How very odd. The "1-phase 3 wire" option is missing from the reproductions of these formes in Appendix 6 of both BS7671:2008 and the 2011 Amendment!
Kind Regards, John
Quick question - Reg number prohibiting SP RCBOs on TT
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Kind Regards, John
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1 phase 3 wire = an engineering impossibility if current flows in all 3 wires under normal circumstances !
That really depends upon what one is taking the phrase to mean, and what you mean by 'normal circumstances'. As I've said before, the arrangement described in 312.1.1 of BGB as 'Single-phase 3-wire (0°)" is what I would call two separate 1-phase, 2-wire supplies with a common neutral. As I said before, the two secondary windings don't even need to be in the same transformer.
Kind Regards, John.
That applies whichever system we're talking about. Although it might not be common practice for power distribution, you could get the 240/480V UK system or the 120/240V American system from two entirely separate transformers; it's only a case of which way round the windings are connected as to whether you get that desired result or something which resembles that odd "1 phase 3 wire" which now seems to be in the wiring regs.
Three phase xfrms for 240/415 in the UK are normally a single unit, but they don't have to be. It's pretty common in the US to find three separate pole mounted xfmrs providing a 3 phase supply.
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Indeed it does - I'm not quite sure why I wrote that (twice!), or what point I was trying to make
Kind Regards, John.
Here's a progression of circuit arrangements which I hope might demonstrate the single-phase nature more clearly, starting with that odd (in power distribution terms) 3-wire arrangement in the new regs.
Here's the system that those new regs apparently now want to call "1 phase 3 wire" with equal voltage secondary windings and two loads R1 & R2 connected:
Again, examine the half cycle when the polarities at the secondary terminals are as shown. Conventional current flow through each load will be as indicated, and I3 = I1 + I2. Agreed?
Now, for our purposes there's no reason why the voltage of the two windings has to be the same. We can change one to suit the load. So let's do that:
The currents are still flowing in the same direction as before, and it's still the case that I3 = I1 + I2. OK so far?
But we don't actually need two separate windings to get our 240 & 480V supplies, the voltages of which relative to the common point at the bottom of the diagram are in phase. We can do it with a single 480V winding and put a centre tap to get the 240V, like this:
For the indicated half cycle, we now have current I3 flowing in the lower half of the winding and I1 in the upper half, whereas with the two separate windings I1 flowed in the upper and I2 in the lower. But currents I1, I2 and I3 as shown have changed in neither magnitude, nor direction. The centre tap of the winding is positive with respect to the bottom end, just as the top of the lower winding in the previous diagram was positive with respect to the bottom end.
So what we now have is effectively the same as before, we've just simplified it by using a single centre-tapped winding to give us two different voltages instead of two separate windings. Nothing else in the circuit has changed, since I1, I2 and I3 are all exactly the same.
But wait a minute... Isn't the supply arrangement in that last diagram now exactly the same as the split phase (the real 1-phase 3-wire) system?
Here's the system that those new regs apparently now want to call "1 phase 3 wire" with equal voltage secondary windings and two loads R1 & R2 connected:
Again, examine the half cycle when the polarities at the secondary terminals are as shown. Conventional current flow through each load will be as indicated, and I3 = I1 + I2. Agreed?
Now, for our purposes there's no reason why the voltage of the two windings has to be the same. We can change one to suit the load. So let's do that:
The currents are still flowing in the same direction as before, and it's still the case that I3 = I1 + I2. OK so far?
But we don't actually need two separate windings to get our 240 & 480V supplies, the voltages of which relative to the common point at the bottom of the diagram are in phase. We can do it with a single 480V winding and put a centre tap to get the 240V, like this:
For the indicated half cycle, we now have current I3 flowing in the lower half of the winding and I1 in the upper half, whereas with the two separate windings I1 flowed in the upper and I2 in the lower. But currents I1, I2 and I3 as shown have changed in neither magnitude, nor direction. The centre tap of the winding is positive with respect to the bottom end, just as the top of the lower winding in the previous diagram was positive with respect to the bottom end.
So what we now have is effectively the same as before, we've just simplified it by using a single centre-tapped winding to give us two different voltages instead of two separate windings. Nothing else in the circuit has changed, since I1, I2 and I3 are all exactly the same.
But wait a minute... Isn't the supply arrangement in that last diagram now exactly the same as the split phase (the real 1-phase 3-wire) system?
If anyone is interested in a few more pages of very similar debate, involving largely the same personalities, from nearly a year ago, you might want to click here .
Kind Regards, John.
Kind Regards, John.
Why?No, why?
Because you seem hell bent on ignoring the 3rd wire. You do drawings without it, and now you say that 2-phase 3-wire must be nonsense because they called it 1-phase before.
Did they call it 1-phase 3-wire before?
TBH I'd never really thought about it, but then there is the generic principle that if you take one thing and split it you could well then have two things.
It wasn't silly, and it was necessary, because another thing you were (and really were, not just seemed to be) hell bent on ignoring was my repeated over and over and over and over again point that you MUST look at it from a particular point of view and that you MUST use the centre point as the point of reference to observe and describe everything from.
And I say that because I started out with the attitude that we have this definition, and I wanted to look at it to see if there's a way which makes it valid, whereas you have started out with the prejudice that it is nonsense and that you will reject anything that shows it not to be nonsense, even if in doing so you engage in willfully ignoring what people say to you over and over again, and even if (as we shall see) you engage in egregious wriggling and moving of goal posts.
It is the introduction of that 3rd point, the centre point, which brings about the change from single-phase 2-wire to 2-phase 3-wire, therefore that 3rd wire must be of fundamental importance.
And there we have it - one of the most outrageous examples of wriggling and goal post moving it has ever been my displeasure to see here.
Shall I count up the number of times YOU used the concept of consistent north to south travel as a way to say that my argument about it being relative to the observer was nonsense?
And as soon as I show you how a model of consistent north to south travel breaks you say I'm being silly? And that you "look at it as the overall picture"? (Said picture having been quite satisfactory to you when you thought that "It's travelling north to south when it's approaching you and it's travelling north to south when it's going away from you. It hasn't changed direction, it's been going in one direction the whole time" was a refutation of my argument.)
If you think for one second that I'm going to let you get away with that you must be mad.
I want you to return to this scenario, and I want you to answer the question.
Our 3 observers:
A says "It changed direction from coming towards me to going away from me".
B says "It changed direction from travelling north to travelling south."
C says "It never changed direction - it just kept going in a straight line".
Please tell me who is right, and who is wrong, and why.
I never asked, and don't want, you to relate it to an electrical circuit.
The question was about something travelling along the edge of a Mobius strip.
You're being asked for your observation of what went on from your perspective. Just as you didn't know, when asked, that you were on a Mobius strip you do not have any way to find out, and never will find out, that you were, so there's no "initially assume", there is just your answer.
From your perspective it had changed direction. A different perspective, a different frame of reference, might yield a different answer, but that doesn't make the answer from your perspective wrong, it's the right answer from your perspective.
There can be no absolute frame of reference which makes all the other ones which differ from it wrong - if that were the case then we could not have separated supplies.
That's exactly what I'm doing.
So I do what you say I can only do, which is to compare the phase of the two voltages by referencing them to some common point, and when I do that and see two different phases (i.e. a non-zero angle between them) I don't have two phases?
When I said "When I do <reference to the common point> I see two voltages out of phase, does that not make it a 2-phase supply?", in what way was your reply of "No. You can only compare the phases by doing <reference to the common point>" not complete rubbish?
We're back to the earlier question - if you (as per that drawing) just considered a load connected across two phases of a 3-phase 4-wire supply, and ignored the other 2 wires, would you have, i.e. as in would you be using to power your load, anything other than a single phase supply?Can you "observe a 2 phase supply" here by using an earth reference at the load end?
But I don't think you'd see that as anything but a single phase supply would you?
As you say, no:
But you also say
The overall picture remains resolutely 3-phase 4-wire. But it's perfectly OK when your frame of reference changes to just two of those wires for you to say it's single phase?
But it's not OK when the frame of reference changes from the two wires of a single phase supply for it to be said that it's 2-phase 3-wire?
And it's OK to insist that no perspective of change in direction of travel only in relation to the observer can be right because the overall picture is one of unchanging south to north except when, oh dear, the observer is at the North Pole at which time the overall picture suddenly becomes just a straight line and the previous overall picture is silly?
And the latter still hasn't caused the penny to drop?
Jolly good.
I was, earlier, happy to leave a number of amusing rhetorical questions which I thought would cause the penny to drop for you, but alas that didn't work, so now we'll see if actually answering them will make a difference.
So, what about circumpolar travel?
Would your direction change as you crossed the North Pole and went from travelling north to travelling south?
What about the train? Which direction would the train be going as it crossed the pole? North or South?
The trains and cars travelling along "dead straight" tracks and roads across the poles, or trains going from Euston to Kings Cross via Rugby etc are not meant to be analogies of electrical circuits.
They are meant to be ways to get you to see that where an observer is, and what his frame of reference is, are going to affect what he observes, and that what he observes is reality for him. That's why so many were rhetorical with a whimsical "How can that be, I wonder?".
The fact that a different observer with a different frame of reference will observe something different does not make either one wrong. But I am truly beginning to think that you really do not get that.
Here's another one for you.
You are driving from Birmingham to Oxford.
I am driving from London to Oxford.
Are we travelling in the same direction, or different directions?
Which, and why?
There is a reality when you only refer to 2 out of the 4 wires of a 3-phase 4-wire supply which is single-phase 2-wire.
There is a reality when you only refer to 2 out of the 3 wires of a 2-phase 3-wire supply which is single-phase 2-wire.
And there is a reality when you refer to 3 out of the 3 wires of a 2-phase 3-wire supply which is 2-phase 3-wire.
On p 338 of BS 7671:2008 it lists 2-phase 3-wire.
On p 294 of BS 7671:2001 Amd 1 & 2 it lists 2-phase 3-wire.
It's been a supply type in BS 7671 for at least 11 years. It's not new.
The arrangement at the generation end of the transmission can be totally different to the arrangement at the load end.
Can you not accept that ?
A phase ( a voltage ) of a supply has to have 2 terminals no more, no less.
If there are two supplies ( two voltages ) each must have two teminals. It is possible for two terminals, one and only one per phase, to be connected together to share one wire in the transmission system.
The two supplies sharing one wire ( of three wires ) can be different in voltage and frequency. If they are the same frequency the phase angle between them can be anything from 0 to 359.99999999 degrees.
The various connection methods ( star and delta being the most common ) all obey that rule.
Can you not accept that ?
A phase ( a voltage ) of a supply has to have 2 terminals no more, no less.
If there are two supplies ( two voltages ) each must have two teminals. It is possible for two terminals, one and only one per phase, to be connected together to share one wire in the transmission system.
The two supplies sharing one wire ( of three wires ) can be different in voltage and frequency. If they are the same frequency the phase angle between them can be anything from 0 to 359.99999999 degrees.
The various connection methods ( star and delta being the most common ) all obey that rule.
Indeed - but we acknowledged last night that this was true in terms of the forms in the Appendices of BS7671, and that it goes back further than you suggest - at least as far as 1992. However, the point is that it appears that BS7671:2008 Amd 1 (2011) is the first version which has actually explained what they mean by 2-phase 3-wire (and the same w.r.t. '1-phase 3 wire (0°)')
AS above, in trems of their forms (PIR, IEC etc.) both 2-phase 3wire and 1-phase 3-wire have existed for at least 20 years, but neither of those descriptors appears to have been defined/described until 2011.
Kind Regards, John.
Well - unless someone is going to try and claim that until recently the IET meant something different (which would require them to tell us what the IEE/IET did mean by "2-phase 3-wire" between 1992 (or earlier) and 2011) that should put an end to all the complaining about a recent change which is wrong.
Either that or they will have to adopt the position of "The IEE/IET have been wrong for at least 20 years and nobody has noticed except me, because I know so much more than all the people who have sat on JPEL/64 for all that time".
Either that or they will have to adopt the position of "The IEE/IET have been wrong for at least 20 years and nobody has noticed except me, because I know so much more than all the people who have sat on JPEL/64 for all that time".
I'm inclined to agree - which is why, a day or two back, I started questionning whether there really has been any change in the views/terminology of the IET, even if others have been assuming some other 'long-established' terminology.
Kind Regards, John
It would have been helpful if you'd done that a week or two back, not a day or two...
But then I wouldn't have had the opportunity to help Tech99 think about the fact that everything is relative.
But then I wouldn't have had the opportunity to help Tech99 think about the fact that everything is relative.
Of course it would - and helpful to me as well as eveyone else! However, since people were so strongly asserting that there had been a change (and then critising that alleged change), it (naively) didn't occur to me (or you!) to question whether a change had really happened!It would have been helpful if you'd done that a week or two back, not a day or two...
All that is clear is that, even though the IET had been using the same terminology (at least, in their forms) for a long time, it seemingly wasn't until 2011 that BS7671 made an attempt to define what they were using these terms to mean.
Kind Regards, John.
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