Quick question - Reg number prohibiting SP RCBOs on TT

[JohnW2]

The crucial point (and I'm not sure if you have yet acknowledged it) is that the phase difference of two currents, unlike two voltages, does not depend on any third 'reference' - one can merely 'cut into' the circuit at the two points of interest and compare the time course of the two currents ones sees, without reference to anything else.

But if you were to measure the voltage between those two points you would find that there was one, otherwise there would be no current. If there is current flowing between two points there must be a potential difference between those two points, and you do not need a 3rd point.

Yes, indeed - and, with the scenario I was discussing, the pd between those two points would be in phase with the (in phase) currents being measured at (and between) those two points (as must be the case with resistive loads) ... but what does any of that prove?

Kind Regards, John.

 

[ban-all-sheds]

The voltage waveforms aren't out of phase when measured across each half of the load individually based upon a single, in-phase current through each resistance.

They are when you reference them to their common point.

For a 110V CTE supply, if you use the centre-tap as your reference, then yes, the voltages on each live leg will be 180º out of phase which each other.

And for page after page after page I have been telling you that that is what I'm doing - using the centre point as the reference.

Why?

Because if presented with something described as 2-phase 3-wire, there has got to be a common point of reference as you can't get 2 phases out of 3 wires unless they share one. So given that we would expect any polyphase system to have phases with non-zero phase angles which would be more logical for something described as 2-phase 3-wire - sharing a point which got 2 phases with 0° and two different voltages, or sharing a point which got 2 phases with a non-zero angle and the same voltages?

It would be really good if you could forget all your history of something called split phase and imagine this system being totally new to you. How would you use the 3 wires to get 2 phases?

Now add your neutral between the junction of R1/R2 and the c.t. of the xfmr. If R1=R2 then no current flows in the neutral. Neither I1 nor I2 change in magnitude nor in their relationship to each other, nor does the polarity of the p.d. across each resistance change. Agreed?

No, absolutely and fundamentally disagree because of the meaning of the centre point when you call it a 2-phase 3-wire system, as per above.

As soon as you introduce that common point, and designate it 2-phase, you stop measuring everything from one end point to the other and start measuring from the centre to each end point.

So taking the first half of the cycle when the top is + wrt to the bottom, it is also + wrt to the centre.

But the bottom is not + wrt the centre it is -

So with conventional current flow, there is current from the top to the centre and from the centre to the bottom.

So in one half the current is flowing from L1 to N and in the other it is flowing from N to L2.

Different directions. Out of phase by 180°.

So the phase relationship of voltage to current in each half of the load taken individually is exactly the same as it was before you added the neutral connection.

True, because the voltage changes direction at the same time. L1 is + wrt N, L2 is -.

No current has changed direction or changed its phase relationship to another current. No p.d. across a load, or a part of a load has changed in voltage, polarity, or phase relationship either. Yes?

No.

From the perspective of N, one L is +, the other is -, they are not both + or both -.

From the perspective of N one current is flowing one way and the other is flowing the other way. Just like if you were standing on a roundabout looking up one road, and all the cars were driving along one side of the road, round the roundabout and back up the other side of the road, when you looked at the road you would say that the cars were going in two directions, towards you and away from you. They might all be going from one car par to another, and an observer whose point of reference was one car park would say "they are all going in one direction, from here to there". But that is not what the person whose reference point is the roundabout sees.

As soon as you have something which you call 2-phase 3-wire the only logical way to organise your points of reference is that you have a common N and between that common point and the other two you have two voltages, alternating in polarity, and at any time apart from zero-crossing one point is + wrt to N and the other is -. They are never both + or both -.

Between that common point and the other two you have two currents, alternating in polarity, and at any time apart from zero-crossing one current is flowing one way (away from N) and the other is flowing the other way (towards N). They are never both flowing towards N or both flowing away from it.

 

[ban-all-sheds]

Yes, indeed - and, with the scenario I was discussing, the pd between those two points would be in phase with the (in phase) currents being measured at (and between) those two points (as must be the case with resistive loads) ... but what does any of that prove?

It shows that whatever frame(s) of reference you use they must be consistent, and that you need more than one point for current to flow and that there must be a pd between them.

Again - forget all previous involvement with something called split-phase.

If you were presented with something which you were told was 2-phase 3-wire, would you expect it to have been provided so that you had access to two phases with a zero degree angle and one twice the magnitude of the other?

 

[bernardgreen]

If you were presented with something which you were told was 2-phase 3-wire, would you expect it to have been provided so that you had access to two phases with a zero degree angle and one twice the magnitude of the other?

I would not "expect" to be anything. I would ask exactly what it was.

 

[JohnW2]

If you were presented with something which you were told was 2-phase 3-wire, would you expect it to have been provided so that you had access to two phases with a zero degree angle and one twice the magnitude of the other?

That is a totally different, and totally new, question. There are countless examples of officially-created and/or widely-established terminology and jatgon which do not correspond to my 'expectations', but I have little choice but to live with them.

Kind Regards, John.

 

[ban-all-sheds]

If you were presented with something which you were told was 2-phase 3-wire, would you expect it to have been provided so that you had access to two phases with a zero degree angle and one twice the magnitude of the other?

I would not "expect" to be anything. I would ask exactly what it was.

OK - let's say you can't ask. You've been given this box with 3 terminals on it and you are told that it's 2-phase 3-wire. You have a bunch of test instruments. You establish that there is xV between A & B, xV between A&C and 2xV between B&C.

Which would you think was the most logical way to view what the box, described to you as 2-phase 3-wire?

"It provides xV between A&B and xV between A&C, and there are 2 different phases."

Or

"It provides xV between B&A and 2xV between B&C and there is only 1 phase."

?

 

[ban-all-sheds]

That is a totally different, and totally new, question.

OK, fine.

Can you answer it, and be reasonable?

 

[JohnW2]

That is a totally different, and totally new, question.

OK, fine. Can you answer it, and be reasonable?

Although your question seemed almost rhetorical, I thought I had probably implicitly answered it, anyway.

Anyway, to be explicit and tell you what you must already understand - no, I obviously would not 'expect' the phrase to have the meaning you indicated. However, as I said/implied, if I had to get into 8+ page discussions about every bit of electrical teminology/jargon which did not correspond my 'expectations' on the basis of the word(s), I (and probably others) would probably die of boredom.

I would add that this new question you have posed almost makes me wonder what side of this argument you are now on - it almost seems as if you have two Devil's Advocates doing battle in your brain!

Kind Regards, John.

 

[bernardgreen]

"It provides xV between B&A and 2xV between B&C and there is only 1 phase."

Is the closest answer from those you offer.

I would say it was a single phase supply at 2xV with a voltage divider of some sort connected to A ( the apparent mid-point ). That is all I can tell from voltage readings. The voltage divider could be a pair of high impedance resistors in series between B and C, it could be a inductive coil across B and C with a centre tap connected to A, it could be anything.

If I was able to add known loads between A and B and between A and C it would be possible to work out the impedance of the midpoint and then make a reasonable assessment of what was connected between A B and C.

 

[ban-all-sheds]

Anyway, to be explicit and tell you what you must already understand - no, I obviously would not 'expect' the phrase to have the meaning you indicated.

Neither would I.

Nor, I suspect, would the IET expect people to interpret it that way.

I would add that this new question you have posed almost makes me wonder what side of this argument you are now on - it almost seems as if you have two Devil's Advocates doing battle in your brain!

The more I thought about it the more I came to see that there is such a thing as a 2-phase 3-wire supply, there is a way (the most reasonable way) to look at it which gives you a non-zero phase angle and that the IET are not wrong in their terminology. Maybe there are people here who have greater knowledge of electrical engineering theory than the collective IET/BSI JPEL/64 committeee, but I am not one of those.

 

[ban-all-sheds]

"It provides xV between B&A and 2xV between B&C and there is only 1 phase."

Is the closest answer from those you offer.

So when you've been told it's a 2-phase supply you would interpret your test results in a "no it's a single phase supply at two different voltages" way.

OK.

What if the two voltages you'd measured had been 240 & 415?

 

[Tech99]

The voltage waveforms aren't out of phase when measured across each half of the load individually based upon a single, in-phase current through each resistance.

They are when you reference them to their common point.

If you select three points at random along any conductor in which AC is flowing, then choose the middle one of those three as your reference, the voltages at the other two will appear out of phase.

Go back to the circuit I described above to the point before we added the neutral, so it's just R1 & R2 in series across the full secondary winding. It's a simple 2 wire circuit with only one current path so it can't be anything but single phase, agreed?

Now select the point between R1 & R2 as your reference and compare the voltages appearing at the top of R1 and the bottom of R2. They'll be 180 out of phase, because you're using a point between them as your reference. But it isn't a 2-phase arrangement, is it?

Because if presented with something described as 2-phase 3-wire, there has got to be a common point of reference as you can't get 2 phases out of 3 wires unless they share one. So given that we would expect any polyphase system to have phases with non-zero phase angles which would be more logical for something described as 2-phase 3-wire - sharing a point which got 2 phases with 0° and two different voltages, or sharing a point which got 2 phases with a non-zero angle and the same voltages?

You're hung up on whether you can see voltages which are out of phase with each other compared to a common reference point. You need to look at it from the point of view of how many currents of a different phase (relative to each other) you can get by connecting across different combinations of supply wires.

Now add your neutral between the junction of R1/R2 and the c.t. of the xfmr. If R1=R2 then no current flows in the neutral. Neither I1 nor I2 change in magnitude nor in their relationship to each other, nor does the polarity of the p.d. across each resistance change. Agreed?

No, absolutely and fundamentally disagree because of the meaning of the centre point when you call it a 2-phase 3-wire system, as per above.

So you think when connecting a third wire between the common point of R1/R2 and the xfmr c.t. in which no current flows because R1=R2 that the voltages across the loads and/or the currents through them somehow change in direction or relationship to each other? How do you think that happens when the third wire has merely connected points together which are already at the same potential so that no current actually flows in that third wire?

As soon as you introduce that common point, and designate it 2-phase, you stop measuring everything from one end point to the other and start measuring from the centre to each end point.

Why? What do you think is so special about the centre point of the transformer, taking the system as a whole? Because it's the supply wire designated as neutral? Because it's the point which is earthed? What exactly?

If the c.t. is earthed but not extended as a neutral, as with 110V CTE site tool supplies, do you still think that should be called 2 phase because there are two voltages at the ends of the winding which are 180 out of phase relative to earth?

But the bottom is not + wrt the centre it is -

In any secondary winding one end will be +ve and the other -ve at any given instant relative to some point mid way. It has to be because the current is flowing in one given direction through the whole length of the winding at any given moment. The simple 2-wire 240V secondary on that rural pole xfmr feeding one house is no exception - Select a mid point and on any given half cycle one end will be +ve with respect to it and the other -ve (with one end of the winding earthed then obviously the midpoint will also be changing its polarity with respect to earth on each half cycle, but it doesn't alter the fact that on any half cycle one end of the winding will still be +ve and the other -ve with respect to the mid point).

So with conventional current flow, there is current from the top to the centre and from the centre to the bottom.

With the top end of the winding +ve and bottom -ve, conventional current flow within the winding will actually be from bottom to top. It's the source.

So in one half the current is flowing from L1 to N and in the other it is flowing from N to L2.

If we're taking L1 as being the top and L2 the bottom, then within the xfmr secondary current will be flowing L2 to N and N to L1. However -

Different directions. Out of phase by 180°.

That isn't different directions. The current is flowing in one direction through the whole winding from L2 to L1, passing N on the way. Yes, at the precise point of the winding at which N is connected the current must obviously be arriving from the L2 side and departing toward L1. But if you select any point in a single conductor, whether a xfmr winding or just a piece of wire, the current must be arriving from one side and leaving via the other.

No current has changed direction or changed its phase relationship to another current. No p.d. across a load, or a part of a load has changed in voltage, polarity, or phase relationship either. Yes?

No.

You agree that with R1=R2 no current flows through the neutral wire which has been added? So how can any of the voltages and currents which existed before have changed?

From the perspective of N, one L is +, the other is -, they are not both + or both -.

From the perspective of N one current is flowing one way and the other is flowing the other way.

From the perspective of the xfmr c.t. point that was happening before we added the neutral wire.

 

[Tech99]

"It provides xV between B&A and 2xV between B&C and there is only 1 phase."

Is the closest answer from those you offer.

I would say it was a single phase supply at 2xV with a voltage divider of some sort connected to A ( the apparent mid-point ). That is all I can tell from voltage readings. The voltage divider could be a pair of high impedance resistors in series between B and C, it could be a inductive coil across B and C with a centre tap connected to A, it could be anything.

If I was able to add known loads between A and B and between A and C it would be possible to work out the impedance of the midpoint and then make a reasonable assessment of what was connected between A B and C.

^^^^ This. The terminals could be connected directly to a c.t. xfmr with A on the centre tap. B & C could be connected to a winding with no tap and A to the midpoint of a resistive or capacitive divider which is across B & C. There are quite a few possibilities.

If you qualified it by saying that the terminals are connected solely to xfmr windings in some configuration with no resistors, coils, capacitors or other components involved, then given X volts A-B and A-C and 2X volts B-C it would be reasonable to conclude that the terminals are connected to a c.t. winding with A on the centre tap. Or it could be two separate xfmrs with windings connected appropriately and A at the common point between the secondaries. Or it could be even more transformers connected to give the same result. With only the voltage readings to go on, you couldn't tell.

 

[ban-all-sheds]

Now select the point between R1 & R2 as your reference and compare the voltages appearing at the top of R1 and the bottom of R2. They'll be 180 out of phase, because you're using a point between them as your reference. But it isn't a 2-phase arrangement, is it?

It is if you designate it as such and present it as something which provides two voltages with respect to a common point and those voltages are out of phase wrt the common point and therefore the currents flowing in loads wrt the common point are out of phase.

You're hung up on whether you can see voltages which are out of phase with each other compared to a common reference point. You need to look at it from the point of view of how many currents of a different phase (relative to each other) you can get by connecting across different combinations of supply wires.

Why do you?

Are you able to stop saying, in various ways "you just do", and point to an official definition or set of rules which shows that JPEL/64 really have got it wrong because their collective electrical engineering knowledge is inadequate?

So you think when connecting a third wire between the common point of R1/R2 and the xfmr c.t. in which no current flows because R1=R2 that the voltages across the loads and/or the currents through them somehow change in direction or relationship to each other? How do you think that happens when the third wire has merely connected points together which are already at the same potential so that no current actually flows in that third wire?

Simple question - when you look at the currents flowing in R1 and R2, with respect to their common point, are they out of phase?

Does the man standing on the roundabout see traffic going in two directions or one?

Why? What do you think is so special about the centre point of the transformer, taking the system as a whole? Because it's the supply wire designated as neutral? Because it's the point which is earthed? What exactly?

Because it is the common point of what is being presented as a 2-phase 3-wire supply.

Given that is is being presented and described as such, the only choices you have are:

1) To start observing, measuring and referencing the other two points wrt that centre point, because that is the only way the description makes sense

or

2) To say that you have more knowledge than the combined JPEL/64 and they are wrong.

Which is it to be?

 

[Tech99]

Are you able to stop saying, in various ways "you just do", and point to an official definition or set of rules which shows that JPEL/64 really have got it wrong because their collective electrical engineering knowledge is inadequate?

I don't know if the IEE/IET has any sort of official rules, but it has been accepted as a basic fact of electrical engineering for about the last 120+ years.

Simple question - when you look at the currents flowing in R1 and R2, with respect to their common point, are they out of phase?

No.

Does the man standing on the roundabout see traffic going in two directions or one?

He will see cars coming toward him, then pass and go away from him. Just as the current at the mid point between the two halves of the load must approach that mid point from one side and leave via the other.

To transpose your analogy to a railway, if you were standing on the platform at Rugby as the London-to-Liverpool express went through, then obviously the train would be approaching you from London direction, pass you at Rugby, then head away from you toward Liverpool.

But where did the train change direction? Before it got to Rugby it was travelling from London to Liverpool. After it passed you at Rugby it was still travelling from London to Liverpool. It didn't suddenly turn around and start going back towards London, did it? So it's still going in the same direction. And that's exactly what's happening with the current at the mid point of R1 & R2.

With apologies for the hastily drawn sketch:

You're suggesting that at point X on the diagram there are two currents which are out of phase with each other. How can that be when there is only a single current path around the circuit?

Given that is is being presented and described as such, the only choices you have are:

1) To start observing, measuring and referencing the other two points wrt that centre point, because that is the only way the description makes sense

That seems to be the problem. This new description doesn't make sense.

2) To say that you have more knowledge than the combined JPEL/64 and they are wrong.

Not just me. Every electrical engineer for over a century, and many more today who will continue to refer to it as a single phase system because that's what it is.