# Neutral function in 120 or 240

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• 10-28-12, 11:10 PM
jynx1
Neutral function in 120 or 240
I'm confused on neutral completing a 120 or 240 volt circuit relative to the hot(s) and then having 0 voltage when relative to ground... How can it circumstantially have two different voltages?

Also, if we're dealing with 120 volt AC outlet 60hz single phase circuit, is the neutral still an alternating current conductor? Again and again I've read that the neutral in 120 solely carries the current to ground... that sounds like the characteristics of a dc circuit... so, if no voltage is applied to (maybe because it's a single phase circuit therefore poles donnot reverse) the neutral, the current takes the lease resistive path to ground, which in essence completes the 120 v circuit.

Is this correct? I'd like to know so I can discuss some other electrical ideas.

Thanks for any help!
• 10-28-12, 11:36 PM
Smart \$
Quote:

Originally Posted by jynx1
I'm confused on neutral completing a 120 or 240 volt circuit relative to the hot(s) and then having 0 voltage when relative to ground... How can it circumstantially have two different voltages?

The 120V measurements are referenced to the grounded neutral (steady-state 0 volts measured ground to neutral). Each "hot" to ground voltage is an AC voltage, but using either as the reference, the other's cycle is 180° out of phase. Measuring across the two "hots" gives you 240V.
• 10-28-12, 11:45 PM
Smart \$
Quote:

Originally Posted by jynx1
...

Also, if we're dealing with 120 volt AC outlet 60hz single phase circuit, is the neutral still an alternating current conductor? Again and again I've read that the neutral in 120 solely carries the current to ground... that sounds like the characteristics of a dc circuit... so, if no voltage is applied to (maybe because it's a single phase circuit therefore poles donnot reverse) the neutral, the current takes the lease resistive path to ground, which in essence completes the 120 v circuit.

Is this correct? I'd like to know so I can discuss some other electrical ideas.

Thanks for any help!

Current always returns to its source. With utility power, this is typically the service transformer. While the ground (earth) may carry a little of the current, typical premises wiring is designed to minimize such current.

Neutral conductors in two-wire circuits carry just as much current as the circuit hot. Neutral conductors in three-wire 120/240 circuits carry the unbalanced current of the two half circuits. With two identical loads connected L1-N and L2-N, there will be no current through the neutral conductor because the current through one half of the circuit is the very same current through the other half.
• 10-28-12, 11:53 PM
jynx1

So even though the current is alternating, it still in essence is a direct path back to the transformer because it is grounded to the center tap transformer? It can 'feed' the circuit the same as the hot, though?
• 10-29-12, 12:10 AM
ActionDave
Quote:

Originally Posted by jynx1
I'm confused on neutral completing a 120 or 240 volt circuit relative to the hot(s) and then having 0 voltage when relative to ground... How can it circumstantially have two different voltages?

Also, if we're dealing with 120 volt AC outlet 60hz single phase circuit, is the neutral still an alternating current conductor? Again and again I've read that the neutral in 120 solely carries the current to ground... that sounds like the characteristics of a dc circuit... so, if no voltage is applied to (maybe because it's a single phase circuit therefore poles donnot reverse) the neutral, the current takes the lease resistive path to ground, which in essence completes the 120 v circuit.

Is this correct? I'd like to know so I can discuss some other electrical ideas.

Thanks for any help!

Read this http://forums.mikeholt.com/showthrea...650#post708650 and see if it helps. I think it will and explains things better than I can.
• 10-29-12, 02:18 AM
Smart \$
Quote:

Originally Posted by jynx1

So even though the current is alternating, it still in essence is a direct path back to the transformer because it is grounded to the center tap transformer? It can 'feed' the circuit the same as the hot, though?

The more appropriate term is connected. The current will be the same if the neutral connection were not grounded.

A comparative analogy would be a two series-connected batteries, where each half of the transformer winding is represented by one battery, and the center tap connection is the junction point of the two batteries. How much and where the current flows is determined by the connected load.
• 10-29-12, 09:24 AM
infinity
I agree with Smart that the two battery analogy is a good way to understand how the 120/240 volt system is connected. When I occasionally use it to explain how it works you simply stress that you need to disregard the battery polarity.
• 10-29-12, 10:35 AM
Electric-Light
The "center tap" doesn't even have to be ground. You can have one end grounded and still have 0-120-240 rather than 120-0-120.

It's neutral only because its referenced to ground.
• 10-30-12, 12:41 PM
david luchini
Quote:

Originally Posted by Electric-Light
The "center tap" doesn't even have to be ground. You can have one end grounded and still have 0-120-240 rather than 120-0-120.

It's neutral only because its referenced to ground.

I don't believe this is correct. The neutral point is the midpoint on a single-phase, three wire system. In your listed references, the neutral in the first is at "120" and the in the second is at "0." (0-120-240 and 120-0-120)
• 10-30-12, 12:55 PM
Speedskater
While it's technically correct, it's not applicable to typical NEC single phase wiring systems.
• 10-30-12, 01:01 PM
kwired
Quote:

Originally Posted by Electric-Light
The "center tap" doesn't even have to be ground. You can have one end grounded and still have 0-120-240 rather than 120-0-120.

It's neutral only because its referenced to ground.

I agree with David.

We call the center tap neutral, mostly because it is equal to all the other points on the system.

You could have a single winding with 100 taps somewhere mid winding. You can only ground one point, whether it be one end of the winding or one of the taps. If you ground more than one point you have a short circuit between those two points.

We ground conductors that are not a "neutral" in simple two wire supplies, or in three phase three wire corner ground systems. Even in DC circuits often the negative is referred to as 'ground' but this is true only because the negative conductor of the source is actually grounded someplace. You can ground the positive terminal and things will work just fine, some electronics devices will not work, but is by design more so than the fact that it can't work. Some old automobiles or other machinery they did ground the positive instead of the negative. That just means the frame of the machine is at same potential as the positive instead of the negative, current still flows the same paths and direction (with DC).

General rules in NEC usually require the "Neutral" to be the conductor that gets grounded, but if there is no "neutral" then pretty much any point in the system can be grounded.

We ground systems to make a reference to earth, and we extend this grounded conductor to all non current carrying metallic components of our system and call it the equipment grounding conductor. The purpose of the equipment grounding conductor is to create a low resistance path so if an ungrounded conductor comes into contact with one of the grounded components there will easily be a high level of current that flows which will in turn cause overcurrent protection devices to open the circuit preventing further damages or injuries to people.
• 10-30-12, 01:05 PM
jim dungar
Quote:

Originally Posted by Electric-Light
The "center tap" doesn't even have to be ground. You can have one end grounded and still have 0-120-240 rather than 120-0-120.

Correct.

Quote:

Originally Posted by Electric-Light
It's neutral only because its referenced to ground.

Incorrect.
The connection to ground is immaterial.
It is the neutral because it is 'half way' between the the other conductors.
• 10-31-12, 08:35 AM
Electric-Light
Quote:

Originally Posted by jim dungar
Correct.

Incorrect.
The connection to ground is immaterial.
It is the neutral because it is 'half way' between the the other conductors.

Are you sure about that? Center tap is not required for neutral.

In Norway, there is 230v delta, ungrounded. All the power at receptacles come from any two of three.

In some places, they use corner grounded delta, let's say u.
u=N/L1, v=l2,w=l3. so, its still 230v in whatever way but uv and uw yields L-N, vw yields L-L.
it is neutral as far as wiring is concerned, because it is bonded to ground, so that wire has no voltage with respect to ground.

If for some reason you choose to bond one of the branch on a 208Y/120 setup, and leave the not floating you'll have....
with respect to ground... 0, 208, 208, 120v(the knot). Even though the knot is in between all the wires, it would be improper to call the knot "neutral" because, it will be 120v above ground.
• 10-31-12, 08:50 AM
mivey
Quote:

Originally Posted by Electric-Light
Are you sure about that? Center tap is not required for neutral.

If it were not the center-tap, it would not be the neutral but just the grounded conductor. It is a loose terminology issue because some people loosely call the grounded conductor a "neutral" when it is not.

Quote:

Originally Posted by Electric-Light
...In some places, they use corner grounded delta, let's say u...it is neutral as far as wiring is concerned

It is the grounded conductor, not a neutral.

Quote:

Originally Posted by Electric-Light
...with respect to ground... 0, 208, 208, 120v(the knot). Even though the knot is in between all the wires, it would be improper to call the knot "neutral" because, it will be 120v above ground.

That is because of loose terminology again. The "knot" is the neutral point of the phase conductors, even if we ground one of the phase conductors. If you want to be correct, you should distinguish between a grounded conductor and a neutral conductor. If you are just talking to someone using loose terminology and everyone knows what you meant, then it is not such a big deal.
• 10-31-12, 09:54 AM
petersonra
It is not unusual for people to refer to the grounded conductor as "neutral", even when it really is not the circuit neutral.
• 10-31-12, 10:06 AM
kwired
Quote:

Originally Posted by petersonra
It is not unusual for people to refer to the grounded conductor as "neutral", even when it really is not the circuit neutral.

True, but they are setting themselves up for misunderstandings when they run into a grounded conductor that is not a neutral.
• 10-31-12, 11:05 AM
petersonra
Quote:

Originally Posted by kwired
True, but they are setting themselves up for misunderstandings when they run into a grounded conductor that is not a neutral.

not unlike when they call both the EGC and the GEC "the ground".
• 11-01-12, 03:25 PM
Electric-Light
How do you properly label each wire in this wiring then?

http://i.imgur.com/ARMW9.png

The blue is not a center tap, yet its grounded. if voltage is derived from a non CT transformer, does the grounded end get called "grounded side" as opposed to "neutral" ?

Reds are center taps and they're 120,120 and 208 above ground, however are these "neutral" ?
• 11-01-12, 03:30 PM
Electric-Light
I suppose this is one of those semantics thing like inflammable, which means that it *is* flammable, however non-flammable and flammable are preferred, because inflammable can be misinterpreted as "it does not burn" and here technical/grammatical accuracy is of lesser importance than consequences of misunderstanding.

A conductor that is labeled "neutral" but floating more than a negligible amount off ground can lead to shocks.
• 11-01-12, 07:07 PM
kwired
Quote:

Originally Posted by Electric-Light
How do you properly label each wire in this wiring then?

http://i.imgur.com/ARMW9.png

The blue is not a center tap, yet its grounded. if voltage is derived from a non CT transformer, does the grounded end get called "grounded side" as opposed to "neutral" ?

Reds are center taps and they're 120,120 and 208 above ground, however are these "neutral" ?

There is no common neutral in that drawing. Each red could possibly be called neutral for its associated winding, but they are not grounded conductors, and if you were to connect this to some panelboard for power and lighting, you would need overcurrent devices on each of the red conductors also, so the panel would have five ungrounded buses.

The blue conductor that is grounded is exactly that - the "grounded conductor". It would need to be grounded either at the source or at the first disconnect, and then all equipment grounding conductors separated from current carrying "grounded" conductors just like any other system with a grounded conductor.

Kind of a clever way to get 120 volts from all three phases of a delta system, but finding a panelboard that would work with it would likely cost more than just using a wye transformer.
• 11-01-12, 07:12 PM
mivey
Quote:

Originally Posted by Electric-Light
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".

Quote:

Originally Posted by Electric-Light
if voltage is derived from a non CT transformer, does the grounded end get called "grounded side" as opposed to "neutral" ?

correct

Quote:

Originally Posted by Electric-Light
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.
• 11-01-12, 07:15 PM
mivey
Quote:

Originally Posted by Electric-Light
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.
• 11-01-12, 07:20 PM
mivey
Quote:

Originally Posted by kwired
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.
• 11-02-12, 07:44 AM
kwired
Quote:

Originally Posted by mivey
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.
• 11-02-12, 03:03 PM
Electric-Light
Quote:

Originally Posted by kwired
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:
• 11-03-12, 09:04 AM
kwired
Quote:

Originally Posted by Electric-Light
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.
• 11-03-12, 07:51 PM
Electric-Light
Quote:

Originally Posted by kwired
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.

http://i.imgur.com/ARMW9.png
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.
• 11-03-12, 09:33 PM
Smart \$
Quote:

Originally Posted by Electric-Light
http://i.imgur.com/ARMW9.png
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).
• 11-13-12, 03:06 PM
BPoindexter
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?
• 11-13-12, 03:20 PM
petersonra
Quote:

Originally Posted by BPoindexter
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?
• 11-13-12, 04:10 PM
eag
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.
• 11-13-12, 05:41 PM
jaggedben
The grounded DC conductor on a solar system is another example of a grounded conductor that is not a neutral.
• 11-14-12, 08:45 AM
kwired
Quote:

Originally Posted by petersonra
Where does it say that in the code?

I have same question. Other code sections make it pretty much impractical to use it that way, but I find nothing that straight up prohibits doing so either.
• 11-14-12, 10:56 AM
petersonra
Quote:

Originally Posted by kwired
I have same question. Other code sections make it pretty much impractical to use it that way, but I find nothing that straight up prohibits doing so either.

I can't say as I have ever seen it done but what would make it impractical?
• 11-14-12, 11:37 AM
kwired
Quote:

Originally Posted by petersonra
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.
• 11-14-12, 11:57 AM
texie
Quote:

Originally Posted by kwired
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.
• 11-14-12, 12:04 PM
kwired
Quote:

Originally Posted by texie
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.
• 11-17-12, 06:02 PM
Electric-Light
Quote:

Originally Posted by eag
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.
• 11-17-12, 08:55 PM
gar
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.

.
• 11-17-12, 09:53 PM
david luchini
Quote:

Originally Posted by gar
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.

Quote:

Originally Posted by gar
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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