Quick question - Reg number prohibiting SP RCBOs on TT

[ban-all-sheds]

Eh? I thought the one thing on which we were all agreed (and, indeed, the whole basis of this discussion) is that there is one thing which has traditionally been called 'split phase' but which the IET now seem to want to call 2-phase 3-wire 180°. What on earth are these two things that you are postulating one might want/try to show were different?

One is the thing which has traditionally been called 'split phase' but which the IET now seem to want to call 2-phase 3-wire 180°.

The other is he thing you were thinking of when you wrote this:

In particular, if one used such a three wire supply by distributing the CT (as N) and one of the L's to various circuits in an installation, with unbalanced loads, I think it might perhaps be more logical (if one were inventing the terminoogy from scratch) to call that 2-phase.

I don't personally really give a jot what people want to call it, given that there is no ambiguity or safety issue.

You don't give the impression, to me at least, of someone who doesn't give a jot.

To the best of my knowledge, there is only one thing which 'split phase' can mean, and only one thing which 2-phase 3-wire 180° can mean

Do you believe that those are two different things?

If so, and you were presented with two sets of 3 terminals on a panel, unlabelled but arranged, say, in 2 inverted equilateral triangles, and an array of measuring devices of any sort you care to ask for, and you were told that one set of terminals was connected to a split phase supply, and the other to a 2-phase 3-wire 180° supply, and that the split-phase centre tap was connected to the bottom point of its 3, and the N of the 2-phase 3-wire 180° was connected to the bottom point of its 3, what would you do to identify which was which?

 

[JohnW2]

Do you believe that those are two different things?

When will you get it that we are not talking about two different things but, rather, two different set of words which people have used/are using to describe one thing?

As I said, there's no more scope for sensible discussion about this, particularly since don't seem to understand what it is that we are discussing.

Kind Regards, John

 

[ban-all-sheds]

This is getting very very silly. Of course it can (and does) exist - since, as we all know, it's a collection of words which the IET is now using to describe something which has been around for decades. Whether the thing which has been around for decades should be refered to by that collection of words is a different matter - but the existence of the thing to which the IET are referring is not in dispute.

Well it's disputed by Tech99.

It was to get you two to look at the actual thing and to ignore the fact that there's been a name change that I wrote:

Forget the 100 years history of split-phase, do you admit the possibility of a 2-phase 3-wire system with a 180° angle?

Tech99 has said that no, there can be no such thing:

Only one phase of current, thus single phase.

 

[ban-all-sheds]

Why do you want to use that c.t. as your common reference point? What's so special about that point?

It's what gives you two simultaneous voltages out of phase with reference to that point.

There will be 2 AC voltages present, and they will not be in phase.

It all depends upon the point you choose as a reference. 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. Use one of the live ends as your common reference point then the voltages as seen at the other end and at the earthed centre point will be in phase (but at different amplitudes).

 

[ban-all-sheds]

When will you get it that we are not talking about two different things but, rather, two different set of words which people have used/are using to describe one thing?

I do get that.

What it took a long time to establish was that Tech99 objected to one set of words not because they were new and different but because they described something which does not and cannot exist.

So not the same objection, if you have one, as you. You said you didn't give a jot, but you have a funny way of showing it.

This whole thing started back on p1/p2 when you were saying things like

And yes, it's all just a matter of terminology. However, the debate that has been re-opened is about the terminology for supplies, not circuits. I (and the BGB) believe that a supply derived from a centre-tapped transformer is 2-phase, whereas Tech99 (and plenty of others in the past) appear to regard it as a single-phase supply.

and Tech99 and ricicle were saying things like

But I see from that other topic that the IEE has now decided this should be called "two phase" even though it isn't. Daft.

It must be single phase as there is only one current.....

At some point you said you'd changed your mind, but I'm now lost as to whether you've changed it back.

As I said, there's no more scope for sensible discussion about this, particularly since don't seem to understand what it is that we are discussing.

The nub of it is whether the IET were right to rename split-phase as 2-phase 3-wire.

But there's also a crucial issue, if you say "they were wrong", of whether you think they were wrong just because they should not have changed it, or because the new name means something which is different from what the old name meant or because the thing described by the new name simply does not exist.

 

[Tech99]

It's what gives you two simultaneous voltages out of phase with reference to that point.

You can get the same by selecting any random point in a circuit in which AC is flowing, including ones which (I presume) you would not try to claim are anything but single phase (e.g. rural house, 2-wire 240V supply from single phase pole xfmr).

 

[ban-all-sheds]

It all depends upon the point you choose as a reference. 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. Use one of the live ends as your common reference point then the voltages as seen at the other end and at the earthed centre point will be in phase (but at different amplitudes).

 

[Tech99]

And?

 

[JohnW2]

At some point you said you'd changed your mind, but I'm now lost as to whether you've changed it back.

I changed my mind only about the currents, when I realised that they were, indeed, 'in phase' in your two speakers (or any other load), and haven't changed my mind back. 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.

I think the disagreements would go away if there were an agreed definition of 'polyphase'. It is being suggested that polyphase requires 'by definition' that out-of-phase currents be present. If that is, or were, correct, than your view, and my inclination to call the situation we're discussing as 2-phase, would, to my mind, fail - but is there such an agreed definition?

Kind Regards, John

 

[Tech99]

It is being suggested that polyphase requires 'by definition' that out-of-phase currents be present.

That's exactly what it is. It's the current which does the work, i.e. causes the lamp to light, produces the magnetic field which causes the motor to turn, etc. So if there aren't at least two currents which aren't in phase with each other, it can't be polyphase.

 

[ban-all-sheds]

So if you have two voltages out of phase with each other, and you connect them to two resistive loads, how do you not end up with the currents out of phase as well?

 

[JohnW2]

It is being suggested that polyphase requires 'by definition' that out-of-phase currents be present.

That's exactly what it is. It's the current which does the work, i.e. causes the lamp to light, produces the magnetic field which causes the motor to turn, etc. So if there aren't at least two currents which aren't in phase with each other, it can't be polyphase.

It's been very clear that this is what you believe but what I don't know is the extent to which it is a 'generally accepted' (well, maybe with a few exceptions ) definition of polyphase. What makes me wonder is that the IET presumably are not working to that definition since, if they were,none of this discussion would have arisen.

Kind Regards, John

 

[ban-all-sheds]

And?

And?

And it is illogical at best and disingenuous at worst to measure the two voltages from the centre tap outwards and declare them to be out of phase and then to insist on measuring the currents from one end towards the tap and on to the other end and say they are in phase.

You cannot have it both ways - assuming no I/V shift, if two voltages are out of phase (and that absolutely involves the concept of direction) then the two currents will be equally out of phase. They have to be.

 

[ban-all-sheds]

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.

 

[Tech99]

You cannot have it both ways - assuming no I/V shift, if two voltages are out of phase (and that absolutely involves the concept of direction) then the two currents will be equally out of phase. They have to be.

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. Draw your secondary winding on the left with two lines across to the right and the load resistances one above the other in series. Call the upper load R1 & the lower R2, the current flowing along your top line I1 and the current flowing along the bottom line I2.

Take the half cycle when the top of the winding is +ve and the bottom -ve. Assuming conventional current flow, the direction of current at that instant will be from the top of the winding (I1), through load R1, through load R2, back to the bottom of the winding (I2), and, of course, through the winding itself back to the top. Now mark which ends of R1 & R2 are the +ve and which are -ve with that flow. You should have the top of both loads as +ve and bottom of both -ve.

So you now have current flow through R1 in a downward direction with the top of R1 +ve and the bottom -ve. You also have current flowing downward in R2 with its top end +ve and its bottom end -ve. Do you agree that the voltage & current relationships are fine so far? Everything is in phase, because there's only one possible current path, right?

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?

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. 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?