Difference between neutral and ground

[sirsajid]

What is the difference between neutral and ground??
one more question what is the practical example of current source

 

[tiny-tim]

welcome to pf!

hi sirsajid! welcome to pf!

What is the difference between neutral and ground??

neutral is part of the circuit … touch it and you die

ground (or earth) is not part of the circuit (unless something goes wrong)

one more question what is the practical example of current source

not sure what you mean by "current source"

 

[cmb]

(Did you bother to do a search for this topic?)

See;

https://www.physicsforums.com/showthread.php?t=539162

&

https://www.physicsforums.com/showthread.php?t=526008

&

https://www.physicsforums.com/showthread.php?t=382007

&c.

 

[gnurf]

what is the practical example of current source

A voltage source in series with a resistor.

 

[sirsajid]

hi sirsajid! welcome to pf!


neutral is part of the circuit … touch it and you die

ground (or earth) is not part of the circuit (unless something goes wrong)


not sure what you mean by "current source"

I mean example of voltage source is battery. Can u give me the example of current source?

 

[DragonPetter]

hi sirsajid! welcome to pf!


neutral is part of the circuit … touch it and you die

Really? I thought neutral is tied to ground at the tansformer output place. Isn't only dangerous to touch if there is a short circuit somewhere so that neutral is no longer at ground potential?

 

[Averagesupernova]

Tiny-tim is certainly not telling the whole story. It is generally not a good idea to touch anything connected with mains electricity until the power is off. However, touching the neutral will not kill you unless there are some wiring problems. It is done all the time.
-
Here is an example of where you can get into trouble with a neutral: Suppose you have a ceiling light you wish to replace and in doing so you don't bother switching the power off since the wall switch is off. Again, not a good idea, but it is done all the time. You assume since the wall switch is off there should be no problems. BUT, power is routed into the ceiling light box and continues farther down the circuit to the next light/outlet. The light itself you are working on does not have power on it since the wall switch is off, but when the neutrals are disconnected in order to replace the light you have interupted the devices down the circuit. Now the neutral coming back will have a voltage on it.

 

[psparky]

A voltage source in series with a resistor.

In other words...there is no such thing as a current source. There are only voltage potentials with potential loads. V=IR. The V and the R determine the current. Current sources are just tools used in school to help you learn.

So you can say that a voltage source in series with a resistor is a current source...but really the Voltage and the load (resistance) are determining the current. Good question though...I remember thinking the same thing in college.

What is difference between nuetral and ground. Another good question. In simplest terms...take your breaker panel at home. Assuming you are USA...the ground and nuetral are actually tied together in the breaker panel! The ground and the nuetral obviously go to the loads...but it's probably the other end you are interested in...well, the ground simply goes to the ground. In other words, it gets buried in the Earth. The non load side of the neutral goes to the center tap of the transformer on the pole...delivering 120 Volts instead of line to line voltage of 240V. If you are holding a 120V hot wire (dry condition...insulated boots...don't ever grab a hot wire, just hypothetically saying)...touching either nuetral or ground will complete the circuit.

On the load side, the grounds are used to keep everything at zero potential...and equally if not more important, the ground is there to trip the breaker in the case that the hot wire comes loose and sits on the washing machine for example. Without the ground the hot wire will make the washing machine "hot". Mom walks up to it touches it and gets electricuted. If the washing machine has a ground...the second the hot wire touches the chasis...it immediately trips the breaker. Mom goes to reset breaker and it doesn't reset. Mom calls repair man...he installs hot wire back in place...resets breaker...all is well...mom is happy.

 

[DragonPetter]

In other words...there is no such thing as a current source.

I would not go this far. When you talk about a source, usually you mean it is supplying something to a load. A voltage source is equally valid as a current source, they are a duality (for example, thevenin and norton equivalence). The difference between the two I think is more of a convention issue, as it is which is being regulated/held constant or which your load is dependent on.

You can design a source that's voltage changes as the external load changes to keep a constant current, and then I'd call it a current source. Ion chambers are also usually considered current sources, since the ion pairs are generated by radiation and source a current.

 

[psparky]

I would not go this far. When you talk about a source, usually you mean it is supplying something to a load. A voltage source is equally valid as a current source, they are a duality (for example, thevenin and norton equivalence). The difference between the two I think is more of a convention issue, as it is which is being regulated/held constant or which your load is dependent on.

You can design a source that's voltage changes as the external load changes to keep a constant current, and then I'd call it a current source. Ion chambers are also usually considered current sources, since the ion pairs are generated by radiation and source a current.

I agree 100%

 

[sirsajid]

I agree 100%

Thanx for giving me good response. I am new to this forum. I never joined any forum before. I ll be a regular user of this forum now onwards.
i have seen on net written van de graaff generator is a current source.

 

[jim hardy]

the bottom end of a lightning bolt would be a good example of a current source.

It's going to develop whatever voltage is necessary to dump its charge into earth.
.....

read those old threads on neutral vs earth. It is a matter of definition and is widely mis-understood.

 

[Rogerio]

...what is the practical example of current source

This is commonly used as a (constant) current source:

 

[Roar]

What is the difference between neutral and ground??
one more question what is the practical example of current source

In American electrical wiring there is a black covered wire that is hot in relationship to the white and green wires. the reason there are two of these is that the white one is to provide the other side of the electrical circuit. current flows back and forth through these two in that it is alternating current so depending what the potential of one of those is determines which way it flows. The green wire is the 'safety ground', it is connected to any exposed metal of anything connected to power to carry any current that is inadvertently on that metal due to what is called a fault caused by defect.
both the white and green wires are connected to a grounding stake at the main disconnect.
Michael
Sr Consultant
EMC

 

[jim hardy]

The white neutral wire is one half of the normal ppower circuit, you could think of the black "hot" as supply line and white "neutral" as return line.

The green "ground" wire does not carry any current unless there is an insulation failure in the appliance. The idea is for 'fault' current (from failed insulation) to return to the supply transformer through the green "ground wire" instead of through your hands, torso, feet, and ground. . If there is any fault current that Green wire should be the path of least resistance, keeping tiny hands safe..

 

[metiman]

As Rogerio showed, a current source is generally the output of a transistor or tube or other nonlinear active circuit element. Batteries and generators are considered voltage sources. It is generally a secondary, dependent source.

The neutral wire (generally color coded white I believe) is the 'return' leg for the 110 volt circuit. The idea is that the black 'hot' wire supplies current to the load and the white 'neutral' wire gives the current a return path to the breaker panel to complete the circuit. Of course that's rubbish since with AC current the direction of the current is constantly changing 60 times every second. So every 1/30th of a second the white wire is the (positive) 'hot' one. The real physical difference between the hot and the neutral wire is that, in a 110 volt circuit, the neutral wire connects to the ground bus in the breaker panel and the black hot wire connects to the hot bus. I believe the ground bus itself connects to two points. An actual Earth connection, like a copper or aluminum stake actually pounded into the ground and a center tap connection from the distribution transformer at the street. So the ground bus basically serves two purposes. A connection that allows for 110 volts from a 240 volt secondary winding and a safety connection directly to Earth to reduce shock hazards.

Both the white neutral wire and the green ground wire are connected to the ground bus in the breaker panel. The difference is at the other end. The neutral wire connects to one side of the load and carries the current under normal operation of the device. The green wire just connects to whatever part of the device the manufacturer wants to keep at ground potential. If the metal case ends up with a voltage the ground wire will give the electrons a path straight to ground along a copper wire with a much lower resistance than a human body. Since the human body, even wet, has a much higher resistance than a copper wire most of the current will flow through the wire instead of the human.

Note that on a 240 volt load the white wire actually also connects to the hot bus. Well there are actually two hot buses in a panel representing two legs of a center tapped transformer. In that case I believe only the ground wire connects to the ground bus. So for 240 volt circuits there really is no neutral wire. Just two hot wires and an earth/ground connection.

 

[cmb]

with AC current the direction of the current is constantly changing 60 times every second. So every 1/30th of a second the white wire is the (positive) 'hot' one.

Very confusing/confused here. (Notwithstanding the 1/30th sec typo) Why you associate +ve with 'hot' I am unclear. What counts is the work that can be done per Coulomb of charge (viz. volts - and for mains that is with respect to the neutral). It matters not if it is + or -.

In polyphase AC circuits, the neutral is the line back to the star point of the polyphases. This is usually earthed at the distribution, so, nominally, the neutral line should be at ground potential. It is therefore never 'hot' (whatever that means), unless you also regard the whole of the Planet Earth becoming 'hot'.

The reason the neutral is not always at the potential of where it is earthed (i.e. why it is not always at ground potential) is if there is a fault current from the live lines running into ground. If this happens, then effectively the circuit will then push the neutral line around. In this case, the neutral might become 'hot', but only in a fault condition. Usually, the neutral of a house ring circuit does, indeed, float around a few volts off Earth potential, just because of inductive effects, length of mains distribution trunks, &c., together with the fact that if each phase of the distribution is having different demands on it then there will likely be some deviation from ground for the neutral line.

In a RCD protection system, the neutral is attached via a relay to ground, so if neutral ends up floating away from ground for some reason by more than a few volts (to accommodate the usual effects, as above), the relay is activated and the circuit shuts down. It is set up like this because no current should be flowing from the live wire(s) straight to ground (thus pushing the neutral line away from ground reference), all live circuits should all route back to the star point of the polyphase distribution and NOT directly to ground [except in the fault condition].

I do not claim this is the setup for all international mains systems, I am sure somewhere in the world there are various permutations on such arrangements, but this should serve to describe basic principle.

 

[psparky]

Yes, I agree that the black hot is the hot. The neutral is never the hot...even for 1/30th of a second. Again, if you are holding the black wire (120V) in your hand with insulated boots in a dry condition...and you other hand is not completing the circuit...current doesn't flow. However, if you touch the neutral OR the ground with your other hand, current flows and you feel the shock.

Conversely, if you are holding the neutral wire and touch ground with your other hand, you will feel nothing. They are tied into the same bus bar in your panel. The potential voltage between them is zero!

 

[metiman]

Yes. cmb is correct. I was mistaken. Neutral = ground = center tap = safe. It is the same as the ground of a DC circuit. It can't hurt you unless you also touch a conductor with an electric potential above or below ground. Neutral is called neutral because it is always at 0 volts. Hot is called hot because it can hurt you (even burn you) if you touch it. By that definition both -170 volts and +170 volts are 'hot'.

Incidentally the 1/30th was not a typo but a dumb mistake. The current actually flows in one direction for half of a cycle which is half as much time (not twice as much time) or only 1/120th of a second. So the voltage waveform is between 0 and +170v for 1/120th of a second and between 0 and -170v for 1/120th of a second (assuming 120v rms), adding up to 1/60th of a second in total.

So to answer the OPs question the only difference between a ground wire and a neutral wire is what part of the load it connects to. The green 'ground' wire typically connects to the case of the device, and the white 'neutral' wire, which is also a ground wire, connects to the functional circuit or load. I guess another difference might be that the ground wire can connect to any Earth connection: a water pipe, a stake in the ground, but the neutral wire must (I think) connect to the ground bus in the breaker panel and then back to the center tap of the secondary winding.

 

[HORNETD]

This seams a little off topic for a physics forum but a few words of caution are in order so that the answers already given here do not cause someone an injury or worse. I have wired structures from Argentina to Alaska and from Malaysia to Uganda so I am aware that the explanations I am offering here are only applicable to North American practice and some of the other places were a Multi Grounded Neutral system is used for utility power distribution.

Many panel boards are not service equipment / customer service units. That is important because Service equipment is the only place were the "Grounded Current Carrying Conductor;" that most of us call the "Neutral;" is properly earthed or connected to ground. That is done by a conductor that is, in North American Practice, called the main bonding jumper. In panel boards that are not service equipment the Neutral is kept aloof from the "Equipment Grounding Conductor" or ground wire at all times.

The actual grounding / Earthing of the Service Equipment Enclosure is accomplished by connecting it to conductive materials that are buried in the Earth or are effectively functioning as if they are the earth, albeit on a much smaller scale. The Conductive materials that are buried in the Earth are called grounding electrodes. All of the grounding electrodes are deliberately bonded together to form the Grounding Electrode System. The conductor that connects the Service Equipment Enclosure to the Grounding Electrode System is called, strangely enough, the Grounding Electrode Conductor. I guess by that point in the code writing process the code officials were too tired to invent yet another obscure term but I digress. The purpose of Grounding or Earthing the Neutral is to "limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to Earth during normal operation."

The reason for all the specificity is to bring this to an important point. In any system that has Grounded Current Carrying Conductors the voltage drop caused by the normal flow of current in the grounded conductor will raise it's potential above that of the Earth / ground. Further if that "Neutral" becomes damaged or overloaded that voltage above ground can be at a level that is sufficient to cause injurious or destructive current to flow.

For all of these reasons Neutral conductors are not safe to come into contact with until all circuits of which they are a part have been deenergized, locked out and tagged out.

--
Tom

 

[jim hardy]

Nice job , Tom...

For us Joe Sixpacks,

the black wire is the one with smoke in it.

White wire should never be hot but it is not uncommon to find a 220 volt circuit wired with only a black and white white wire, both of them hot. In my book that's bad practice.
Sometimes a light switch is wired with a black and a white wire, and that's another place you may find a hot white wire.
So if in doubt check. And if not in doubt, still check anyway.

Now to original question -
neutral is a wire that returns current from a load, usually white in US house wiring.
ground is Earth or a wire connected to earth, usually green or bare in US house wiring..sometimes metal conduit serves that function.
In US house wiring they are connected to each other at the panel, or should be.

There is an unfortunate and widespread mis-use of the word "ground" to represent circuit common.
Circuit common may or may not be connected to Earth - consider a flashlight or airplane.

 

[psparky]

This seams a little off topic for a physics forum but a few words of caution are in order so that the answers already given here do not cause someone an injury or worse. I have wired structures from Argentina to Alaska and from Malaysia to Uganda so I am aware that the explanations I am offering here are only applicable to North American practice and some of the other places were a Multi Grounded Neutral system is used for utility power distribution.

Many panel boards are not service equipment / customer service units. That is important because Service equipment is the only place were the "Grounded Current Carrying Conductor;" that most of us call the "Neutral;" is properly earthed or connected to ground. That is done by a conductor that is, in North American Practice, called the main bonding jumper. In panel boards that are not service equipment the Neutral is kept aloof from the "Equipment Grounding Conductor" or ground wire at all times.

The actual grounding / Earthing of the Service Equipment Enclosure is accomplished by connecting it to conductive materials that are buried in the Earth or are effectively functioning as if they are the earth, albeit on a much smaller scale. The Conductive materials that are buried in the Earth are called grounding electrodes. All of the grounding electrodes are deliberately bonded together to form the Grounding Electrode System. The conductor that connects the Service Equipment Enclosure to the Grounding Electrode System is called, strangely enough, the Grounding Electrode Conductor. I guess by that point in the code writing process the code officials were too tired to invent yet another obscure term but I digress. The purpose of Grounding or Earthing the Neutral is to "limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to Earth during normal operation."

The reason for all the specificity is to bring this to an important point. In any system that has Grounded Current Carrying Conductors the voltage drop caused by the normal flow of current in the grounded conductor will raise it's potential above that of the Earth / ground. Further if that "Neutral" becomes damaged or overloaded that voltage above ground can be at a level that is sufficient to cause injurious or destructive current to flow.

For all of these reasons Neutral conductors are not safe to come into contact with until all circuits of which they are a part have been deenergized, locked out and tagged out.

--
Tom

You ever notice that in almost thread there is someone who has no idea what they are talking about, someone who has some idea, someone who has a pretty good idea what they are talking about, someone who really knows what they are talking about...and then lastly, someone who knows EXACTLY what they are talking about.

Pretty cool...all part of the learning process. Also, when the "EXACTLY" guy speaks up...the thread is typcially over. Good stuff.

 

[metiman]

neutral is a wire that returns current from a load

Does the hot wire not also 'return' current from load? I don't like the use of 'return' in this context as it seems to imply a direction, but there is no direction in AC. The electrons (or electric field) are just oscillating/vibrating in place. The 'hot' conductor connects between an electric potential which is either higher or lower than ground potential. The neutral conductor connects between ground potential and the load.

 

[cmb]

Does the hot wire not also 'return' current from load? I don't like the use of 'return' in this context as it seems to imply a direction, but there is no direction in AC.

But there is certainly asymmetry. The return goes to the star point that is nominally zero net charge. The 'hot' wire pulls charge from that net neutral point, then pushes it back. The 'hot' wire has a continually fluctuating level of charge on it, first one way, then the other. The 'return' wire is the return route for either the electrons that the hot wire is pushing out, or [arguably] the 'holes' that the hot wire is pushing 'out'. Just terminology.

 

[psparky]

Don't forget that the nuetral comes from a centertapped transformer.

The USA house panel has two legs...one vector at 120 volts...and one vector at -120 volts.

Voltage is the DIFFERENCE between two points. In this case 120 - (-120) = 240 volts. And yes they are rotating vectors, but will always be 180 degrees apart and will always deliver 240 volts when line to line.

The center tap just takes the one side...120 - 0 = 120 Volts. The center taps are always grounded at the transformer and panel...even in three phase.

The the common (center tap) is just "shortcutting" the normal voltage...1/2 in the case of house panels...and a factor of 1.73 (square root of three) in three phase.

So the neutrals are derived from the hots...and are grounded.

Just another way to look at it.

 

[cmb]

Don't forget that the nuetral comes from a centertapped transformer.

The USA house panel has two legs...one vector at 120 volts...and one vector at -120 volts.

Voltage is the DIFFERENCE between two points. In this case 120 - (-120) = 240 volts. And yes they are rotating vectors, but will always be 180 degrees apart and will always deliver 240 volts when line to line.

Sounds like you are describing a 2 phase system. Does USA really have 2 phase domestic supply at the distribution panel? How/where does it convert from 3 phase?

 

[psparky]

Sounds like you are describing a 2 phase system. Does USA really have 2 phase domestic supply at the distribution panel? How/where does it convert from 3 phase?

Absolutely. USA does only have line to line single phase in residential panels. I'm not sure I would use the term "two phase"...as this can lead to confusion...but I know what you mean. The transformers located every so often down streets grab to hots (line to line single phase) from the three phase lines above and convert to 240 volt. The transformer also has a center tap or neutral...also called common which is where most of the homes are powered by 120 volt. These 120 volt loads are line to neutral. I think each transformer is only like 15KVA...so that feeds roughly 6 houses or so.

Only big ticked items in residential get the 240 volt...such as air conditioners, dryers, ovens...etc.

There are two separate bus bars in a USA residential panel...line 1 and line 2. There is a neutral bar as well with the ground tied out of it as discussed above. So your loads can only be hooked up with a 2 pole (240 volt) or single pole (120 volt) breaker.

Three phase is used in all commercial and industrial applications USA though. All the power lines and generators are definitely three phase.

 

[Averagesupernova]

Sounds like you are describing a 2 phase system. Does USA really have 2 phase domestic supply at the distribution panel? How/where does it convert from 3 phase?

He is NOT describing 2 phase. It is split-phase, which is still technically single phase.
-
Edit: Hmmmm, posted at exactly the same time as psparky.

 

[psparky]

He is NOT describing 2 phase. It is split-phase, which is still technically single phase.
-
Edit: Hmmmm, posted at exactly the same time as psparky.

It's sort of right by saying two phase because you have two different vectors sitting at 180 degrees apart.

However, whether you are line to line...or line to neutral...there is only one sinusoid produced through the load...aka...single phase.

Only a three phase system (3 pole breaker) will produce true multi-phasing...on planet Earth anyways.

 

[HORNETD]

Absolutely. USA does only have line to line single phase in residential panels. I'm not sure I would use the term "two phase"...as this can lead to confusion...but I know what you mean. The transformers located every so often down streets grab to hots (line to line single phase) from the three phase lines above and convert to 240 volt. The transformer also has a center tap or neutral...also called common which is where most of the homes are powered by 120 volt. These 120 volt loads are line to neutral. I think each transformer is only like 15KVA...so that feeds roughly 6 houses or so.

Not quite. In most of North America the practice is the transformers are supplied by a Multi Grounded Neutral (MGN) distribution system. Each transformer is supplied by a single phase conductor and a neutral conductor. The neutral conductor at one end of the primary winding is common to the center tap of the transformer's secondary winding. Each transformers' neutral connection is grounded at the transformer. The neutral conductor is also grounded at intervals along the line if the distance between transformers is greater such as is true in rural areas. The neutral conductor is also grounded at each premise served through a grounding electrode conductor that connects the neutral conductor to the Grounding Electrode System. All of that is done in order to "limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to Earth during normal operation." A cross between the distribution lines and the secondary service conductors will cause the circuit protection equipment to open because the transformer secondary winding will not offer enough impedance to the fault current to prevent the protectors from opening. If the cross is directly to the neutral the protectors will open even faster as the current will rise even more quickly since the protector mechanism will sense that condition as a fault rather than an overload.

I do realize that these ideas can be clear as mud at times. That is why it is called work. If it were easy they would hire our kids to do it.

--
Tom

 

[HORNETD]

Sounds like you are describing a 2 phase system. Does USA really have 2 phase domestic supply at the distribution panel? How/where does it convert from 3 phase?

No it is definitely single phase. To call it two phase you would be alleging that a multi phase system can be created just by tapping a single transformer secondary winding that is magnetically coupled to a single phase primary winding. If that were in fact true than you could create any number of phases you desired by multi tapping a single transformer winding.

--
Tom

 

[cmb]

No it is definitely single phase. To call it two phase you would be alleging that a multi phase system can be created just by tapping a single transformer secondary winding that is magnetically coupled to a single phase primary winding. If that were in fact true than you could create any number of phases you desired by multi tapping a single transformer winding.

--
Tom

I don't see what you are saying.

A 'neutral' is a line with [nominally] constant charge on it (hopefully 'net neutral charge', if earthed).

A 'hot' AC line is one with periodic time-varying charge on it.

Two phases are two lines with periodic time-varying charge on them, but of different phase angles.

A two phase system is one with two lines with periodic time-varying charge on them at 180 degree apart. You get this from one phase feeding into a transformer with a grounded centre-tap secondary. The two outputs will be at 180 deg out of phase = two phase.

No, you cannot tap any old number of phases off a simple transformer. If you feed one phase in, you get one phase out of one winding, or two phases out of two windings which might be 180 translated.

 

[pawprint]

From a very practical point of view it should be remembered that Earth (or ground) varies a little from place to place. Electronic circutry can be badly affected by this. In any large electronic instalation (e.g. a building-wide audio or CCTV system, or even an audio mixing panel) every unit must be run back, usually by the coaxial cable shielding, to a common 'earth point' to avoid noise.

 

[psparky]

I don't see what you are saying.

A 'neutral' is a line with [nominally] constant charge on it (hopefully 'net neutral charge', if earthed).

A 'hot' AC line is one with periodic time-varying charge on it.

Two phases are two lines with periodic time-varying charge on them, but of different phase angles.

A two phase system is one with two lines with periodic time-varying charge on them at 180 degree apart. You get this from one phase feeding into a transformer with a grounded centre-tap secondary. The two outputs will be at 180 deg out of phase = two phase.

No, you cannot tap any old number of phases off a simple transformer. If you feed one phase in, you get one phase out of one winding, or two phases out of two windings which might be 180 translated.

It's really an age old argument. You are certainly not wrong in what you are saying.

But you would agree that when you put a line to neutral across a load...you do get one single phase Sin wave...and one Single phase current wave?

As long as you agree with that...you can say whatever you want in my mind.

 

[Averagesupernova]

It is SINGLE PHASE! I emphasize this so much since there is actually a system that is two phase. The phases are 90 degrees apart. There needs to be a differentiation between the two, so I will rant and rave until it is realized.

 

[psparky]

It is SINGLE PHASE! I emphasize this so much since there is actually a system that is two phase. The phases are 90 degrees apart. There needs to be a differentiation between the two, so I will rant and rave until it is realized.

I agree with you...but CMB is a pretty smart guy...so I don't want to discount his opinion.

Tell me about this two phase system. Two vectors 90 degrees apart. When line to line or line to neutral...don't they still just make single phase?

 

[Averagesupernova]

A single pair of conductors is always just a single phase. It takes at least three conductors to get more than one phase. So I guess I don't understand your question.

 

[cmb]

It is SINGLE PHASE! I emphasize this so much since there is actually a system that is two phase. The phases are 90 degrees apart. There needs to be a differentiation between the two, so I will rant and rave until it is realized.

You can call that a 2-phase system if you like, but please let me know; what is the phase angle between the four phases in a 4-phase system?

 

[cmb]

It's really an age old argument. You are certainly not wrong in what you are saying.

But you would agree that when you put a line to neutral across a load...you do get one single phase Sin wave...and one Single phase current wave?

As long as you agree with that...you can say whatever you want in my mind.

Absolutely - the two hot lines of a 2 phase system together = 1 phase. However, the point to note is that the average absolute voltage at any moment in time of the two lines should be zero (wrt the neutral/earth). This is essentially the defining point of a poly-phase system - the potentials of all the lines will sum to zero at any given moment of time. As a result, the 'earth' can be used as a 'virtual' return line for all the phases together.

This is quite different to a single line (single, or out of any number of phases) in which the average voltage between the two lines varies wrt neutral/ground.

 

[psparky]

You can call that a 2-phase system if you like, but please let me know; what is the phase angle between the four phases in a 4-phase system?

That's what I'm trying to say...you're "2 phase" system at 90 degrees is no different than the "2 phase" system at 180 degrees.

They both produce a single phase sinusoid across a load.

I would agree that a 4 phase system is a 4 phase. 4 different sinusoids.

 

[Averagesupernova]

As far as I know there is no such thing as a 4-phase system. If you want to call 2-phase 90 degree system 4-phase because you can center tap the transformers then I guess, but you know my feelings on this. You could call our 3-phase system 6-phase by doing the same thing but again I call B.S.

 

[psparky]

Absolutely - the two hot lines of a 2 phase system together = 1 phase. However, the point to note is that the average absolute voltage of the two lines would be zero (wrt the neutral/earth).

Yes, the DC is zero. Agreed.

However, the RMS is what counts.

 

[psparky]

As far as I know there is no such thing as a 4-phase system. If you want to call 2-phase 4-phase because you can center tap the transformers then I guess, but you know my feelings on this. You could call our 3-phase system 6-phase by doing the same thing but again I call B.S.

Things don't have to be three phase. They could have made the generators 9 phase if they wanted to. With 9 phase motors as loads...etc.

They just figured that 3 phase would do the best for the money involved.

But certainly...a bigger than 3 phase system can exist. Does it typically exist? No.

 

[Averagesupernova]

This is nuts. There is a good reason it is called what it is to avoid confusion between one system and the other. The basis is this: If you can take any pair of wires in a system and compare the phase of another pair (one wire being common between pairs is permitted) and come up with something other than 180 degrees out of 0 degrees out then it is more than single phase. Until then, SINGLE PHASE!

 

[psparky]

This is nuts. There is a good reason it is called what it is to avoid confusion between one system and the other. The basis is this: If you can take any pair of wires in a system and compare the phase of another pair (one wire being common between pairs is permitted) and come up with something other than 180 degrees out of 0 degrees out then it is more than single phase. Until then, SINGLE PHASE!

Again. I agree.

3 phase (line to line to line) or higher is multiphase.

Line to line to neutral is not three phase. It's two different voltages being delivered to two different loads. An electric oven is a good example. Line to line for heat...line to neutral for control. Two single phase systems.

 

[cmb]

This is nuts. There is a good reason it is called what it is to avoid confusion between one system and the other. The basis is this: If you can take any pair of wires in a system and compare the phase of another pair (one wire being common between pairs is permitted) and come up with something other than 180 degrees out of 0 degrees out then it is more than single phase. Until then, SINGLE PHASE!

If you are saying that convention has called two lines out of phase by 180 'single phase', three lines out of phase by 120 '3-phase' and 4 lines 90 out of phase '2-phase' then there's nothing much I can say logically about that! I'm not saying you are wrong, it just doesn't make much sense.

360°/1 = 1 phase
360°/2 = 1 phase
360°/3 = 3 phase
360°/4 = 2 phase
?

Well... so much for conventions...

 

[Averagesupernova]

If you are saying that convention has called two lines out of phase by 180 'single phase', three lines out of phase by 120 '3-phase' and 4 lines 90 out of phase '2-phase' then there's nothing much I can say logically about that! I'm not saying you are wrong, it just doesn't make much sense.

360°/1 = 1 phase
360°/2 = 1 phase
360°/3 = 3 phase
360°/4 = 2 phase
?

Well... so much for conventions...

First of all, you cannot have 2 lines 180 degrees out of phase. Phase is relative. You don't have enough conductors to make that claim. So I think what I have quoted in this post is out the window. You can try again though with different wording so we can work towards a resolution. :)

 

[psparky]

If you are saying that convention has called two lines out of phase by 180 'single phase', three lines out of phase by 120 '3-phase' and 4 lines 90 out of phase '2-phase' then there's nothing much I can say logically about that! I'm not saying you are wrong, it just doesn't make much sense.

360°/1 = 1 phase
360°/2 = 1 phase
360°/3 = 3 phase
360°/4 = 2 phase
?

Well... so much for conventions...

360/4=4 phase
360/5=5 phase
360/6=6 phase...etc.

If a electric motor builder gets bored and decides to build a 9 phase generator...he can do that. He can also build a 9 phase motor for it to run off of. The 9 phase generator will have 9 line to line conductors and one ground. If he wants to have a neutral he can. But he doesn't have to.

This is 360/9...aka 9 phase! 9 vectors 40 degrees apart. Single phase will never exist in this system unless you only utilitize two conductors.

 

[cmb]

First of all, you cannot have 2 lines 180 degrees out of phase. Phase is relative. You don't have enough conductors to make that claim. So I think what I have quoted in this post is out the window. You can try again though with different wording so we can work towards a resolution. :)

The origin of this came from post #25. I asked whether the system described was a '2-phase' system - consisting of two lines, one at -120V while the other was at +120V with respect to a third line, the neutral return. If I had one neutral and one sinusoid, I'd definitely call that 1 phase. But it seems to me that if you stick that into a transformer and centre tap the secondary, you then end up with the scenario described in #25. Three lines total, a neutral and two phase lines 180 opposed.

I have just taken a look at my site transformer, which are set up in exactly this way. It has a 'single phase' transformer in it where the secondary is centre tapped to ground (it means you only get ~75V away from ground at anyone time on either of the two lines, but you get the 110V RMS voltage enough to run your kit (this reduces risk of shock on work site because your kit never gets more than that 75V from ground)). It even says on it "2P + E"! What is "2P"?

 

[psparky]

The origin of this came from post #25. I asked whether the system described was a '2-phase' system - consisting of two lines, one at -120V while the other was at +120V with respect to a third line, the neutral return. If I had one neutral and one sinusoid, I'd definitely call that 1 phase. But it seems to me that if you stick that into a transformer and centre tap the secondary, you then end up with the scenario described in #25. Three lines total, a neutral and two phase lines 180 opposed.

I have just taken a look at my site transformer, which are set up in exactly this way. It has a 'single phase' transformer in it where the secondary is centre tapped to ground (it means you only get ~75V away from ground at anyone time on either of the two lines, but you get the 110V RMS voltage enough to run your kit (this reduces risk of shock on work site because your kit never gets more than that 75V from ground)). It even says on it "2P + E"! What is "2P"?

2P = 2 pole...aka...single phase...lol