Why is residential wiring known as single phase?

[jim dungar]

Agreed. As a practical issue, viewing one leg as 180? out of phase with the other can be a very good thing.

Actually there are times when it is required (i.e. most power metering). But, there are also times when viewing a shift can be an issue (i.e. explaining why two windings of a single transformer behave differently when they are connected [X1->X2]+[x1->X2] versus [X1->X2]+[X2<-X1]).

 

[mivey]

Except I can never see his drawings for some reason

The idea is that parts of the circuit require positive pulses of energy at different points in time. With in-phase voltages, the positive pulses would occur at the same time and the circuit would not work. Thus the need for a source with 180? displaced voltages (or 30? for some of the circuits Besoeker has shown).

That is why the battery analogy does not work. The AC waveforms can give you positive pulses at 180? intervals but the battery can't. I tried in other threads to fix that by flipping the batteries at regular intervals but that went over some heads and did not prove useful.

 

[jim dungar]

The idea is that parts of the circuit require positive pulses of energy at different points in time. With in-phase voltages, the positive pulses would occur at the same time and the circuit would not work. Thus the need for a source with 180? displaced voltages (or 30? for some of the circuits Besoeker has shown).

The different pulses come from the connection of the rectifier, not because of a phase difference. You could rewire the rectifier components to work using one of the hot legs as a common.
I have shown how one of Besoeker's wiring diagrams supports my position that there is no phase difference.


How do we show a phase difference in this circuit? I know one method included 'different math techniques' when writing KCL formulas at nodes A, N, and B.

 

[jcormack]

Forgetting Power

Forgetting Power

Have not been on the forum for awhile - glad to see things remain the same. I remember similar threads in the late 90's.
I always like to point out that everyone talks about voltage and current independently. Measure the current in each leg! Measure the voltage from neutral ! Don't measure from neutral!

What about power? Voltage and current work together - the two represent energy -represent work. Power = Voltage X Current

Please compare the resultant power waveforms on both legs of a residential service (hint - negative X negative = positive)

I bet you find they are in phase.

 

[pfalcon]

The idea is that parts of the circuit require positive pulses of energy at different points in time. With in-phase voltages, the positive pulses would occur at the same time and the circuit would not work. Thus the need for a source with 180? displaced voltages (or 30? for some of the circuits Besoeker has shown).

That is why the battery analogy does not work. The AC waveforms can give you positive pulses at 180? intervals but the battery can't. I tried in other threads to fix that by flipping the batteries at regular intervals but that went over some heads and did not prove useful.

The different pulses come from the connection of the rectifier, not because of a phase difference. You could rewire the rectifier components to work using one of the hot legs as a common.
I have shown how one of Besoeker's wiring diagrams supports my position that there is no phase difference.
View attachment 6410

How do we show a phase difference in this circuit? I know one method included 'different math techniques' when writing KCL formulas at nodes A, N, and B.
View attachment 6411

Thanks for the drawings Jim. Maybe we can get you and Mivey on the same page now.

TECHNICALLY (at great need): 120/240 is a single-phase, single-phase-angle circuit. Which is where Jim is. Altering reference points, changing angles/phases/voltages and then resolving the math doesn't change this. It is what it is.

then since we can attach wires, meters, etc. to the circuit wherever we like AND since the typically residential setup provides the 240V with a standard voltage division at the half mark and that half mark is grounded

PRAGMATICALLY: We can immediately use this circuit as though it was +120, 0, -120 or 120<0, 0, 120<180. Howsoever you wish to express it. That except for some exceptional purposes we're not likely to encounter: We can ignore the literal technical physics of the circuit in favor of how we're going to use it (which is where Mivey is). And this is where Besoeker is designing things from.

An often underlooked part of this circuit is the inherent synchronization. As, technically speaking, they are a single waveform they are always synchronized. Whereas if we provided separate sources then special circuits would have to be added to keep them from getting out of sync.

Mivey and I had this massive discussion in another thread. It took awhile, but I no longer see any point where Mivey and I have any substantial disagreement.

 

[rbalex]

...

Please compare the resultant power waveforms on both legs of a residential service (hint - negative X negative = positive)

...

Yes, but is that the vector or scalar product? JK, (irrelevant)

This thread has gone on so long because too many people believe their own experience (emprical) trumps everyone and everything else. "WHAT I DO WORKS - I MUST BE RIGHT!!!!!!" :roll:

Sad thing is they are all quite smart - just stubborn.

 

[pfalcon]

Have not been on the forum for awhile - glad to see things remain the same. I remember similar threads in the late 90's.
I always like to point out that everyone talks about voltage and current independently. Measure the current in each leg! Measure the voltage from neutral ! Don't measure from neutral!
What about power? Voltage and current work together - the two represent energy -represent work. Power = Voltage X Current
Please compare the resultant power waveforms on both legs of a residential service (hint - negative X negative = positive)
I bet you find they are in phase.

Yes, but is that the vector or scalar product? JK, (irrelevant)
This thread has gone on so long because too many people believe their own experience (emprical) trumps everyone and everything else. "WHAT I DO WORKS - I MUST BE RIGHT!!!!!!" :roll:
Sad thing is they are all quite smart - just stubborn.

All so terribly complex for such a simple thing. This is a 240V circuit with a voltage divider at 120V: thereby it must all be of One phase and One angle because it is only One thing. No part of it can be the opposite of what it is. We reference the divider point to Zero. And amazingly enough we can now measure voltage both forward and backward giving us, from a pragmatic view, two voltages 180 degrees out of phase. It works. It's usable. And for all our purposes is indistinguishable from 120<0, 0, 120<180. All our designs and calculations work with the new point of reference. And because it is actually only One thing, the synchronization and other properties are inherently more stable than if they were separate sources.

 

[rattus]

Different phase angles would define that they're different phases. So yes, you really are saying there are two phases by declaring they have different phase angles.

Nonsense! Some mistakenly call the two legs of a residential service phases. Any extra phases must be provided by a separate generator. You can't deny if you observe V1n and V2n on a scope, you see different phase angles from a single phase transformer.

V1n and V2n are not defined relative to N. You don't have to measure them relative to N. Magicians make elephants appear to vanish, therefore it is. Wait. No. Appearance means nothing. Phase is phase. It is what it is. Not what you want it to be. Not what view you take of it. It is what it is.

The subscripts 1n and 2n mean V1 with respect to N and V2 with respect to N, therefore they must be measured with respect to N. If you measure them any other way, you are measuring something different. It can't be any clearer.

It actually does matter where they came from. I guarantee if you tried to set this up from separate transformer windings and tie them common you would get in trouble when you started to apply unbalanced loads. And V1n/V2n are not separate entities on heater elements. Therefore they can't be treated as such.

Maybe in practice, but not in the ideal case. I am making the point that the common winding should not be a factor in this discussion.

 

[T.M.Haja Sahib]

The instantaneous value is not a single number except at a single instant in time. Over time, it varies with respect to time as V_msin(ωt) in one winding and as V_msin(ωt+π) in the other when measured with respect to neutral.
The instantaneous value will be +120V twice during the positive half cycle at π/4 and 3π/4 and -120V at 5π/4 and 7π/4.

Correct.The instantaneous value changes from instant to instant.At one particular instant the voltage vector V1n is 120V and V2n is -120V.So what are the corresponding instantaneous currents in the hot conductors and neutral?Please answer it.

 

[John120/240]

Nonsense! Some mistakenly call the two legs of a residential service phases.

Interesting reading .......lots of it over my head. So what is the correct terminology for

two hots and one common or neutral ?

 

[jim dungar]

Interesting reading .......lots of it over my head. So what is the correct terminology for

two hots and one common or neutral ?

Single Phase.

or

MWBC

 

[rattus]

Interesting reading .......lots of it over my head. So what is the correct terminology for

two hots and one common or neutral ?

I would call L1 and L2 "legs". To call them "phases" implies a two-phase system which carries a separation of 90 degrees.

 

[T.M.Haja Sahib]

Can 120V single phase supply breed 180 degree phases?

Can 120V single phase supply breed 180 degree phases?

Yes.It can.If the sinusoid V1n is 120V,the sinusoid Vn1 is -120V.So even 120V single phase supply can breed 180 degree phases.But what is the use of it anyway?

 

[kwired]

I would call L1 and L2 "legs". To call them "phases" implies a two-phase system which carries a separation of 90 degrees.

Now we can go 100 more posts on "what is a leg?"

I kind of like what you said though. Most of the engineers don't understand simple things:happyyes:

 

[Besoeker]

Correct.The instantaneous value changes from instant to instant.At one particular instant the voltage vector V1n is 120V and V2n is -120V.So what are the corresponding instantaneous currents in the hot conductors and neutral?Please answer it.

Something, or nothing depending on the load - or lack thereof.
But I might be grossly mistaken.

Now, what's an instantaneous vector voltage?
Please answer it.

 

[T.M.Haja Sahib]

Now we can go 100 more posts on "what is a leg?"

Yes.We could.Our moderators are very nice and gullible.

 

[T.M.Haja Sahib]

Now we can go 100 more posts on "what is a leg?" <br>

Deleted due to repetition.

 

[Besoeker]

Yes.It can.If the sinusoid V1n is 120V,the sinusoid Vn1 is -120V.So even 120V single phase supply can breed 180 degree phases.But what is the use of it anyway?

But this is about 120-0-120. Not a 120V single-phase supply.

 

[Besoeker]

Yes.We could.Our moderators are very nice and gullible.

Please don't do that.
Personal insults are proscribed.

 

[Besoeker]

I would call L1 and L2 "legs". To call them "phases" implies a two-phase system which carries a separation of 90 degrees.

Well........
L1 is at +170V when L2 is at -170V wrt N at the same point in time. They cross zero at the same point in time but going in opposite directions.
I don't see how one can reasonably construe that as being in phase and, if not in phase, it must logically follow that they are out of phase and, if out of phase, it must logically follow that there is more than one phase.