Talk:Three-phase electric power

While this article talks about star arrangements for electrical machinery, it does not discuss Delta arrangements, which do not require a neutal connection, because there isn't one available. Also, the function of Earthing is not discussed. - kiwiinapanic 11:28 Feb 9, 2003 (UTC)

You do not need a neutral connection to run in a Star configuration (e.g. in a motor), all current in one phase will return via the two other. If in a 400V TN-configuration you will need the neutral to extact 230V between one phase and neutral for normal appliances. KjellG visitor from no.wiki.

I believe Europe now uses 230 VAC supply (the average of UK's 240 VAC and continent's 220 VAC). - anon 24-May-2003

sort of the official standard is now 230V BUT it has such a wide tollerance band that both 220 and 240 are well within spec

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This page is still riddled with errors. UninvitedCompany 12:32, 6 Oct 2003 (UTC)

Rotating field illustration

The rotating motor looks fine, but what does it illustrate? Beeing an engineer in electronics with some credits in electric machinery: this is different from anything I have ever seen. Can anyone explain this illustration? KjellG visitor from no.wiki

Agreed. This diagram seems to illustrate the summation of the three phases, each represented as vectors, as their magnitude changes. While this ultimately results in a point which moves on a circular locus, it is neither indicative of what is happening electrically within the motor, nor does it give a useful way of understanding how the magnetic field rotates. Trouble is, as an electrical engineer myself (like KjellG), I can't say I have a better solution for a graphical representation. MDM visitor.

Question: Does the illustration indicate CW or CCW rotation, and based on which end of the motor? I sold motors for years and years, (G.E.) and it was my understanding that three phase motors are factory wound for CW rotation looking at the shaft end of the motor, and wired L1 L2 L3. To reverse exchange any two leads. Scott P - Washington —Preceding unsigned comment added by 67.185.55.200 (talk) 02:20, 3 March 2010 (UTC)

"two-phase" power in U.S./Canada is not quite right

"Two-phase" power in U.S./Canada is not quite right. Electrical grounding/earthing is "center tap", meaning that each small group of homes has a 240V transformer, with ground/earth tied to the middle. This makes the two opposite 120V sides exactly 180° apart, making them in-phase, and therefore considered single phase by most electrical engineers. Many appliances, including the central (forced-air) heating unit in my apartment, can operate anywhere from 208V to 240V, but the BTU/kW power and heating capacity ratings change correspondingly. Only resistive loads ignore phase like this though, whereas inductive loads like AC motors must have the phase[s] they were designed for. Larger commercial buildings almost always have three-phase, and sometimes do use true 208V two-phase for certain things, such as ballast for fluorescent lights. –radiojon 05:41, 2004 Feb 16 (UTC)

Connecting a ballast between A and C of a three-phase system does not make it a "two phase" load, it's a single-phase load connected line-to-line. And just to further confuse the issue, you can run a three-phase motor on single-phase power, though it will need help to get started and you usually don't plan to do this delibrately. --Wtshymanski 23:10, 16 Dec 2004 (UTC)

ERROR! You can run an asyncronus (Or syncronus motor) on singlephase, After it is started!and if it is provided with a single-phase winding. BUT if yoou try to connect a three-phase motor to single phase you will usually blow a fuse since the current will bi wery high. Disconnecting one pnase will in practice mean that you try to run a three-phase motor on one phase and results in far to high current and will burn the motor, that is teh reason for the normal special three-phase breaker with thermoelements that will disconnect all three phases if one is lost (And also if the motor is braked to much).

Small refrigerators and fan motors can be run on one-phase motors if equipped with a starting phase, usually generated with a electreic condensor in series with the second phase winding, usually connected with a high current relay when starting and disconnected when motor is started and current is dropping. Electric syncronous clocks use a permanent second phase obtained with a shortcircuit winding on part of the stator pole, they are somewat inefficient put cheep and durable.Seniorsag (talk) 13:58, 30 January 2012 (UTC)

You're right. While there was at one time a fair amount of two-phase power in the U.S. (four wire service; two pairs 90 degrees out of phase), this hasn't been the case for decades. The two-phase systems had the advantage that the windings are the same for a capacitor-start single phase motor and a two-phase motor; that is, they are 90 degrees apart. Three phase service can be derived from two phase and vice versa using transformers.

The article is a mess right now because, as with the other electrical topics, there is so much difference in practices around the world that it is hard to make an integrated article, particularly since there aren't any contributors who have more than passing familiarity with practices outside their own country. UninvitedCompany 20:00, 17 Feb 2004 (UTC)

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Three phase systems have a very nice property, that if they are loaded by a linear load, the amount of power transferred is constant, it does not have a 50 or 60Hz ripple. This means that three-phase motors and generators do not have the vibrations associated with one or two phase motors.

I believe this is the reason for the popularity of the three phase system, as it allows enormous amounts of power to be generated using relatively light machines. If there were a ripple in the power, the machines would need to be very heavy to not be blown to bits by the it.

Would this be interesting information to put on this page?

Evert van de Waal

This is now worked out in some detail in the three phase article. --Wtshymanski 04:16, 31 Dec 2004 (UTC)

And, as as layman, someone explained 3-phase to me and commented that different houses in a street (or streets in a town) would be on different phases, whilst at the generating station 3-phase generation was most efficient. I found that very significant way to appreciating how I'd never known about it before - yet it was a ubiquitous feature. Would someone with a good understanding like to insert a short explanation of that feature. 134.244.154.182

Practices vary, and I'm speaking from a North American viewpoint, but often a branch feeder from a substation will be three phases but individual homes are only single-phase loads. I suppose you could dedicate a street per phase, but I'd expect to see that only in rural areas - in more densely populated places I've seen a three-phase feeder down the street and houses connected A,B,C...on either side. --Wtshymanski 23:10, 16 Dec 2004 (UTC)

High Leg

The voltage difference between the phases and neutral is different in the US, the article mentions a "high leg". Can someone who understands the subject explain this a little further? I know that in Europe the voltage between all three phases and neutral is the same. Is there also a "high leg" in countries other than the US? 24.77.134.211 (talk) 02:50, 25 February 2008 (UTC)

phase sequence

from one of the images on your page Triplex outlet. The top 3 are used to run a phase sequence indicator comprised of 3 neon night lights. The bottom three run the desired triplex load. May i ask how exactly can neon lights indicate phase seqence? Plugwash 21:44, 26 Sep 2004 (UTC)

Beats me. You can interconnect lamps, capacitors and inductors to build a phase secquence indicator but that's not what the photo shows. I've never heard of or seen anyone attempt to supply a three-phase load with three regular duplex plugs - three-phase gear always has ONE plug with all phases in it. The photo is misleading because it shows a practice that is at the very best dubious and is almost certainly against any electrical code!

The most important thing about three-phase power is not the colo(u)r of the wires - this needs reorganization. All the stuff about testing is a bit too much "how-to manual", I think, for an encyclopedia...the article on heart I'm sure doesn't tell you how to start cutting for a transplant.

An article on the differences between UK and North American terms for electrical terms might make a good short Wiki project.

And on another matter: Anyone feeling up to explaining phasors and symmetrical components? Or higher phase order systems? --Wtshymanski 23:10, 16 Dec 2004 (UTC)

The more I look at the "triplexing" part of the article, the less I like it. I've never heard of such a scheme being used (three separate receptacles being used to power a single three-phase load - too error-prone to ever exist outside, perhaps, a laboratory situation). I'd like to remove that illustration as soon as I can get some proper images of real three-phase outlets. --Wtshymanski 04:16, 31 Dec 2004 (UTC)

there's a couple of images over at Industrial & multiphase power plugs & sockets e.g. the one to the right of this comment. or I intend to upload a 3P+N+E image soon.--Ali@gwc.org.uk 08:27, 31 Dec 2004 (UTC)

I can see how such an outlet arrangement could be usefull for lighting and i can see uses in a laboratoty situation but not for general perpose equipment supplies.

It is gone now. There is copy of the same in the Industrial & multiphase power plugs & sockets article, don't need two. Meggar 2005 June 29 03:00 (UTC)

splitting

This article is rather large anyway and it has almost noting on the mathematics of 3 phase.

I suggest a 3 way split three-phase: about the basic mathematics behind 3 phase three-phase electric power: about how and where 3 phase is used (ie most of what is here now) three-phase testing: basically what is now the testing section. This may be better located in a wikibook than here though i have little idea of the structure of wikibooks myself. Plugwash

ok no objections im going ahead Plugwash 21:36, 18 Dec 2004 (UTC)

ok well i've done it there is probablly still some content here that belongs on three-phase and there is a fair bit of three-phase that still needs writing. I've moved the color code information into a table beside the TOC expanded the intro section and altered the image so it fits beside the intro section. Plugwash 10:05, 20 Dec 2004 (UTC)

A good start but the article still rambles. "What's a neutral?" the reader will ask, or "Why are domestic loads single phase?" We need some a couple of simple diagrams to show the three voltage waveforms, and what we mean by "wye" and "delta" and "split phase". Something to work on during the holidays, I expect. --Wtshymanski 17:48, 20 Dec 2004 (UTC)

more two phase

"Two phase Like three phase, gives constant power transfer to a linear load." From my calcs this is not the case - can anyone confirm? --Ali@gwc.org.uk 23:48, 9 Jan 2005 (UTC)

Quick and dirty - call the phases sin(theta) and cos(theta), sin^2(theta)+cos^2(theta) = 1 for all theta, and power flow is proportional to the square of the voltage. So, two phases, 90 degrees apart in time, will also have a constant power transfer. --Wtshymanski 02:54, 10 Jan 2005 (UTC)

Rotary converter

The Wiki article rotary converter describes a completely different machine than the rotary phase converter used to make a 3-phase supply from single-phase power. This link is a little misleading. --Wtshymanski 01:52, 2 Jun 2005 (UTC)

It is written principally from the point-of-view of a traction engineer trying to convert three-phase AC power to direct current. But the rotary converter concept is fully-general; if you reversed the machine, it would create three-phase AC from DC. A similarly-constructed machine can convert single-phase AC to three-phase or vide-versa.

But you know what to do: be bold!! Please feel free to expand the rotary converter article as you see fit.

Atlant 11:50, 2 Jun 2005 (UTC)3fff

Modern technology overloading neutrals

Plugwash asks:

I've heared that this kind of thing is more of a problem in the usa due to lack of power factor correction cuircuitry. is this true?

I'm no expert but there's no doubt that modern switching power supplies seriously undermine the existing assumptions about how much current neutrals end up carrying in three-phase systems. As you doubtless realize, in the past, with passive loads (incandescent lighting, motor loads, and the like), the neutral only carried imbalance current and never more than the load of a single phase. The situation gets a bit worse with funny loads like fluorescent lamps and high-intensity discharge lamps. But now, with crappy switch-mode power supplies drawing huge current pulses but only at the peak of the sine wave (when the other phases are near zero volts), it's possible for the neutral to carry almost 3X the RMS current load of any phase wire!

One change that has definitely been made is that I think it has now become far less common to see "half neutrals" and such. Another change is that you guys over in the EU are starting to mandate power-factor correction on a lot more power supplies (although I don't think we're seeing as much of this in the US yet, but I'm sure it'll come along eventually).

I'm sure others know much more about this than I do.

Atlant 23:38, 3 Jun 2005 (UTC)

afaict half neutrals aren't allowed here in the uk anymore (i think they used to be but i'm not sure when they were phased out). I also belive that modern switched mode power supplies over here have correction cuircuitry to deal with this peak issue. However before we can add this to the article we need more solid information/sources. Can anyone here provide them? Plugwash 01:36, 4 Jun 2005 (UTC)

Regional bias?

Where the stepdown is 3 phase, the output of this transformer is ususally star connected with the standard mains voltage (120 V (in north america) or 230 V (in Europe)) being the phase-neutral voltage.

Someone embedded the following question in an HTML comment:

this comment shows rather a lot of national bias mentioning only north america and europe how best to deal with it?

-- Beland 01:57, 19 Jun 2005 (UTC)

Link to a list of systems, or place the list somewhere in this article. Crowding functional explanations with complete lists of examples isn't helpful. --Ikar.us 20:04:52, 2005-07-22 (UTC)

Confusing phrases

the output of this transformer is ususally star connected with the standard mains voltage

Can someone explain "star connected" with a sentence or two or a link to an appropriate article?

Another system commonly seen in the USA is to have a delta connected secondry with a centre tap on one of the windings supplying the ground and neutral.

Ditto for "delta connected secondry with a centre tap".

This allows for 240V three phase as well as 3 different single phase voltages (120V between two of the phases and the neutral, 208V between the third phase (known as a wild leg) and neutral and 240V between any two phases to be made availible from the same supply.

It's not clear why the third phase is 208V off from the neutral, or where the second 240V figure comes from, exactly. -- Beland 02:04, 19 Jun 2005 (UTC)

lemme think about this i think some diagrams may be needed of what star and delta are. it may be better to put them on the 3 phase page though as this one is already rather big. Plugwash 02:35, 19 Jun 2005 (UTC)

Hm, right now, there are no articles like Delta connection, Star connection... I only found Y-delta transform. As delta and star connections are a crucial part in phase systems, I would say there should be seperate articles for both. --Abdull 09:34, 22 July 2005 (UTC)

Never heard of that one

Three phase systems may or may not have a neutral wire. A neutral wire allows the three phase system to use a higher voltage while still supporting lower voltage single phase appliances. (from the introduction).

How does a neutral wire allow to use higher voltages on the phases? Thanks, --Abdull 08:51, 22 July 2005 (UTC)

If it is necessary to provide a specific one-phase voltage, then it is necessary to have this as the delta voltage, if there is no neutral wire. If the neutral wire is present, the voltage level can be chosen higher, so that the required voltage appears between phase and neutral. For example, in Austria existed 220/127V systems together with 380/220V, the latter need a neutral to supply 220V.

However, allowing a higher voltage is not the basic purpose of the neutral and may be confusing. --Ikar.us 10:47:58, 2005-07-22 (UTC)

thank you very much for that piece of information. Actually, what do you mean with the slash in 220/127V, or 380/220V? Thanks, --Abdull 11:45, 22 July 2005 (UTC)

The first number ist the delta voltage, i.e. the voltage between two phases. The second number is the star voltage, i.e. the voltage between each phase and the neutral (the first devided by sqrt(3)). --Ikar.us 11:59:48, 2005-07-22 (UTC)

so what is the main reason for chosing a 4 wire system with neutral and loads connected star over a 3 wire system with no neutral and the loads connected delta? higher voltage is the main one i can think of Plugwash 13:18, 22 July 2005 (UTC)

In a 4 wire system, you can connect incandescent lamps single-phase to neutral, and motor loads as three phases - for example, 120 V lamps and 208V motors for A/C ( in North America) or 240 V lamps and 415 V motors ( 240 volt countries). The advantage is that you don't need two systems at different voltages for lighting and power loads. I remember being troubled by the single-line diagrams for station service power of the Owen Falls Dam generating station extension till I realized...no lighting transformers! Lighting loads and motor loads all came from the same motor control center. In Canada, if you have a 600 V 4 wire 3 phase system, you can buy HID ballasts rated 347 V and they have a warranty, whereas 600 V ballasts aren't warranted by the manufacturers. --Wtshymanski 15:57, 22 July 2005 (UTC)

[adding my already written answer before reading Wtshmyanski's one]

One simple advantage: A one-phase circuit needs just one fuse in the phase. If it is delta-connected, it needs two fuses. In the case of real fuses (instead of circuit breakers), it is problematic that they aen't coupled.

Concerning power capacity, a 3-phase device can consume three times the power of a one-phase device, with same voltage and ampere rated components and lines. In delta-always-settings, the factor is only sqrt(3). So the same voltage level can accomodate a wider range of application needs.

Note that the four wire system doesn't mean that really all four wires have to be present (which would somewhat countervail the capacity gain). If the device consumes equal currents in all 3 phases, the neutral wire doesn't have to be present at all. The phase components can be star connected with open star point. If the currents aren't equal and the neutral wire is present, the sum of the 4 currents never exceeds 3 times the maximum current in one. This allows thrifty dimensioning of the lines.

--Ikar.us 16:19:29, 2005-07-22 (UTC)

constant power

I thought about the following statement from the article: Three phase has properties that make it very desirable in distribution. Firstly all three wires carry the same current. Secondly power transfer into a linear balanced load is constant.

the power transfer statement was some sort of odd to me, until i came up with the following:

We have three phases

$i_{1}(t)={\hat {i}}\cos(\omega t)$

$i_{2}(t)={\hat {i}}\cos(\omega t+120^{\circ })$

$i_{3}(t)={\hat {i}}\cos(\omega t+240^{\circ })$

Imagine a powerline system with star connection. We have a (nearly) evenly distributed resistance on all three phases, that is:

$R_{1}=R_{2}=R_{3}=R$

Imagine a big city with thousands of households all having random electrical machines at random phases in use, so in general you can think of three resistances of nearly the same size with negligible aberration among them.

Now, if we want to take a look at the time behavior of electrical power within the three phase system, we would say:

$p(t)=u(t)\cdot i(t)=R\cdot i^{2}(t)=R(i_{1}^{2}(t)+i_{2}^{2}(t)+i_{3}^{2}(t))$

$p(t)=R\cdot {\hat {i}}^{2}(\cos ^{2}(\omega t)+\cos ^{2}(\omega t+120^{\circ })+\cos ^{2}(\omega t+240^{\circ }))$

With the help from trigonometric identities (that is power-reduction formulas), we will have:

$p(t)=R\cdot {\hat {i}}^{2}({1+\cos(2\omega t) \over 2}+{1+\cos(2\omega t+240^{\circ }) \over 2}+{1+\cos(2\omega t+480^{\circ }) \over 2})$

480° equals 120°.

Next, we can use Angle sum and difference identities:

$p(t)=R\cdot {\hat {i}}^{2}{\bigg (}{3+\cos(2\omega t)+\cos(2\omega t)\cos(240^{\circ })-\sin(2\omega t)\sin(240^{\circ })+\cos(2\omega t)\cos(120^{\circ })-\sin(2\omega t)\sin(120^{\circ }) \over 2}{\bigg )}$

Sorting it all, we will have:

$p(t)=R\cdot {\hat {i}}^{2}{\bigg (}{3+\cos(2\omega t){\Big (}1+\cos(240^{\circ })+\cos(120^{\circ }){\Big )}+\sin(2\omega t){\Big (}\sin(240^{\circ })+\sin(120^{\circ }){\Big )} \over 2}{\bigg )}$

Actually, ${\Big (}1+\cos(240^{\circ })+\cos(120^{\circ }){\Big )}=0$ and ${\Big (}\sin(240^{\circ })+\sin(120^{\circ }){\Big )}=0$, so we end up with:

$p(t)=R\cdot {\hat {i}}^{2}{\Big (}{3 \over 2}{\Big )}={3R{\hat {i}}^{2} \over 2}$

Although we started to look at the behavior of the electrical power over the time, we finally ended up to find out that in a three phase system, power is time-invariant, constant - which is good for a power plant (isn't it?).

I hope I didn't make a mistake. In my eyes, the article is missing some formulas, and if someone wants to give the above calculation a final touch, go ahead, it'll be great to put it in the article. --Abdull 14:25, 23 July 2005 (UTC)

That means time-invariant within one period? Perhaps this should be stated more clearly, also in the already existing sentence. Readers could wonder how three-phase power can influence how loads are switched on and off. --Ikar.us 08:59:27, 2005-08-02 (UTC)

Hi Ikarus - once again, take a look at the last expression:

$p(t)=R\cdot {\hat {i}}^{2}{\Big (}{3 \over 2}{\Big )}={3R{\hat {i}}^{2} \over 2}$

the t in p(t) can be 5 seconds, 12 seconds... any point of time. It turns out there is no "t" in the expression on the right side, therefore p(t) is constant at any point of time. It is time-invariant within one period, so to speak. --Abdull 12:10, 2 August 2005 (UTC)

It is time invariant provided the load stays the same. obviously if devices are turned on and off that will affect the power flow but there is no constant oscillation like there is with single phase transmission. Plugwash 01:24, 1 April 2006 (UTC)

Phase converters

I started a Rotary phase converter article that discusses rotary phase converters in general. I changed te link in the phase convertser section of this article to opint to that new page. The previously referenced page discusses rotary converters in general and made little relation to phase conversion (making of third phase). I hope that this change is acceptable and would like to ask for contribution to the Rotary phase converter article.

Thanks! Ichudov 19:41, 12 January 2006 (UTC)

User:65.184.166.57 added something about energy storage being required for phase converter operation. I think the revision by User:Atlant improved what the previous editor was apparently trying to say, but I don't think the original addition is correct. I think that energy storage is needed to produce a phase shift and is unrelated to the discontinuous vs. continuous power flow. --C J Cowie 15:15, 18 January 2006 (UTC)

I think that energy storage is needed to produce a phase shift and is unrelated to the discontinuous vs. continuous power flow.

Well, both, actually, they're sort of two sides of the same coin. If you think about a hypothetical single- to three-phase converter without any energy storage (imagine just three voltage converters that could instantaneously convert X volts in to Y volts out), then during the zero-crossings of the single-phase input waveform, the voltage converters would have no input voltage to convert to the three phase outputs! So a converter must store energy to continue outputing voltage during the zero crossings of the input waveform.

Another way to look at this is to say that the input single-phase waveform is time-shifted (~phase-shifted) to form the three output phases. But the time shifting process is just another cloak for energy storage.

Atlant 17:40, 18 January 2006 (UTC)

Single Phase to Three Phase

I want to convert single phase to in 'three phase', any one have solution about this matter?

I think the article discusses this (otherwise, one of our articles does; Google with "three phase site:en.wikipedia.org". But the usual solution today is an electronic converter. In t he old days, a motor-generator set or rotary converter was used.

Just curious: what application are you supporting that needs three-phase power? Usually, the serious applications are too big to conveniently power from a single-phase supply.

Atlant 12:55, 11 February 2006 (UTC)

The rotary phase converter article describes a relatively inexpensive "do-it-yourself" method. This method is often used by metal working hobbyists and others who buy used machine tools with three-phase motors. To operate a single three-phase motor you might consider using a Variable Frequency Drive. Newer small models accept either single-phase or three-phase input power and produce three-phase output power with provisions to change the frequency to adjust the speed of a three-phase motor. Some models even have a voltage multiplier circuit to accept 120 volt single-phase input power and operate a 240 volt, three-phase motor. Some older models that might be found on eBay will accept single-phase input power and operate reliably with a load current that is about half the normal rating. If you download the instruction manual before buying, you can determine the capability in advance. --C J Cowie 15:12, 11 February 2006 (UTC)

Color Codes

Are the color codes for North America correct? I thought L1=Black, L2=Red, and L3=Blue The page is currently showing L1=Red, L2=Black, and L3=Blue.

That's how they were, but 70.65.132.11 changed them (see here). Any reference(s) for the correct colours? --Evan C (Talk) 01:03, 1 April 2006 (UTC)

Canadian code rules don't give different color codes for different voltage classes. Isolated 3-phase circuits use orange, brown, yellow for A/B/C phases ( rule 24-208 (c). Non-isolated systems (referenced to ground) use red, black, blue (A/B/C) (rule 4-036(3)(c)). --Wtshymanski 16:40, 22 March 2007 (UTC)

Why did you remove the 208V from "Connecting phase-to-phase"? I think it's a helpful reminder to let people know what we're talking about, at least in the US (and it said "US"). More generally, I think it's helpful to include the voltages as a reminder and a convenience to the user... Also, it seems silly that US is listed as B/O/Y and Canada as O/B/Y. Presumably in neither case is the order significant, but it seems weird for them not to be consistent? jhawkinson 16:45, 22 March 2007 (UTC)

I can't find my office copy of the US NEC so I can't correct the US color codes (if they have in fact been vandalized) It's NEC article 517.160, if anyone as a US code handy. (Just checking at http://www.iaei.org/subscriber/magazine/02_f/johnston.htm amd that gives O/B/Y.) This illustrates the problem with Wikipedia - nobody gives references! I took out "208 V" because it was wrong - the single-phase voltage is NOT 208 V in the US and not 400 V in Europe. The sentence reads better without all the numbers, and the whole point is beaten to death earlier in the article. Besides, there's also 347/600, 277/480, 14400/24940, etc. - why stop enumerating at just two cases? --Wtshymanski 17:13, 22 March 2007 (UTC)

Sorry, I meant to come back to this last week and it slipped my mind. 517.160(5) indeed says, "The isolated circuit conductors shall be identified as follows: (1) Isolated Conductor No. 1 — Orange; (2) Isolated Conductor No. 2 — Brown; For 3-phase systems, the third conductor shall be identified as yellow." But article 517 is "Health Care Facilities" -- isn't this a bit too specialized? I don't think the NEC mandates the specific colors used in the US (this based on searching my PDF full-text of it). It does mandate that the high-leg conductor shall be orange in delta system (110.15, 230.56). But it doesn't specify Black/Red/Blue or Orange/Brown/White at all — I assume that is convention? Actually, I guess there's one more bit: 408.3(E) (bus-bar phase arrangement) requires the B phase (in the middle) to be the high-leg, and thus orange. So that permits B/O/Y or Y/O/B but not O/B/Y. Is there any reason to associate the isolated conductor numbers with position? 517.160 goes on to indicate that orange must be the grounded conductor.

In 240V delta systems I have typically seen Black, Orange, Red, with Orange on the high leg to meet NEC. I've never worked on grounded 480 delta systems so I have no idea what the colors are there.

Should there be a mention of the requirement to identify neutrals? Often the neutral on 480V is gray to distinguish it from the 208Y120 neutral.17:24, 29 July 2007 (UTC)

In re 208V, I guess the problem is ambiguity. The text was "Connecting between two phases provides √3 or 173% of the single-phase voltage (208 VAC in US; 400 VAC in Europe)"; it is not saying that the single-phase voltage is 208V, it's saying that 173% of single-phase is 208V. In my view, it's important to include the number 208V several times in there, because it doesn't tend to be ingrained-in-the-brain for non-practitioners, and it really helps in understanding and giving examples to aid in learning. Unless you object, I'll put back 208V and try to eliminate the confusion about whether it is talking about phase-to-phase (yes) or phase-to-ground (no). jhawkinson 16:15, 27 March 2007 (UTC)

Please don't list the phase-to-phase voltages in the affected section; as I said above, they are different depending on which system is used. The actual numbers don't matter so much as the idea that the phase-to-phase voltage gives another option for powering single-phase equipment. --Wtshymanski 17:45, 29 March 2007 (UTC)

As best I can tell, your argument is that because there are different 3-phase systems, it is not a good idea to give an example of a 120/208Y system, even though it is the common case? I don't buy that argument, I do think that provide solid examples really aids in understanding. Anyhow, I don't want to get into a revert war, so I won't make this change, but I think we can do better than what is here now. jhawkinson 22:10, 29 March 2007 (UTC)

This page is still incorrect for Canadian colour codes. The Canadian Electrical Code clearly states A phase = Red, B phase = Black, C phase = Blue, it is NOT black blue red! CEC rule 4-036 (3) —Preceding unsigned comment added by 24.64.125.122 (talk) 20:03, 17 August 2008 (UTC)

I think I've wandered into an edit war. I corrected this colour code for Canadian three phase from (black, red, blue) which is wrong, to (red, black, blue) which is straight out of my copy of the code right in front of me, and it was undone (and made wrong again!) without comment or explanation by --Wtshymanski in edit: http://en.wikipedia.org/w/index.php?title=Three-phase_electric_power&diff=237414020&oldid=237355282 Can we argue about this here rather than swapping 'undo's? This is all the more mysterious because you said yourself: "Non-isolated systems (referenced to ground) use red, black, blue (A/B/C) (rule 4-036(3)(c))" in this very discussion. --TonyGraySchneiderElectric —Preceding undated comment was added at 16:58, 15 September 2008 (UTC).

argh. When the Alzheimer's sets in I won't even notice. 4-036(3)(c) does say red, black, blue, even though single-phase cables are black/white. --Wtshymanski (talk) 00:08, 16 September 2008 (UTC)

Many thanks for your contributions - you're clearly very knowledgeable - it was just an accident. All the best, TonyGraySchneiderElectric (talk) 17:25, 16 September 2008 (UTC)

A Laymen's Introduction Perhaps?

First I want to say that this article was obviously written and contributed to by people who really know what they’re talking about. The depth of the technical detail is impressive.

However, coming in as a layman rather than an electrical engineer, electrician or mathematician, I was lost almost from the beginning, looking for a simple explanation of what three-phase as compared to a ‘normal’ electrical supply was. I have seen this issue before in Wikipedia articles—experts provide great in-depth detail without realizing that the average user may be looking for a concise, high-level explanation of the subject that can be quickly read and understood to a limited degree (drive-by users I call them). I doubt most people have more than a minimal understanding of AC power generation and transmission to begin with, so by immediately jumping into pretty technical details, a majority of readers may be left behind without gleaning even a basic understanding of the subject. For this article, I think it would be great to have a short introduction that in simple language explains, for example, why a three-phase supply is better suited to motors for industrial duty, while most household appliance motors can get by with single-phase that's usually supplied. peterr 02:55, 15 October 2006 (UTC)

It's in there, but maybe it should be moved to the top. The whole point of having a 3-phase system is to run AC induction motors. Or stated more clearly: the whole point of the Tesla Polyphase System installed by Westinghouse Corp is to operate Tesla's polyphase AC motors. These are brushless motors which require two or more AC circuits with differing phase to create a rotating magnetic field that drags a copper/iron cylinder into rotation. No other reasons for having multiple AC phases make much sense, since other types of loads don't require 3-phase, and smoother DC rectification is a historically later benefit (Rectifiers didn't even exist in 1896 when Westinghouse Corp first started installing the Tesla Polyphase System.) --Wjbeaty 02:24, 21 October 2006 (UTC)

I realize it’s all in there and well-explained, and the introductory sentence does mention AC induction motors. But the very next sentence is “Three-phase systems have at least three conductors carrying voltage waveforms that are 2π/3 radians (120°,1/3 of a cycle) offset in time. In this article angles will be measured in radians except where otherwise stated”. This reads like a textbook, and in my opinion could scare away a reader with no concept of waveforms that measure 2π/3 radians, or those not prepared to use units other that radians for angle measurements (when specifically told to do so).

The article titled “Three-phase” has as its introductory sentence the second sentence of this article. The other article too jumps straight into technical concepts and mathematics, rather than providing a quick overview of AC power, or at least a link to a layman’s article on the subject. (BTW I think these two articles should be combined—there is redundancy, and I’m not convinced of the usefulness of the shorter one that provides strictly a definition without touching upon application. For example if I wanted to find out what a bolt was, I would be pleased to have the same article that describes it as cylindrical and threaded go on to explain its primary use as a fastener.)

A waterfall that from the top down moves from high-level, easy to comprehend concepts for the layman, down to hard-core technical details for the initiated, is the structure I’m advocating. There may exist already guidelines on this, and certainly there are a multitude of other articles that would benefit from friendly introductions to their complex topics. I’m not picking on this article in particular; rather, because of its quality and wealth of information, I think it makes a good example of what a great Wikipedia article could be. Writers on technical topics should consider the possibility that much of their audience is being directed to their articles from mainstream searches, not from footnoted references in scholarly publications. Wikipedia should be not only accurate and comprehensive, but accessible to users of all educational backgrounds and fields of expertise. Introducing an article by supplying a useful, high-level definition in a non-intimidating manner may interest and encourage a user to read on to the nitty-gritty if he chooses. If he is satisfied with only the high-level definition, then the article has still served its purpose. Nothing is gained by anyone when a reader is scared away by immediate immersion into complex or esoteric discussion, and I don’t think it is in the spirit of Wikipedia to be, or appear to be, elitist.

From laymen looking for one-minute definitions to professionals seeking in-depth answers, people of all backgrounds should find Wikipedia the best all-around encyclopedic resource on the Web. Contributors of the highest caliber, however, must assume that many readers of their articles may be completely new to the topics. Detailed, technical information drawn from accumulation of knowledge and wealth of experience is of course invaluable to other professionals and students, those readers of the ability to comprehend such. However, there is should exist the responsibility to provide for the most casual of information seekers as well, those who enter having no knowledge of the topic whatsoever. These users deserve the best the contributor can provide in the manner of a concise, easily-understood definition or overview of the topic, and the contributor may take as much pride in creating this as in the sharing the detailed information that follows. It may well be that a great majority of readers require that high-level explanation, and the ability of an expert to distill the complexity of their topic into this concise, layman-friendly introduction speaks to his professionalism and generosity.

To conclude this overlong “comment”, although an introduction of sorts may be in there somewhere, it’s not what I envision for the layman who just wants to know if his toaster runs on three-phase current.

BTW from what else I’ve read regarding the adoption of three-phase AC generation and transmission, it was due to more than just its ability to start Tesla’s AC motor turning, but I get the feeling you don’t believe the other arguments for the system. I’d be interested in what makes your opinion on this so strong. I’m a layman myself, but this fascinates me, so I’ll try to keep up with whatever you want to tell me. And thanks in advance!

peterr 02:44, 23 October 2006 (UTC)

Phase Converters...comments needed on Solid State Digital Phase Converters

In doing some research on phase converters, it can all be rather confusing when trying to choose which are better than others, particularly looking at 10HP models, and intrigued of the new phase converter on the market by Phase Perfect which introduces a Solid State Digital True 3 phase converter. Intended to be a 3rd choice as opposed to rotary and static. Wondering if anyone has comments on this new device, seems to be revolutionary to Phase Converters? —The preceding unsigned comment was added by Mag43 (talk • contribs) 00:59, 5 December 2006 (UTC).

Some sections of intro should be deleted

The subsections in the intro titled "Star connected systems without neutral" and "Unbalanced systems" should be deleted because they were copied vebatim from the more in-depth three-phase article. These paragraphs are only comprehensible with a theoretical intro given first. However, this "how and why" article does not have one. Hanjabba 00:49, 20 March 2007 (UTC)

Way Too Technical and Obscure

I'm a pretty well educated guy. I know my way around a circuit board. But I couldn't make heads nor tails of this article. What does three-phase mean, for gosh sakes? That's what Wikipedia is all about. Save the math for the engineering classroom. Give us some basic "stuff".Scott Adler 11:04, 7 April 2007 (UTC)

Would you look at the paragraph I added just now? Is this in the right direction? It's hard for fish to define water, you know; your persepective from the shore is very useful. We could build up to the math...slowly. --Wtshymanski 23:26, 7 April 2007 (UTC)

I'm not Scott Adler, but that looks pretty good to me.

Atlant 16:53, 9 April 2007 (UTC)

Why three-phase

I know this sounds simple but can anyone describe the reason for, and generation of the three-phase supply as compared to a single phase supply? —The preceding unsigned comment was added by 62.140.211.130 (talk) 08:35, 9 May 2007 (UTC).

Single phase systems only deliver power roughly 2/3 of the time. This is tolerated where only small or modest loads need to be supported, because the simplification in wiring compensates for the inefficiency. However, where larger loads are present, a multi-phase system which delivers power nearly all of the time is preferable.

Another factor is the issue of motors. Single-phase induction motors are not inherently self-starting and require some additional means (such as an auxiliary winding) to get going. Multi-phase motors, on the other hand, are not only self starting, but they are typically smaller and lighter than single-phase motors of the same horsepower rating because they do not have to overcome the "valleys" of a single phase supply.

While it is theoretically possible to build a system with any number of phases that divide evenly into 360 degrees, Nikola Tesla always believed, and Charles Steinmetz subsequently proved mathematically that the three-phase system offers the best balance of performance and cost.

--Melvan 77 Melvan77 12:50, 24 October 2007 (UTC)

"NEC does require color code"

Err, Wtshymanski, can you substantiate this a bit better? While the US NEC does require coloring, and does mandate specific colors for ground and neutral and high-leg delta systems, it does not mandate particular colors for other applications. When I looked at the table recently, I felt like it was too easy to assume that BLACK/RED/BLUE were universally standard phase colors for 120/208V. With your recent change this problems seems to've gotten worse. What was your thinking in removing this?:

However, the current National Electrical Code (2005) does not require any color identification of conductors other than that of the neutral (white or white with a color stripe), the ground (green or green with a yellow stripe), and, in the case of a High Leg Delta system, the High Leg ("shall be durably and permanently marked by an outer finish that is orange in color or by other effective means"). (NEC 110.15).

Thanks. jhawkinson 12:11, 26 May 2007 (UTC)

These aren't phase colors. The copy of NEC that I have access to is at the office right now. I'll have to find the rule. The Canadian rule is 4.036 at least in my 1983 code...have to check the current edition at the office. --Wtshymanski 02:53, 31 May 2007 (UTC)

I don't understand your response. The NEC does not require phase coloring. The prior wording did not specifically make a statement about phase coloring as opposed to other coloring. I'm going to restore the above cautionary wording because I think it was helpful. I'm confident you won't find a requirement for phase coloring in the NEC, but if you do, feel free to revert. jhawkinson 20:22, 31 May 2007 (UTC)

Bill, would you please respond here before making further edits and reverting mine? I'm happy to discuss or be shown to be wrong, but I don't think it is reasonable for you to revert edits without explanation when you have been asked explicitly. I think article 517 is so obscure as to hardly deserve the prominence of mention on this table. It only applies to health care, a very small portion of the wikipedia community. The other uses of B/O/Y coloring far exceed the 517 use.

Also, 517 is about "isolated power systems," not "isolated ground." The former means transformers (or equivalent isolation devices), the latter means "homeruns of green wires." I do think it is important to note the unreliability of color codes prominently above the table. Even though it is mentioned in a footnote, I think, for safety's sake, it deserves more. I am not an expert, but I do not think it is common for local regulations to amend the NEC on color coding. What is common is for "common practice" to vary from region to region, or even site to site. jhawkinson 19:03, 5 June 2007 (UTC)

517 is the only place the US NEC dictates phase colors. From what I've read on the Web up to 1975 there were NEC schemes for coloring phases. The Wikipedia is the *home* for obscure facts. What colors would you find in a US 347Y/600 V installation? For that matter, what about 230V, 2300V, 4160V, 13.47 kV, etc. etc. - there are many more voltages than 120/208 in use, and it's useless to imply that the listed colors have any voltage significance *at all*. I see on the Web that Juneau, Alaska has implemented their very own local color codes - it must make it hard to buy cables that comply, and by using the same code for a 480V system as the NEC mandates for an isolated power system, it completely screws up the intention of that part of Article 517. Disproportionate discussion fo the US NEC is not appropriate for a general article on three-phase power ( arguably the whole color code nonsense should be dropped anyway, since its not fundamental and not even useful). Finally, Wikipedia is not a safety manual and must never pretend to offer safety advice lest the lawyers sue Wales & Co. into bankruptcy. Safety notices on stupid things you can do with electricity would easily double the current size of the English Wikipedia alone. --Wtshymanski 17:50, 6 June 2007 (UTC)

I agree 517 is the only place the NEC dictates phase colors (I'd think that would be clear from my comments in March). That Wikipedia is the home for obscure facts does not mean that the obscure facts should lead the common ones. Almost any use of B/O/Y is more common than the 517 usage. B/O/Y for 277/480, B/O/Y for a seperately derived 120/208Y system, etc., etc. Perhaps you could offer a more clear citation to your concerns about Juneau, AK. I think the color codes are actually an important part of this article, and, for instance, if one is trying to find out about color codes for electrical wiring, the Color codes article takes a reader here.

I suppose the question is "what is disproportionate?" This change was added in 37447436 in Nov 2006. I think it should stay. You think it should go. Who decides? I would say we favor precedent.

I don't find your argument about safety messages compelling, but here you have precedent on your side and I'm less inclined to spar over that point.

It is, however, simply incorrect to say that B/O/Y is "Mandatory for isolated power systems." It is "Mandatory for isolated power systems in health care facilities," and that is a very very different thing. Non-healthcare B/O/Y uses far exceed health care isolated power uses. jhawkinson 23:26, 7 June 2007 (UTC)

Well, then, let's mark B/O/Y as "Mandatory for isolated power systems in health care facilities and commonly used for 480/277", which it already says in the footnote. But the whole point of the 517 rule then escapes me...what's the point of a special color code for an isolated system, which is the same as the standard color code for a non-isolated power system at 480 V? The harmonized British/European color codes are even worse - it takes a strong light and clean cables to distinguish brown from grey from black.

What are the color codes in the US for other voltages, e.g., 2300, 4160, 13.47, etc. etc? There's even some 600/347 in the US, and I understand the oil fields use 800 V. I think it is at best mislead and at worst just wrong for the Wikipedia to imply that there's any standard to the assignment of voltage levels to color codes when it plainly varies depending on local practice. I've even found some specs that call for purple and other colors in 3-phase wiring. The Canadian rule gets rid of all this nonsense (though we have the isolated system color code too, at least ours isn't the same as non-isolated systems. Though the Canadian rules have the phase sequence different from the US. --Wtshymanski 01:28, 8 June 2007 (UTC)

I think we would be better off labelled B/O/Y as a "US Alternative" coding, and mentioning both the 517 and 477 uses in the note, esp since the 517 use is less common. You are asking what the purpose of a piece of the NEC is? Code evolution is complex, political, and not always sensical...

Why did you remove the text about the orange triangle marking for isolated ground? jhawkinson 13:38, 8 June 2007 (UTC)

Digital Phase Converters

See Dr. Larry Meiners "Phase Converter Technology Overview" http://www.phaseperfect.com/files/phasewhitepaper.pdf Soothsayer2 (talk) 16:04, 28 February 2008 (UTC)

can i connect 3phase 380 v 50 hz motor to 480 v 60 hz supply

can i connect 3phase 380 v 50 hz motor to 480 v 60 hz supply —Preceding unsigned comment added by 41.233.31.153 (talk) 12:58, 3 August 2008 (UTC)

2 and 4 phase power

I wish to see information mentioned on 2 and 4 phase power as referenced in http://www.nordichardware.com/news,8295.html

Thank you. Habanero-tan (talk) 22:21, 10 December 2008 (UTC)

Then add it? Ironholds (talk) 13:42, 23 January 2009 (UTC)

Power availability in each country

I think some one can summarise various power situations available in various countries across the globe with details like Voltage, single phase & three phase Frequency, Power plug type Thank you, Vijai Shankar Raja (talk) 00:15, 16 March 2010 (UTC)

Look at Mains power around the world. --Wtshymanski (talk) 13:02, 16 March 2010 (UTC)

Linear Balanced Load

Can someone explain "linear balanced load" in layman terms for the public? Thank you. Yeokaiwei (talk) 06:53, 14 October 2010 (UTC)

"Linear" -voltage and current vary in strict proportion and if eitehr is zero, the other is zero. "Balanced" means all three legs the same. I would have thought the article explained this. --Wtshymanski (talk) 13:03, 14 October 2010 (UTC)

"Interesting" example?

From Three-phase electric power#Three-phase loads: "An interesting example of a three-phase load is the electric arc furnace used in steelmaking and in refining of ores."

I question the use of "interesting" to describe this example. It is a form of non-neutral/editor's-opinion (see WP:EDITORIAL). My {{cn}} tagging for justification of this description was removed with the comment "interesting because it's not a motor". But this is one of many non-motor examples in this very section of prose. On that basis, it is not exceptional at all, so I removed the word as an objectively incorrect assessment of that situation (with edit-summary saying as much). It was re-added (by the same editor who disputed my CN) with "Really?". Yes, really. Need some others' opinions to resolve this dispute here. DMacks (talk) 18:21, 2 September 2011 (UTC)

Hi. I've come in response to the 3O request. Yes, the word "interesting" is not appropriate, just on a "says who?" basis. Since the section has no cites (a situation which it would be good to rectify, BTW), there's no justification for it including anything which might be a matter of opinion. --FormerIP (talk) 18:40, 2 September 2011 (UTC)

Oh for heaven's sake. Arc furnaces are fascinating gadgets. Suddenly a very mild variation from the usual plonkingly dull prose for which Wikipedia is so justly famous becomes a matter for the ArbCom. --Wtshymanski (talk) 19:09, 2 September 2011 (UTC)

The wikilink is there, so readers can click through and find out about how fascinating arc furnaces are if they want to. The dispute may be tedious, I can't possibly comment. But DMacks has it right. --FormerIP (talk) 19:16, 2 September 2011 (UTC)

"Write a page full of dither, no-one notices; but pick one word and get a curb stomping"--Wtshymanski (in edit-summary for 19:09 comment)

Very well: there is also lots of good neutrally written content in this article that seems factually correct based on my understanding (albeit often substantially uncited, as has been tagged for years). DMacks (talk) 19:19, 2 September 2011 (UTC)

You left out "Ergo, Wikipedia rewards and encourages bad writing." It does, you know. --Wtshymanski (talk) 19:35, 2 September 2011 (UTC)

No, I chose not to state why I don't believe, and I am getting offended that you keep thinking you know what I and others think. Stop it. DMacks (talk) 19:38, 2 September 2011 (UTC)

Wtshymanski, I think what makes for good or bad writing may be in the eye of the beholder. Being an encyclopaedia, WP normally encourages a neutral, factual tone. It's contents should reflect established facts or representative expert opinion. The opinions of editors are not included, and I think most editors would say that including them comes across as unprofessional.

I can't believe this is worth arguing over, but DMack's edit is in line with normal WP practice. --FormerIP (talk) 19:56, 2 September 2011 (UTC)

Yes, yes it is. There's no argument. --Wtshymanski (talk) 20:01, 2 September 2011 (UTC)

Now we're getting somewhere: [1]: it's interesting to you because you say a specific way it's different from all the others. Why is 3-phase used in this situation, given that it doesn't need rotational-direction or fluctuation-reduction? That would allow the fact to be written tied to other themes in the article, in particular, that this type of power has certain specific advantages. DMacks (talk) 21:09, 2 September 2011 (UTC)

Wtshymanski: Just in case you haven't noticed, you've reverted three times now. Any more could land you with a block. The sentence currently reads: "One example of a three-phase load is the electric arc furnace used in steelmaking and in refining of ores". Can I suggest that nothing else is now added to that without discussion on the talk page first and, preferably, reference to sources? --FormerIP (talk) 21:20, 2 September 2011 (UTC)

I am too busy spitting out bloody teeth to carry on with this now. --Wtshymanski (talk) 01:08, 3 September 2011 (UTC)

'Colour' or 'Color'?

Several editors keep changing the spellings in the article from British English to US English and back again. One editor claimed that the spellings used in March should be used or, "that was how Tesla spelled (sic) it" (Invalid arguments in both cases). Another changes the spellings to British English citing the policies of WP:ENGVAR and WP:RETAIN. Correct and good argument, not no cigar. Both of those policies require that the variant of English used for an article must be the one in which the article was originally written (not how it was written in March or how Tesla would write it). The original article was relatively language neutral apart from one US English term, 'wye' (the British English term being 'star'). Thus the original article was written in US English and thus that is the variant that rules. Indeed the spelling 'color' was introduced a bit later (ironically when introducing the old British colour code). The cited policies require that the English variant is not changed, "... without a broad concensus" - and that just ain't gonna happen.

Though it pains me to say it: as the original article was written in US English, those are the spellings that must appear in the article.

Symbols or numbers

I don't agree with this edit (especially as it is the second time it has been applied after being reverted). A numerical example is much clearer than algebra to my mind. It does not really matter whose numbers are used, but I think that Wtshymanski may be right that high-leg delta is unknown in 240/230 V countries. I have certainly never seen it in a European country. SpinningSpark 23:03, 16 November 2012 (UTC)

Paraguay has 440-220 center tap delta. Japan has 200-100 delta. If we express it in terms of algebra, we don't infuse country specific bias. I substituted with 200/100, because they're cleaner number than 240/120. To substantiate whats used by what countries, what they use/what they don't use require citation, but expression in in algebraic terms eliminates that. Cantaloupe2 (talk) 04:30, 17 November 2012 (UTC)

Three-wire versus four-wire / Delta versus Wye Systems copied from user quick archival

This needs discussion and copied from archives of User talk:Wtshymanski being obscured by archival.

What are you trying to get at with your comment "I have 3 wires coming out of the wall -- is it delta, or is it wye?" Number of wires at the wall is not good way to tell what you've got. It's the type of source winding that determines what kind of system you have.

If you're seeing 220v between any of the terminals, it could be a 230v delta as sometimes used in US, or it could be the 127Y/220v as used in Mexico. Delta with one of the coils center tapped could be arranged as 4W. Cantaloupe2 (talk) 22:45, 15 November 2012 (UTC)

I might have three phases on three wires. I couldn't have less than three wires for a three phase system. On the ohter hand, if I have four wires, I probably have a neutral. I think its more useful to say "three wire" and "four wire" than to experiment with typography and Greek letters. --Wtshymanski (talk) 22:47, 15 November 2012 (UTC)

It is not an experiment. Referring by the way it is fed from the transformer is an industry accepted practice. The use of neutral is optional. A three phase receptacle may have four wires. It can be L1,L2,L3+G from 120Y/208 system or L1,L2,L3+G from 230v delta system. In the latter, you could still have a neutral and have high-delta system. So, three phase systems are not classified by number of wires, but rather by the transformer source winding configuration. Does this make sense? Refer to delta/wye reference in industry here "For combination single-phase lighting and power, and three-phase power: 120/240 four-wire delta, 120/208, four wire wye, volts and 277/480 four wire wye." Cantaloupe2 (talk) 22:59, 15 November 2012 (UTC)

How it is fed from the transfomer is completely irrelevant. If you have only those three wires coming out of the wall in an otherwise completely insulated room and you can positively determine that it is a three phase supply, there is no method by which you can determine whether the transformer is star (wye) connected or delta connected. For the purposes of connecting a three phase load it doesn't really matter anyway. The only time that it does become relevant is if you require a neutal connection because it is not directly available from a delta connection. In a practical installation, the transformer is almost certain to be star connected because any mismatch in the windings of a delta connected secondary can result in unwanted currents circulating in the windings. There are, however, more esoteric connections that can avoid these. DieSwartzPunkt (talk) 16:07, 16 November 2012 (UTC)

This isn't about how it matters to the person hoking wires up. Actually, neutral can be available for delta, which is shown in one of the diagrams in the article where one of the coils is center tapped and grounded which is called "120/240 four-wire delta" in the article I linked above. In the USA, this is used in industrial setup where most loads are 230v motors with a few 120v stuff here and there. 208/120(Y) is used in offices where most loads are 120v, but may use 208v for elevator and HVAC. They both have 4 wires. Measuring phase to phase is not reliable means of identifying it, b/c 208 on high end of margin and 240v on low end of margin can end being about the same. Cantaloupe2 (talk) 20:34, 16 November 2012 (UTC)

This conversation needs to be on the talk page of the article for future referrence and edit arguments. Can somebody please move it there?

The article title appears to be about three phase systems and the system is determined by the transformer windings feeding the system. Wires are not an appropriate title to determine the "system" as already indicated by the number of variations present. We also have 3 wire wye supplies, already discussed. Some know this as "three phase four wire, one leg out". Some meters companies call it "Network". Every combination is available so the system feed terminology has to dominate. Distribution systems can be 3 wire or 4 wire and does not determine what the supply system is. BTW: Our utility discontinued 4w delta systems a few decades back as non-metering engineering staff could not understand the equipment installed by field personnel. 174.118.142.187 (talk) 02:22, 17 November 2012 (UTC)

End of copied text. Please continue discussion below. 174.118.142.187 (talk) 03:52, 17 November 2012 (UTC)

That would not be a proper neutral in the way most people understand it. If you want to be pedantic, you could create an artificial neutral from a delta secondary using three equal value resistors (or capacitors or inductors). 86.159.159.194 (talk) 16:55, 17 November 2012 (UTC)

What is the "proper" neutral the way "most people" understands it? Please cite sources. Cantaloupe2 (talk) 08:23, 18 November 2012 (UTC)

You know very well that I am talking about the neutral derived from the centre point of a star (or wye) would transformer. High leg delta systems are seldom encountered (if ever) on this side of the great pond. 86.159.159.194 (talk) 12:39, 18 November 2012 (UTC)