K8MHZ
Senior Member
- Occupation
- Electrician
That's the case with most portable AC generators. Sure there's a ground lug on the frame, but how often is it used and is the neutral bonded to the frame? They come both ways.
? Neutral ? Why do they call it that?
- Thread starter Russell Ensslin
- Start date
- Status
That's the case with most portable AC generators. Sure there's a ground lug on the frame, but how often is it used and is the neutral bonded to the frame? They come both ways.
K8MHZ
Senior Member
- Occupation
- Electrician
Still the same principal. In the DC system, the neutral point is midway between the + and - DC source poles. I think the key is the word 'midway'. All the neutrals I have seen have been midway between something.
What if there is no midway point? Like the output of a rectifier for example?
K8MHZ
Senior Member
- Occupation
- Electrician
I guess I don't see how the output of a single rectifier could have a neutral.
You do bring up a good point. What about a 120 volt only single phase generator with no neutral to anything bond? They still have a neutral, as in hot and neutral conductors. How do 'they' decide which leg of a 120 volt, single voltage, floating neutral supply is actually the neutral, and, is it really a neutral????
Good and thoughtful post. Thank you.
A couple of points if I may.
I've done the power circuit design for a good many high current (40kA is not unusual) controlled rectifiers in the field of anodising and other LV applications. SCRs.
The usual arrangement is hexaphase - a balance between rectifier losses and transformer losses but that's for another time and place. It's like the six spokes of a wheel with the negative being the star point or hub if you like. Would you/should you call that star point a neutral? I wouldn't and didn't.
The second point on the single phase 120V system you mentioned. I don't think you can call either leg neutral.
Carultch
Senior Member
- Location
- Massachusetts
This is an instance where there is a groundED conductor, without there being a neutral. That is to say, there is no current-carrying conductor with a voltage that is "equidistant" from the voltages of all other ungrounded current-carrying conductors.
Gary Glaenzer
Member
Neutral ? Why do they call it that?
Neutral ? Why do they call it that?
Is that why they call they call the grounded conductor the neutral?
Please break down responses as though you were addressing a novice as I need that.[/QUOTE]
Simplest explanation I can come up with:
Consider the typical single-phase 120-0-120 service
At any given time, the two 'line' ( the 120's in 120-0-120) voltages will be of equal voltages but opposite polarities.
So the center ( '0' ) point ( 'neutral') will be at the mid-point of the voltages, which, being equal but opposite, will be 0 volts.
Analogy: Think of a vehicle's gear shift.....Reverse-Neutral-Foward ('Drive') equal but opposite with Neutral at the '0' point.
Hope this helps
Neutral ? Why do they call it that?
Is that why they call they call the grounded conductor the neutral?
Please break down responses as though you were addressing a novice as I need that.[/QUOTE]
Simplest explanation I can come up with:
Consider the typical single-phase 120-0-120 service
At any given time, the two 'line' ( the 120's in 120-0-120) voltages will be of equal voltages but opposite polarities.
So the center ( '0' ) point ( 'neutral') will be at the mid-point of the voltages, which, being equal but opposite, will be 0 volts.
Analogy: Think of a vehicle's gear shift.....Reverse-Neutral-Foward ('Drive') equal but opposite with Neutral at the '0' point.
Hope this helps
Carultch
Senior Member
- Location
- Massachusetts
I guess you could make the gear shift analogy, but remember that neutral is still part of the power transmission for electricity. The neutral gear setting in a vehicle means that you've disconnected the engine from the wheels, so that the two shafts spin independently, and therefore cannot transmit power.
An analogy I would use, is to think of sea level as the grounded conductor/neutral. And think of a pump that raises water to a reservoir above sea level, and another pump that raises water from a reservoir below sea level back to the sea. The two reservoirs are your ungrounded sources/sinks of water. The neutral sea level is your grounded soruce/sink of water. Pumps bring water up, water passes through a turbine load on its way down, and back to the lower sea or reservoir. You can either connect a turbine load between the upper reservoir and the sea (analogous to a single phase 120V load on Line 1), between the sea and the lower reservoir (analogous to a single phase load on Line 2), or between the upper and lower reservoir (analogous to a 240V load across the two lines).
In this analogy, the neutral grounded conductor would be a pipe at sea level. It still carries the water from/to the load, but there is no elevation of it above sea level, and negligible pressure difference across its length. The pipes either above or below sea level are your ungrounded conductors, and the reservoirs/pumps are your source.
Voltage would be analogous to elevation. Current would be analogous to the flow rate of water. The combination of the two, form the power transmitted from pump source to turbine load.
Last edited:
K8MHZ
Senior Member
- Occupation
- Electrician
How is there a grounded conductor on a 120 volt generator with a floating neutral?
Carultch
Senior Member
- Location
- Massachusetts
There really isn't. In the case of a floating generator, which has neither polarity connected to ground or even to the chassis, there is no grounded conductor. I'm anticipating that the generator would eventually connect to a place where this is bonded, if it is used as a backup grid-replacement generator.
In the case of a floating generator output, both current-carrying conductors are ungrounded, and neither is neutral. Although one of them can still carry the current that a neutral ordinarily carries, when serving most loads that would otherwise be supplied from a single line and neutral of the 3-wire Edison system.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
That IMO is the basic concept of defining "neutral" is a point that is midway. This is obvious with single phase with a midpoint or the common point of a wye system.
Two wire systems - not possible to have a "neutral", you can ground either side though. Two wire DC - you can ground either side but does effect polarity in relation to ground, three wire DC with center grounded will always have one side that is positive in relation to ground and the other side negative, I still think that is close enough to call neutral.
Only fairly recently has NEC recognized the mid point of a delta system with one side grounded at midpoint as a neutral conductor, probably 2005 or later can't remember for certain, before then NEC did not really recognize that grounded conductor of that system as a neutral conductor, and IMO it isn't in relation to the entire system but is neutral to the one side of the delta and does perform same way as a single phase system midpoint if you only consider single phase loads on that side of the delta.
Three wire delta? There is no one conductor that is midway - they are all equal distant to one another potential wise, just like the two conductors of a two wire supply.
In your explanation the "mid point" is the "neutral" we still have to actually "ground" it before it becomes a grounded conductor. Same source could have one of the other two points of the system grounded, but the mid point will still be 120 volts to each end and will not be at ground potential. NEC happens to require in almost all instances that a system that is grounded use the neutral (if there is a neutral) to be the conductor that is grounded.
Last edited:
Russell Ensslin
Member
- Location
- Olivehurst California
- Location
- Massachusetts
What about a ground fault? That would be a Grounded conductor.
Not to the NEC.
To the NEC the grounded conductor is the intentionally grounded conductor not the accidentally faulted conductor.
romex jockey
Senior Member
- Location
- Vermont
- Occupation
- electrician
Noodle.....
Noodle.....
Pop Quiz..!
Find the noodle....
Types of earthing systems
NEC (TN-C-S) >>>
TN-S >>>
TT>>>
~RJ~
Noodle.....
Pop Quiz..!
Find the noodle....
Types of earthing systems
NEC (TN-C-S) >>>
TN-S >>>
TT>>>
~RJ~
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
First two do not have a neutral - they are two wire sources, last one does not show the source - so we really do not know if it is a supplied from a two wire source or just two wires of a multiwire source.
You have to have a multiwire source to have a neutral. All the examples shown do have a grounded conductor though.
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
Yes, the NEC definition explicitly includes the "midpoint of a 3-wire direct current system". And what I said above about measuring voltages holds true as well.
I guess we should clarify: we're talking nominal voltages here. Physics does not dictate the zero.
romex jockey
Senior Member
- Location
- Vermont
- Occupation
- electrician
romex jockey
Senior Member
- Location
- Vermont
- Occupation
- electrician
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
I think the million dollar question is: what is the definition of neutral?
Is it a conductor which is referenced to earth, or one which has a symmetrical phase angle in relative to two or more live conductors?
My question to you: in a 2 phase 3 wire system (see this: http://electrical-engineering-porta...tribution-of-ac-power#two-phase-3-wire-system), is the midpoint conductor a neutral conductor?
- Occupation
- Licensed Electrician
What year was it that the NEC changed the definition of a neutral?
- Status