Neutral function in 120 or 240

mivey

Senior Member
How do you properly label each wire in this wiring then?
All of the reads and blacks are labeled "conductor". The blude is labeled "grounded conductor".

if voltage is derived from a non CT transformer, does the grounded end get called "grounded side" as opposed to "neutral" ?
correct

Reds are center taps and they're 120,120 and 208 above ground, however are these "neutral" ?
Only for a three-wire system consisting of conductors from each end of a single winding along with a conductor from the center tap of the same winding.
 

mivey

Senior Member
A conductor that is labeled "neutral" but floating more than a negligible amount off ground can lead to shocks.
True. One needs to recognize the difference between a neutral and a grounded conductor.

Kind of like recognizing the difference between a grounded conductor and a grounding conductor. They may sound kind of alike but are really two different things.
 

mivey

Senior Member
There is no common neutral in that drawing. Each red could possibly be called neutral for its associated winding.
To add: That is similar to the high-leg delta. We often call the center-tap the neutral but it is really only the neutral for the 120/240 volt system. For the rest of the system, it is just a grounded conductor.
 

kwired

Electron manager
Location
NE Nebraska
To add: That is similar to the high-leg delta. We often call the center-tap the neutral but it is really only the neutral for the 120/240 volt system. For the rest of the system, it is just a grounded conductor.
I have always considered that one to just be a "grounded conductor" and not a "neutral" but now the NEC defines that particular one as a "neutral". Which it is neutral for the 120/240 single phase portion of the system, but it is not neutral to the entire system.
 

Electric-Light

Senior Member
I have always considered that one to just be a "grounded conductor" and not a "neutral" but now the NEC defines that particular one as a "neutral". Which it is neutral for the 120/240 single phase portion of the system, but it is not neutral to the entire system.
So the middle red would be a neutral that's floating 208v above ground :sick:
 

kwired

Electron manager
Location
NE Nebraska
So the middle red would be a neutral that's floating 208v above ground :sick:
If it came across that way that is not what I meant to say.

In a high leg delta system the neutral is a true "neutral" to the 120/240 single phase portion of the system.

It is not a true neutral to the entire three phase system. To the high leg it is just a point on the system that is 208 volts and happens to be grounded.
 

Electric-Light

Senior Member
If it came across that way that is not what I meant to say.

In a high leg delta system the neutral is a true "neutral" to the 120/240 single phase portion of the system.

It is not a true neutral to the entire three phase system. To the high leg it is just a point on the system that is 208 volts and happens to be grounded.

In this drawing for the system around the middle red wire:
I meant that L1-L2 = 240v, L1-N & L2-N = 120v. So, while it is neutral for that system, it' a neutral with a 208v potential from ground.
 

Smart $

Esteemed Member
Location
Ohio

In this drawing for the system around the middle red wire:
I meant that L1-L2 = 240v, L1-N & L2-N = 120v. So, while it is neutral for that system, it' a neutral with a 208v potential from ground.
Yes, 208V to ground...

...but that is not a typical system. A typical system would not have the upper two red wire connections. Also, the lower red wire connection would be required to be grounded (and not the corner).
 

BPoindexter

Inactive, Email Never Verified
Location
MT Vernon, WA
And remember that the High Leg (B Phase) is required by the NEC to be Orange in color to identify it as such. It would be 208V to ground and it is not allowed to supply a 208V single phase circuit with it. The drawing shown is a cornered grounded system as pointed out by Smart$. I don't know that I have ever seen a schematic like that?
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
And remember that the High Leg (B Phase) is required by the NEC to be Orange in color to identify it as such. It would be 208V to ground and it is not allowed to supply a 208V single phase circuit with it. The drawing shown is a cornered grounded system as pointed out by Smart$. I don't know that I have ever seen a schematic like that?
Where does it say that in the code?
 

eag

Member
Location
Huntsville, AL
The "neutral" conductor carries the imbalance between 2 or 3 different phases sharing that "neutral", i.e. in a 240V single-phase panel, say a load on A draws 5A while a load on B draws 15A and they share a neutral - the current on the neutral is 10A. In a 120V circuit, the white wire you would normally refer to as neutral is actually the "grounded conductor", because there is no imbalance in current to return on this wire.
 

kwired

Electron manager
Location
NE Nebraska
I can't say as I have ever seen it done but what would make it impractical?
First thing is finding a single pole 208 or 240 volt rated circuit breaker, without getting into the 277/480 volt series panels and breakers. It is bad enough just finding a stocking supplier for a straight 240 volt rated breaker if you want to use a double pole for a load connected from high leg to one of the other legs.
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
First thing is finding a single pole 208 or 240 volt rated circuit breaker, without getting into the 277/480 volt series panels and breakers. It is bad enough just finding a stocking supplier for a straight 240 volt rated breaker if you want to use a double pole for a load connected from high leg to one of the other legs.
I would agree. I've often wondered why it is not spelled out in the code that the high leg can't supply line to neutral load, just to make things clear and simple. That would also cover supplying 120/240 ( where only one ungrounded conductor is used for 120 load) rated loads using the high leg, line and neutral should be spelled out as not allowed. These are both age old debates and it seems so easily corrected.
 

kwired

Electron manager
Location
NE Nebraska
I would agree. I've often wondered why it is not spelled out in the code that the high leg can't supply line to neutral load, just to make things clear and simple. That would also cover supplying 120/240 ( where only one ungrounded conductor is used for 120 load) rated loads using the high leg, line and neutral should be spelled out as not allowed. These are both age old debates and it seems so easily corrected.
I don't see that they need to say it is not allowed. If you can find a code compliant way of doing it, what is the problem with it? Say you want to connect a 208 volt heater to circuit composed of high leg to grounded conductor, outside of having difficulty finding a single pole breaker rated to do this with, what is the problem with it? It could be done using fused switch instead of circuit breaker and be code compliant, or only using one pole of a two or three pole breaker with a straight 240 volt rating.
 

Electric-Light

Senior Member
The "neutral" conductor carries the imbalance between 2 or 3 different phases sharing that "neutral", i.e. in a 240V single-phase panel, say a load on A draws 5A while a load on B draws 15A and they share a neutral - the current on the neutral is 10A. In a 120V circuit, the white wire you would normally refer to as neutral is actually the "grounded conductor", because there is no imbalance in current to return on this wire.
Only in split phase. Say a portable classroom fed from 208/120 from A,B and N

If A-N and B-N are both 15A, neutral carries 15A as well. It is a "single phase" service still.
 

gar

Senior Member
121117-2044 EST

Electric-Light:

In your example the neutral has a current of 7.5 A if both loads are resistive. It can be zero by changing the nature of one or both of the loads. If you add an equal 15 A resistive load to the third phase then the neutral current drops to 0. All of these conditions are the same whether the neutral is grounded or not.

I believe a lot of common usage of the word neutral refers to a grounded current carrying conductor.

To get real hung up on the definition of a neutral wire you have to be much more specific in the definition of what a neutral wire is.

.
 

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
Electric-Light:

In your example the neutral has a current of 7.5 A if both loads are resistive.
This is not correct. 15A would be correct, in this example.

It can be zero by changing the nature of one or both of the loads. If you add an equal 15 A resistive load to the third phase then the neutral current drops to 0. All of these conditions are the same whether the neutral is grounded or not.
This is correct. Neutral doesn't mean grounded conductor (although neutrals can be grounded) it means the common point on a wye, or the midpoint on a single phase 3 wire system, or the midpoint of the single phase portion of a 4 wire delta system.
 
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