serve the same function as a neutral.

Also this single phase 2 wire circuit with one of the conductors grounded.......what is an example of this?
I was thinking of a regular single phase 240V, but i dont know if one of the legs were grounded......




I've read on the IMSA Journal Feature Article Jan/Feb 2003. Not sure how accurate this is.

"A grounded conductor is not always a neutral, for example in a 120/240V 3 phase high leg delta, the grounded conductor is not a neutral because it is not a solidly grounded system"

however in your quote.

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

Are these contradicting each other?

Edit: Added more info

 

[roger]

ahhh ok there was my confusion. Sorry everyone!

So now why isn't this considered as a neutral, it seems to serve the same function as a neutral.

Because it carries the same current as the ungrounded conductor

Also this single phase 2 wire circuit with one of the conductors grounded.......what is an example of this?

Any standard 120 v two wire circuit.

I was thinking of a regular single phase 240V, but i dont know if one of the legs were grounded......

In general as far as US electrical distribution is concerned, 240 v circuits will consist of two ungrounded conductors


Here are a couple of simple illustrations

A two wire circuit

A true neutral

Roger

 

[david luchini]

So now why isn't this considered as a neutral, it seems to serve the same function as a neutral.

How would this be serving the same function as a neutral? You will not have "voltage such that the voltage differences between it and each of the other conductors are approximately equal in magnitude and are equally spaced in phase."

Also this single phase 2 wire circuit with one of the conductors grounded.......what is an example of this?
I was thinking of a regular single phase 240V, but i dont know if one of the legs were grounded......

If you had a situation where you had a single phase 480-120V transformer to supply a specific load. 250.20(B) would require the 120V system to be grounded.

 

[mikoal]

Because it carries the same current as the ungrounded conductor

Any standard 120 v two wire circuit.

In general as far as US electrical distribution is concerned, 240 v circuits will consist of two ungrounded conductors


Here are a couple of simple illustrations

A two wire circuit

A true neutral

Roger

Wow thanks for the illustration!
I guess why I was confused was because it looks identical to a regular center tap, but just that the other leg isn't used or connected.

So if we have your center tapped scenario, where the grounded conductor is a true neutral, and one of the legs are never connected to a load, then wouldnt it look the same as the first diagram, where current only flows in that one hot side?

How would this be serving the same function as a neutral? You will not have "voltage such that the voltage differences between it and each of the other conductors are approximately equal in magnitude and are equally spaced in phase."
If you had a situation where you had a single phase 480-120V transformer to supply a specific load. 250.20(B) would require the 120V system to be grounded.

Can you say that since there is only 1 other conductor that it is the same in mag and phase?

 

[roger]

Wow thanks for the illustration!
I guess why I was confused was because it looks identical to a regular center tap, but just that the other leg isn't used or connected.

You're welcome

So if we have your center tapped scenario, where the grounded conductor is a true neutral, and one of the legs are never connected to a load, then wouldnt it look the same as the first diagram, where current only flows in that one hot side?

Yes it would, see the illustration below for an unballanced scenario

Roger

 

[mikoal]

You're welcome

Yes it would, see the illustration below for an unballanced scenario

Roger

You mentioned that any regular 120V 2 wire circuit would be using a grounded conductor instead of neutral.......

Would a receptacle be considered a 2 wire circuit? It seems to me its a 3 wire system but only 2 of the 3 is used for that 1 receptacle. But still a 3 wire system

So if receptacle is using a 3W system, why/when would anyone use the 2 wire System?

Also why wouldnt a 120V 2 wire circuit act like a 240 2 wire? both ungrounded?.......oh wait i recall reading something long the lines of <150V ac systems must be grounded.....