What do you call this voltage

[leitmotif]

Are you talking Wye or Delta? For 480VAC Delta, leg to leg would be single phase 480VAC. When you add a neutral (which should be tied to ground per U.S. NEC), leg to neutral becomes 277VAC single phase. Just sketch out the vector diagram.

I believe you will find that 277 is derived from 480V 4 wire wye with centertapped neutral (generally bonded to ground per NEC in USA). Is one leg of 3 phase to the neutral.

I do not remember what a centertapped (between B and C) delta to opposite corner ie A(wild leg) voltage is on 480 - have not seen one of those hookups in years. On 240 delta I believe wild leg is 208 ?? - have not seen that in quite a while either.

Dan Bentler

 

[keithkyll]

...Using two wires of a 3-phase is not technically "single phase", ...

Yes it is.
Look out the back door at the wires on the pole. There's 3. That's 3 phases. That's all you get from the power company. Two of the 3 legs are used to send single phase to your house.
The center tap ground (neutral) is from a copper rod driven into the earth locally.

 

[RichWargo]

My bad. Leitmotif has the correct explanation. I didn't mean to imply center tapping the delta, it's the wye which has the center tapped neutral bonded to ground per NEC. And we get a fair number of jobs through our shop for which the customer is supplying 208VAC 3 phase. How they get it, I don't bother to ask. All I care is that it ups the panel price, due to the need to upsize components and wiring to handle larger current for same power.

Yes, Keithkyll is essentially correct, only minor disagreement is that only the two power legs come from the utility (actually from the pole mounted transformer), the third leg is from local ground. It's single phase, but split into two 120VAC legs with 240VAC available between the two power legs.

But my basic point was that it is essential to use common terminology, not make up your own because you think it's more correct.

 

[Fitz]

Sorry, but whether it makes more sense to you or not is not relevant. What is important is to follow conventional terminology.

Lighten up. I was only stating my opinion. I apologize for suggesting anything outside the boundaries of "conventional terminology".

 

[tomalbright]

Yes it is.
Look out the back door at the wires on the pole. There's 3. That's 3 phases. That's all you get from the power company. Two of the 3 legs are used to send single phase to your house.
The center tap ground (neutral) is from a copper rod driven into the earth locally.

Hrrrmmm.... haaaaw.... hmmm.,..

Well, YES, you are correct. IF you are using two wires from a pole transformer, then yes, "single phase" is correct. I think we will assume that it is done that way in most, if not all, cases.

 

[leitmotif]

Yes it is.
Look out the back door at the wires on the pole. There's 3. That's 3 phases. That's all you get from the power company. Two of the 3 legs are used to send single phase to your house.
The center tap ground (neutral) is from a copper rod driven into the earth locally.

If you are talking your house the three conductors on the service drop from the pole are Edison 3 wire.

Here is how it all works.
At the utility substation they bring in 3 phase.
Incoming is let us say 115,000 Volt phase to phase (primary distribution).
They will often reduce this to secondary distribution say 12,500 phase to phase 3 phase.

FOR COMMERCIAL
GOING OUT they go with the 12.5 to commercial at the service drop they put in a transformer 12.5 primary to say 480 secondary withe the secondary connected wye. They run a 4 conductor drop 3 hots and the common from all 3 phases (also called star point)
AT CUSTOMER SERVICE
3 phases are connected to the hots and the common to the neutral bus. The common can now be called the
neutral (GROUNDED CONDUCTOR) and is BONDED to the ground electrode system consisting of ground rods and or a water pipe. It is white or gray, at ground potential, carries current ie the imbalance between the phases.
This is also where the GROUNDING CONDUCTOR is derived. It is green, is at ground potential and normally carries no current

Both teh neutral white (GROUNDED) and ground (green) GROUNDING are often connected to the same bus ie neutral buss.

The three hots ie phases A B and C are often color coded in order Brown Orange Yellow between any two you will have 480.
Between any phase (Brown Orange or YEllow and the Neutral (GROUNDED Conductor) you will have 277.

Between neutral and ground you should have no potential but there may be some say 2 to 5 volt
and you should always have a fairly low resistance say 2 to 5 ohms.

The same is for 208 / 120 4 wire wye except the commonly colors for phases are Black Red Blue.

Now then for residential
SUBSTATION brings out two legs of 12,5 to the neighborhood. AT your house they put in the transformer with 12,5 primary and a 240 secondary. The secondary winding is centertapped (common) so that voltage from a leg of 240 to common is 120.
This is Edison 3 wire service.
AT RESIDENCE they bring in the 3 wires. Two connect to the hot bus these are often just black but we will do it right and make one black and other red. The common if done right is phase taped white at the mast head and in the panel. It is connected to the neutral bus. The neutral bus is connect to the ground grid - anything connected to neutral bus is at ground potential.
The neutral (GROUNDED) conductor is white current carrying. It will carry the imbalance of current between the two hots on a 240 load (dryer range etc) or will carry a current equal to the hot on a 120 load.
The ground (GROUNDING) green or bare or green with yellow stipe also connected to the neutral buss (in the main panel ONLY)

IN feeder panels fed by the main panel there is a separate bus for the neutral (GROUNDED current carrying white) this is floated ie not bonded to ground (ONLY in main panel) nor to the enclosure and another for the ground (GROUNDING) green etc non current carrying - this bus is bonded is bonded to the enclosure.

Dan Bentler

 

[tomalbright]

Well, I am being educated.

Here's a link to a wiki on single phase power.

This makes it TRUE that household voltage is single power, and actually, single phase is run via three wires on the distribution system. The "3 phases" we are talking about are for commercial or industrial applications.

Your mileage may vary, I have NO idea what the phasing is at my house, other than it is working very well!

 

[Jim Dungar]

Again people are using the slang term "phase" out of context and then trying to work backward to justify an explanation.

Single wires are not phases, they are "phase conductors".

You cannot have a voltage with a single reference point. A "phase voltage" can only be measured between two points. So it is actually incorrect to use the term voltage without saying what you are using for your reference points, like Line-Line or Line-Neutral.

It seems the most common use of "phase" means a single hot or line conductor, as opposed to a neutral or grounded conductor. Therefore, we (unknowingly?) actually refer to our voltage systems by the number of different Line-Line voltage combinations that are available irrespective of the presence or absence of a neutral reference.

2-phase systems actually exist, although they are archaic, just like 6-phase systems do. Just accept that 2-phase circuits have non-standard applications and therefore require non-standard formulas, do not try to use routine poly-phase methods to analyze them.

 

[leitmotif]

Jim
Guilty as charged. I think phase conductor is the term I was trying to remember - been so long sinnin with the slang I forgot the correct term.
Think I will look it up in NEC.
Will try to be more righteous in future.
Dan Bentler

 

[Jim Dungar]

Jim
Guilty as charged. I think phase conductor is the term I was trying to remember - been so long sinnin with the slang I forgot the correct term.
Think I will look it up in NEC.
Will try to be more righteous in future.
Dan Bentler

This is not an NEC item, it uses the terms ungrounded, gounded, neutral, and grounding conductors.

 

[Gilbert W]

Hmmmmm .... I'm probably wrong in my thinking, so please correct me if I don't get this right.

An electric current will be generated when a magnetic field passes through a piece of wire. The polarity at one end of the wire will be opposite from the other end. Basically 180 degrees apart. this pretty much describes a single phase generator. There is one North and one South magnetic pole and one winding.

A 3 phase generator has only one north and south pole also. What makes it different is that it has 3 windings that are 120 degrees apart. Each winding is generating a current that is 180 degrees apart at the 2 ends. Let's not connect the 3 sets of windings together yet. Each one is a single phase generator output. The output from any winding is 120 degrees different than the other 2 windings because it is mechanically located that way.

Phase A-B is 180 degrees apart

Phase B-C is 180 degrees apart and the sine wave starts 120 degrees after phase A-B

Phase C-A is 180 degrees apart and the sine wave starts 240 degrees after phase A-B


That's the way I try to look at it anyway.

 

[Jim Dungar]

Hmmmmm .... I'm probably wrong in my thinking, so please correct me if I don't get this right.

An electric current will be generated when a magnetic field passes through a piece of wire. The polarity at one end of the wire will be opposite from the other end. Basically 180 degrees apart. this pretty much describes a single phase generator. There is one North and one South magnetic pole and one winding.

You are describing the two ends of a single line as being out of phase with each other. This is not possible.

Choosing one end of a line as your reference point forces the other end to be in a single direction away from your reference point, but this is not a phase shift. Do you say the two terminals of a battery are 180° apart? If you have a 2-wire power supply and you call one terminal 0V, do you say the other terminal is 180° away?

 

[leitmotif]

Jim

IF the power suppy is the secondary of a control transformer
AND there is 120 VAC across the secondary
AND I connect a scope across the secondary what is the display on the scope?

NOW if I BOND one side of the secondary to ground will the scope display change and if so how?

ASSUMING the scope internal circuitry is not referanced to ground I do not think the displays will change and you will get a 60 Hz sine wave on the display. The peaks are 180 out of phase. All the scope will care about is the potential difference between the two secondary terminals.

If I referance the scope to ground then I think it will referance the sine wave to ground so the bottom of the curve is 0 and the other peak or side (?) is "line potential" ie 120 for a 120 V secondary. It will still be 60 Hz and 180 between peaks.

Now then for his single phase generator with no load connected the scope will read the same ie 60 Hz and peaks 180 out.

Dan Bentler

 

[Jim Dungar]

Jim

IF the power suppy is the secondary of a control transformer
AND there is 120 VAC across the secondary
AND I connect a scope across the secondary what is the display on the scope?

NOW if I BOND one side of the secondary to ground will the scope display change and if so how?

ASSUMING the scope internal circuitry is not referanced to ground I do not think the displays will change and you will get a 60 Hz sine wave on the display. The peaks are 180 out of phase. All the scope will care about is the potential difference between the two secondary terminals.

If I referance the scope to ground then I think it will referance the sine wave to ground so the bottom of the curve is 0 and the other peak or side (?) is "line potential" ie 120 for a 120 V secondary. It will still be 60 Hz and 180 between peaks.

Now then for his single phase generator with no load connected the scope will read the same ie 60 Hz and peaks 180 out.

Dan Bentler

Yes the opposite peaks of an alternating 60Hz waveform are 180 apart, but what does that have to do with the angular difference between the two ends of a straight line? How would you describe a single waveform as being "out of phase" with itself?

 

[Gilbert W]

Jim,



Sorry, I know a little, but I’m no expert on 3 phase systems. I’ve got some questions for you though.





So you’re saying that as the magnetic field passes through a wire as it does in a generator winding, the phase relationship between the ends of the wire is that they are in phase? Is that the correct terminology?







Previously you said, “Choosing one end of a line as your reference point forces the other end to be in a single direction away from your reference point, but this is not a phase shift.”



I was under the impression that the “other end” would swing both positive and negative and not just in a single direction, and if we are talking 60 Hz, the positive and negative peaks would be 8.3 mS apart. I was also under the impression that “choosing a reference point” shouldn’t “force the other end” to change in any way. Can you give me some insight on what exactly you meant?







I didn’t understand your comments about a battery or power supply either. I was under the impression that to have a phase relationship, at least one entity has to go “Full Circle” and return to it’s starting point on a consistent basis as the waveforms from a generator or transformer might do. I didn’t understand why you were using DC components in a discussion about AC phasing. Can you tell me why you used those examples and how they relate to AC phasing?





Thanks,

Gil