Single phase, 2 phase, 3 phase etc

Mattatooi said:

All control (mixing desks, radio racks, 1ph amp racks (for monitors), backline (instruments, amps) etc are ALL on the same phase (all the single phase outlets are on the same phase on the distros) and generally all the larger amps for PA are then wired evenly across all 3 phases. (most of the distros have a ton of 13/16/32a 1ph and then 4 or so 32a3ph and usually 63a1ph x 3 on each phase and also usually a 63a3ph through) So as a result you end up with a little more load on the first phase. The reason being, which I have been told, is that if there was a fault between an instrument and the sound equipment on different phases you would then have a potential difference 208v.

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One of the standard 3-phase systems here in the U.S. is 120/208V, but as you appear to be in Northern Ireland, you'd have 230/400V, i.e. the voltage from any phase to neutral/earth is 230V but the voltage between any two phases is 400V.

But you'd have to have a pretty unlucky set of multiple faults in order to end up with 230V mains on two separate pieces of equipment such that you get 400V between them. And even though it could happen (however unlikely), it could just as easily happen between your low-power preamps, mixing desk etc. and one of the power amplifiers.

That's not to say that this unlikely sort of set of circumstances has never been considered.....

If you have a 3phase supply, what prevents potential differences? Perhaps modern day MCBs etc prevent this, and its become just habit for some of the longer lasting companies around.

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No, if you have a standard 3-phase supply, you'll have 400V between phases. That's just the way the system works: The phase-to-phase voltage will be equal to the phase-to-neutral voltage multiplied by the square root of 3.

There used to be rules in the IEE Wiring Regs. which attempted to minimize the chances of this higher voltage appearing between two pieces of portable equipment in close proximity even in the event of the unlikely combination of faults all occurring at the same time. They specified that sockets within one room of domestic premises must never be on different phases, and that even in commercial environments there could be more than one phase on sockets within the same room only if it was impractical not to do so and then only if sockets within each area of the room were grouped together by phase and at no point were two sockets on different phases within 6 ft. of each other.

The same rules applied to the single-phase 3-wire supplies we're discussing here (and to the old 3-wire d.c.supplies), in which the voltage between sockets on different phases was generally even higher than that between phases on a 3-phase system (up to 500V in some cases).

PBC_1966 said:

JohnW2 said:

Sure, but that's at least partially because 120° is not half of 360°, whereas 180° is. I wonder what would happen with a hypothetical "4-phase" supply?

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Hmmm.... That's an interesting one because if you were talking about evenly spaced currents around a phase vector diagram (i.e. 90 degrees between), I think that effectively you'd end up with a 2-phase system.

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I'm not totally sure of what you mean by that, since you would obviously have four different phases present (as you would see if you connected each to an input of a 'scope, with neutral connected to the common input). The reason I mentioned it was because one would then have two pairs of 'phases' which were 180° out-of-phase with one another. In the context of a 3-wire system, you appear to feel that there is something special/'magic' about 180° - in that it represents "single-phase", whereas, say, a hypothetical 170° would represent "2-phase". Your comment that a 4-phase system might "end up as a 2-phase system" might suggest that you are again regarding 180° as 'magic'!

PBC_1966 said:

I'd be interested to hear of your 'suspicions', which I guess are probably 'political' in some sense!

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Upon reflection, I wonder if it was done in an attempt somehow to try and "simplify" things for those with a good knowledge of what BS7671 says but without a real grasp of fundamental electrical principles.

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Possibly - although, as you realise, I think there is perhaps a more logical reason than that (which I suppose would again be 'simplification'). The oscilloscope scenario mentioned above would appear to be the most obvious way of indicating how many 'phases' one had been supplied with - and that would show two out-of-phase waveforms with the 3-wire system we are discussing - just as it would show one waveform with single-phase and N out-of-phase waveforms with any other "N-phase" supply.

PBC_1966 said:

In the case of an installation which takes a 3-wire 240/480V service or 2 phases from a 240/415V 3-phase network, the basic requirements with regard to switching, fusing etc. are similar - Single-pole switching must be in the live poles only, fuses must be in the live poles/phases and not in the neutral, etc.

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That's true, but it's surely equally true with single-phase loads in a single-phase or 'full' 3-phase installation?

PBC_1966 said:

Maybe I'm way off the mark, but it's just a suggestion.

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Your suggestion/guess is as good as anyone else's. I take it that there has never been any official 'explanation'? I can but repeat what I said before that, since they were proposing a change to something which was very long-established, they surely must have believed that there was a fairly compelling reason for the change.

Kind Regards, John

PBC_1966 said:

There used to be rules in the IEE Wiring Regs. which attempted to minimize the chances of this higher voltage appearing between two pieces of portable equipment in close proximity even in the event of the unlikely combination of faults all occurring at the same time. They specified that sockets within one room of domestic premises must never be on different phases ....

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Indeed, but I always felt that was based on 'emotion' ('misguided intuition') more than anything else. In the very unlikely event of the combinations of faults required, a pd of 230/240V is more than enough to injure/kill, and I'm far from convinced that the risk (to life/limb) would be materially higher if the pd were 400/415V.

... a bit like the "415V pd labels". I never really understood what precautions one was expected to take if pds of 415V were present that one would not (be advised to!) take if the pds were "only" 240V!

Kind Regards, John

I sometimes wonder what's really behind all of the doors one sees which say "Danger: High Voltage".

JohnW2 said:

In the context of a 3-wire system, you appear to feel that there is something special/'magic' about 180° - in that it represents "single-phase", whereas, say, a hypothetical 170° would represent "2-phase". Your comment that a 4-phase system might "end up as a 2-phase system" might suggest that you are again regarding 180° as 'magic'!

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It's "special" in the sense that by simply swapping the connections to some component you can obtain a 180-degree phase shift of the current in that component relative to some other component, e.g. your LED examples.

In the hypothetical 4-phase supply, since two of the phases are effectively just "mirror images" of the other two, you could achieve nothing that could not also be achieved by using a 2-phase supply and a suitable arrangement of connections. For example, suppose you had a 4-pole motor. You could wire one field coil to each phase with a common point to the neutral and generate a rotating magnetic field. But why would you want to go to all that trouble? You could achieve exactly the same result with a 2-phase (90-degree) supply and opposite poles of the motor connected to the same phase but with the connections to one coil of each pair reversed (which is exactly what was done with some of those early motors designed to run on 2-phase supplies).

Possibly - although, as you realise, I think there is perhaps a more logical reason than that (which I suppose would again be 'simplification'). The oscilloscope scenario mentioned above would appear to be the most obvious way of indicating how many 'phases' one had been supplied with - and that would show two out-of-phase waveforms with the 3-wire system we are discussing - just as it would show one waveform with single-phase and N out-of-phase waveforms with any other "N-phase" supply.

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But as I said earlier, the fact that you can hook up an oscilloscope to various points of a system and see two voltage waveforms which are 180 deg. out of phase doesn't "prove" that you have 2-phase supply, since as I think you've already acknowledged, you could obtain a similar display by making suitable connections within an arrangement which you would accept as being single phase.

And if you want to consider the number of out-of-phase waveforms one can obtain on a 'scope display as being indicative of the number of phases of the supply, what would happen if you tried it on a 3-wire 3-phase delta supply?

That's true, but it's surely equally true with single-phase loads in a single-phase or 'full' 3-phase installation?

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Of course. I was just wondering whether the idea was to stop somebody thinking "1-phase system, so just switches & fuses in one line."

Your suggestion/guess is as good as anyone else's. I take it that there has never been any official 'explanation'?

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Not that I've ever seen. I don't in any way agree with the decision, but it would be interesting to see some sort of explanation as to why they made it.

I suppose also it could be some Euro-Norm/CENELEC thing which they're mirroring, since everything in the U.K. wiring regs. now has to conform with harmonized European systemsas far as possible it seems. But if so, then naturally that would just lead us to wonder why the relevant European committee made the change.

PBC_1966 said:

It's "special" in the sense that by simply swapping the connections to some component you can obtain a 180-degree phase shift of the current in that component relative to some other component, e.g. your LED examples.

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Well, yes, it's 'special' in the sense that it's the only phase change that one can achieve simply just by manipulating connections - but in terms of physics and maths, 180° is no more special than 90°, 120° or even 170° or 179°.

PBC_1966 said:

In the hypothetical 4-phase supply, since two of the phases are effectively just "mirror images" of the other two, you could achieve nothing that could not also be achieved by using a 2-phase supply and a suitable arrangement of connections.

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True - but, to my mind, the fact that one could achieve the same (by reversing some of the connections) with a 2-phase supply doesn't alter the fact that what one has been provided with is a 4-phase supply.

Are you saying that (because of the above) a 4-phase supply should be called "2-phase" and that a 6-phase supply should be called "3-phase"?

PBC_1966 said:

But as I said earlier, the fact that you can hook up an oscilloscope to various points of a system and see two voltage waveforms which are 180 deg. out of phase doesn't "prove" that you have 2-phase supply, since as I think you've already acknowledged, you could obtain a similar display by making suitable connections within an arrangement which you would accept as being single phase.

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Yes - but, as above, I do not feel that what one can achieve by manipulating connections alters the nature of the supply with which one has been provided.

PBC_1966 said:

And if you want to consider the number of out-of-phase waveforms one can obtain on a 'scope display as being indicative of the number of phases of the supply, what would happen if you tried it on a 3-wire 3-phase delta supply?

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That would require an unusual sort of 'scope' with three pairs of independent, isolated, inputs - but, if one had such a machine, one would presumably see the three expected out-of-phase waveforms.

PBC_1966 said:

I suppose also it could be some Euro-Norm/CENELEC thing which they're mirroring, since everything in the U.K. wiring regs. now has to conform with harmonized European systemsas far as possible it seems. But if so, then naturally that would just lead us to wonder why the relevant European committee made the change.

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That's very possible - and maybe the Europeans didn't make a recent change but, rather, we have been 'forced' to align ourselves with terminology they have been using for a very long time? If he's around, stillp may be able to help us on this one!

Kind Regards, John

JohnW2 said:

If he's around, stillp may be able to help us on this one!

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He is, what was the question?

stillp said:

JohnW2 said:

If he's around, stillp may be able to help us on this one!

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He is, what was the question?

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Do you have any insight into what resulted in the change (first seen in Amendment 1 of BS7671:2008) from what was apparently the "established for 100 years terminology" of "split-phase" ('3-wire single-phase') to "180° 2-phase". Specifically, was the change perhaps 'Europe-driven', or what?

Kind Regards, John

I'm not certain, but I think it was introduced into the IEC60364 series by the USA. This was then harmonised in Cenelec.

stillp said:

I'm not certain, but I think it was introduced into the IEC60364 series by the USA. This was then harmonised in Cenelec.

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Thanks. That was was rather suspected. If you had time to plough through this thread (and similar ones in the past - particularly around 2011), you'll see that I appear to be one of the few people who thinks that this (seemingly) 'harmonised new terminology' is actually more logical than that which preceded it- although I do agree that to change something that has been accepted for decades is a source of potential confusion!

Kind Regards, John

stillp said:

I'm not certain, but I think it was introduced into the IEC60364 series by the USA. This was then harmonised in Cenelec.

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Seems rather unlikely given that on this side of the pond the IEC is regarded very much as a Europe-dominated organization and American standards are firmly entrenched in ANSI, NEMA, etc. And the normal residential supply here is still most definitely labeled as 3-wire single-phase everywhere you look, be it the distribution panel, the local utility company's tariffs, the NEC, etc.

PBC_1966 said:

stillp said:

I'm not certain, but I think it was introduced into the IEC60364 series by the USA. This was then harmonised in Cenelec.

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Seems rather unlikely given that on this side of the pond the IEC is regarded very much as a Europe-dominated organization and American standards are firmly entrenched in ANSI, NEMA, etc. And the normal residential supply here is still most definitely labeled as 3-wire single-phase everywhere you look, be it the distribution panel, the local utility company's tariffs, the NEC, etc.

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ANSI is the US member organisation of the IEC. One of the problems with acceptance (or lack of) of international standards in the US is the number of organisations that develop standards; NEMA, NFPA, and SEMI being just a few examples. It is actually quite common at the Working Group level in IEC for the US members to disagree with standards published by these organisations.

Maybe that's part of the problem of why so many of these international committees are often not well regarded in the U.S., since those involved most closely with them are more "in tune" with the European-slant that they have.

I know that certainly some years ago there were often considerable points of contention here with decisions made by the ITU. On more than one occasion there were cases of the ITU adopting some telecommunications signaling or other protocol which was heavily based on current European practice and which often paid little more than lip-service, if that, to established North American practices. Then there would be grumblings from some levels of the ITU when the U.S. didn't fully adopt the "established international protocol," completely ignoring the fact that the U.S. requirements had been all but ignored in the decision-making process.

I can't speak for the ITU, but certainly in IEC and ISO, the US requirements are never ignored by the other members. However those US requirements are often overlooked by the private US organisations that make money out of standards.

I remember, in the 80's/90's responding to RFPs from Govt/public sector customers who had had a requirement to use, or at least mandate support for, the ISO OSI protocols imposed on them, when all they wanted to do was implement TCP/IP and get on with life.

We always responded in the same way - yes of course we support OSI, and tick the boxes in the mandatories, but advised on the realities of lack of developed standards and widespread adoption and real-world interoperability etc, and suggested that as an interim solution the customer make a strategic decision to temporarily use TCP/IP.

Apart from people wanting X.25 for leased lines and ISDN, nobody ever bought the OSI stuff, and never regarded the official "thou shalt" as anything other than a pointless imposition to be swerved around as quickly as possible.