Single phase, 2 phase, 3 phase etc

ericmark said:

With a split phase the two supplies are in phase with each other so it is still single phase.

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180° out-of-phase, surely? If they were in-phase, there would be no p.d. between them - they would effectively just be two single-phase supplies in parallel.

ericmark said:

I am not saying it does not exist but 2 phase supplies must be quite rare. In Europe since we don't use the two supplies of a split phase without the neutral it would not really matter if the supply was 2 phase or split phase.

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I do not understand the distinction you are making. What is your understanding of "2-phase"?

ericmark said:

I suppose with USA being 120 volt then 2 phases would be 207 volt ....

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That assumes 120° between phases, so would only be true if the "2 phases" were actually two of the phases of a 3-phase system. As above, I would expect a true 2-phase system to have 180° between phases (i.e. 'split phase'), hence 240V between phases. Again as above, if the two were in-phase, then the p.d./voltage between them would be zero.

Kind Regards, John

ericmark said:

Table 7A phase 2 of AC = black so for 110 volt brown, black, green/yellow

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Does that table not specify black only for phase 2 of a 3-phase supply though? With 110V CTE we don't have a 3-phase supply, only single phase, and the only color it lists for the live of a single-phase a.c. supply is brown. So while it might well be sensible within a larger distribution system to use two different colors to identify each live leg of the supply (and is certainly what I would do), I don't think that strictly speaking it would be compliant with the new scheme unless you sleeved brown at the terminations.

Either way, when it comes to the flex on U.K. 110V tools, although normally brown & blue everybody knows that each conductor will be at 55V (or 63V) to earth anyway, so there's really no room for confusion.

We tend to call them phase colours, but clearly also used with split phase

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Indeed, and it would certainly make sense to identify the two outers of such a system throughout an installation. It's just that under the new scheme I don't believe that the strict letter of the regulations permits that (although in practice sleeving brown at terminations would comply and still allow easy identification throughout).

I am not saying it does not exist but 2 phase supplies must be quite rare.

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Certainly they must be these days. I know that in a few U.S. cities there were still some 2-phase 4-wire supplies until quite recently (1990's perhaps?) which were maintained for things such as old elevator motors. There might still be a few left now, but no doubt they'll disappear entirely as old plant is finally replaced with new 3-phase gear.

I suppose with USA being 120 volt then 2 phases would be 207 volt so maybe a 220 volt AC would work, but using a 240 volt AC would have the same problem as in Algeria.

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It's usually listed as 120/208V here, and certainly 230-240V motors can have a problem, allowing for the normal variation in supply voltage from nominal. Sometimes a buck-boost transformer is employed to run 208V equipment on 240V or vice versa.

Many straightforward resistance heating units are dual-rated for 208 or 240V use however, obviously with a lower rated output on the lower voltage. There are other heaters which are dual-rated for 240 or 277V, the latter being another standard utilization voltage here.

JohnW2 said:

180° out-of-phase, surely? If they were in-phase, there would be no p.d. between them - they would effectively just be two single-phase supplies in parallel.

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The voltages at each outer with respect to the neutral are 180 degrees out of phase with each other, but the current through the winding as a whole must always be in the same direction and at the same instantaneous value at any given instant.

What is your understanding of "2-phase"? That assumes 120° between phases, so would only be true if the "2 phases" were actually two of the phases of a 3-phase system.

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The original 2-phase, such as that used for the old elevator motors I mentioned above, was delivered over two separate pairs of wires with the currents 90 degrees out of phase with each other.

As you say, if we take only two phases from a 3-phase wye supply then the voltages must be 120 degrees different from each other with respect to the neutral. This can be found in some apartment buildings here. While a regular single-family home is almost always supplied with a 120/240V single-phase 3-wire supply, apartment blocks may have a 120/208V 3-phase 4-wire wye supply, with each apartment being fed with only two of the three available phases. They use the same distribution panels as a regular home (neutral plus a double-pole main with two live busbars), but the live-to-live voltage will be only 208V instead of 240V.

PBC_1966 said:

The voltages at each outer with respect to the neutral are 180 degrees out of phase with each other ...

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Would they not be 180° out-of-phase with respect to anything? The consumer might not even use the neutral, in which case they would simply see the L-L pd, which would be double the L-N pd, and then would no nothing about L-N voltage or phase.

PBC_1966 said:

... but the current through the winding as a whole must always be in the same direction and at the same instantaneous value at any given instant.

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Sure (assuming the supply derives from a centre-tapped winding, or equivalent) - but the consumer sees/knows nothing about that.

PBC_1966 said:

The original 2-phase, such as that used for the old elevator motors I mentioned above, was delivered over two separate pairs of wires with the currents 90 degrees out of phase with each other.

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That's a little different from the (3-wire) 2-phase 90° supply described in BS7671 - which recognises three variants of 2-phase - 90°, 120° and 180° (all of which are 3-wire).

Kind Regards, John

JohnW2 said:

Would they not be 180° out-of-phase with respect to anything?

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What else is there to compare them against except the center-tap neutral?

consumer might not even use the neutral, in which case they would simply see the L-L pd, which would be double the L-N pd, and then would no nothing about L-N voltage or phase.

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As with 110V CTE U.K. site transformers. It's just a single-phase 110V secondary which happens to have an earth connected to the middle of the winding.

That's a little different from the (3-wire) 2-phase 90° supply described in BS7671 - which recognises three variants of 2-phase - 90°, 120° and 180° (all of which are 3-wire).

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Not sure exactly what configuration the 3-wire 90-degree one is there, but of course if you start with two windings and 4 wires you could combine into 3 wires by commoning one side of each. Is that what's described?

As for the 3-wire 180-degree business, I remember the IET coming out with the announcment that henceforth BS7671 was going to classify the 3-wire single-phase (or "split phase") arrangement as being 2-phase from now on. Totally illogical, and goes against over a century of it being recognized as single phase, not to mention that the rest of the world is still going to regard it as single phase.

PBC_1966 said:

As for the 3-wire 180-degree business, I remember the IET coming out with the announcment that henceforth BS7671 was going to classify the 3-wire single-phase (or "split phase") arrangement as being 2-phase from now on. Totally illogical, and goes against over a century of it being recognized as single phase, not to mention that the rest of the world is still going to regard it as single phase.

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As I've just been reminded 'off-line', we've done this discussion to death in the past. Whilst I agree that it's meddlesome and potentially confusing to change terminology that has existed for "over a century", I still struggle a little to understand that long-established terminology. So, at risk of repeating that "doing to death" .....

For someone provided with a 2-wire supply, the issue is obviously moot. The only option they have is to connect loads between the two incoming conductors, and all they 'see' or know is the pd between those two conductors - the issue of 'phase' is therefore essentially meaningless. However, things change as soon as they are also provided with a 'neutral', with the option to connect loads L-N and well as L-L. It then seems perfectly reasonable to talk about the phases of the two L's relative to that neutral, and since (unless it's a silly supply, with parallel conductors!) the two Ls won't have the same phase (relative to neutral), it seems perfectly reasonable (to me) to call that '2-phase'.

What I've just said does not really depend upon what the magnitude of the phase difference is, so I wonder what you feel about the terminology for someone supplied with two phases (and N) from a three phase source (i.e. the two Ls 120° apart, relative to N). Do you again regard that as "single phase"? I suspect not.

Your argument seems to be based on considerations of how the supply is derived, but what if you think of the source as just being 'a black box'? The impression I get (maybe incorrectly) is that you would accept a 3-wire system as "2-phase", if the phase difference were 90° or 120°. If that's true, you might even accept it as "2-phase" if the phase difference were 150°, or even 170°. If that's all true, then what's so special about 180° which means that it is not "2-phase"?

Kind Regards, John

PBC_1966 said:

As for the 3-wire 180-degree business, I remember the IET coming out with the announcment that henceforth BS7671 was going to classify the 3-wire single-phase (or "split phase") arrangement as being 2-phase from now on. Totally illogical, and goes against over a century of it being recognized as single phase, not to mention that the rest of the world is still going to regard it as single phase.

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I have been a member now for around 10 years I do not recall that. Maybe you can clarify?

ericmark said:

I have been a member now for around 10 years I do not recall that. Maybe you can clarify?

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Amendment 1 of BS7671:2008 (2011, green book) was the first to include diagrams of various supply setups in Chapter 31, where it describes a 3-wire centre-tapped winding set-up as "180 2-phase" (not "split phase"). Without a lot of searching, I don't know what (if anything) it previously described such supplies as.

Kind Regards, John

JohnW2 said:

I don't know what (if anything) it previously described such supplies as.

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3-wire single-phase. Have a look in the scanned section A of the 14th edition from the other current thread, and you'll see references to it, e.g. A.2.

PBC_1966 said:

3-wire single-phase. Have a look in the scanned section A of the 14th edition from the other current thread, and you'll see references to it, e.g. A.2.

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Fair enough. It's even possible that that persisted right up to the original version of the 17th ed. (2008), since, as I said, in the absence of the section about types of supplies that first appeared in the 2011 Amendment, I wouldn't really know where to look for it! The index doesn't help, and the only vaguely relevant text in the corresponding chapter refers only to "single-phase two-wire" and "three-phase four-wire".

Kind Regards, John

JohnW2 said:

in the absence of the section about types of supplies that first appeared in the 2011 Amendment, I wouldn't really know where to look for it!

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I would think there must still be some reference to it in the original 17th edition, possibly in sections about isolation of live poles or similar. Also, take a look at the model electrical installation certificate; you'll find it listed along with 2-wire single-phase and 4-wire 3-phase under the supply types.

Here you go - The forms from 2008, go to page 6 of the PDF:

http://electrical.theiet.org/wiring-regulations/forms/2008.cfm?type=pdf

Earlier & later versions also available:

http://electrical.theiet.org/wiring-regulations/forms

PBC_1966 said:

I would think there must still be some reference to it in the original 17th edition, possibly in sections about isolation of live poles or similar. Also, take a look at the model electrical installation certificate; you'll find it listed along with 2-wire single-phase and 4-wire 3-phase under the supply types.

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PBC_1966 said:

Here you go - The forms from 2008, go to page 6 of the PDF: http://electrical.theiet.org/wiring-regulations/forms/2008.cfm?type=pdf.

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So it does, and if you look at the corresponding form in Amendement 1 (2011), you will see that the "1-phase, 3-wire" option has disappeared. We therefore seem to have pinpointed the point in time at which the IET changed it's terminology.

Kind Regards, John

I knew it was only very recently, as I remember seeing the announcement about it and discussing it elsewhere. Why they suddenly decided upon this confusing change out of the blue, I have no idea.

PBC_1966 said:

I knew it was only very recently, as I remember seeing the announcement about it and discussing it elsewhere. Why they suddenly decided upon this confusing change out of the blue, I have no idea.

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As I wrote yesterday, I agree it's meddlesome and potentially confusing when someone, or some body, unilaterally changes some very-long standing terminology (like "light bulb") .

However, as I said, I nevertheless personally found that original terminology confusing and illogical, but you have not yet responded to that comment. I've always thought of these things from the POV of an installation/user, which/who receives a 3-wire supply from a 'black box', the inner workings of which I know nothing about. On that basis, I find it just as illogical to call it "single phase" when two of the wires carry voltages which are 180° out-of-phase (wrt. the third wire) than I would to call it "single phase" if the phase difference was 90° or 120°.

... unless, of course, you call 90° and 120° 3-wire systems "single phase", in which case you would at least be being consistent - but I suspect that is not the case!

Kind Regards, John