30A wiring advice



Given that most service comes from one, two or three stepdown transformers (single, open-delta, delta) anyway, reconnecting them into the Scott-T connection isn't much of a difference. Many commercial transformers have the center tap and one at 86% (the tap needed on the single-phase to center transformer to get the same voltage).
So, reconnecting a set of service transformers is kind of trivial when you think about it.
daestrom
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John Woodgate wrote:

See ANSI Standard C1, where the nomenclature of US electrical systems is defined. This is not a matter of opinion.

Another poster addressed this.
73, JohnW
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John Woodgate wrote:

Then a 3-phase system is half a six phase system.
John, this is just a matter of semantics. If you prefer to call the North American centre tapped SINGLE phase system "two-phase", go for it. It's your God given right. And those across the pond choose to call their centre tapped system "single phase, it is their right as well.
According to what you are saying, you take a single transformer winding and tap it in the middle, that gives you two phases. Then you should be able to tap that same winding in another spot and get 3 phase. Couple more spots and you get 5-phase.
You say the two phase system is really 4 phase system because the phase angles have to add to 360. Look at it this way. Phase 1 to Phase 2 is 90 degrees. Phase 2 to phase 1 is 270 degrees. You have to count in the same direction. You the way you are doing it adds to zero degrees.
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I read in sci.engr.electrical.compliance that No Spam
'30A wiring advice - a complication?', on Sat, 4 Oct 2003:

I agree; that's why I don't understand the violent reaction of some US people on the subject.

No, that's specious. With one winding, you have the choice of 0 or 180 degrees phase. There is no way to get 120 or 72 degrees.

Well, that's yet another way of looking at it, better than appealing to a sum of angles being 360 degrees. My point is that a 2-phase 90 degree system is unsymmetrical, unlike a two-phase 180 degree system or a 3-phase 120 degree system. A three-phase 60 degree system would also be unsymmetrical. Unsymmetrical systems of this type can be made symmetrical by doubling the number of phases, **and this can be done by means of 1:1 transformers**. This last point applies to a single-phase supply as well, with conclusions that should now be obvious.
--
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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Au contraire. A 90 degree 2 phase system is symmetrical. The whole thing transmits constant power (remember: sin(x)^2+cos(x)^2=1, and cos(x)=sin(x+90) A center tapped transformer doesn't transmit constant power, and its power is identical to a single phase non-center tapped transformer. A 3 phase system (with all phases available and used) is also symmetric.
--
-Mike

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There are some interesting {not exactly cutting-edge} variations of "legacy?" service out there. PECO lists "standard primary - unregulated alternating current, 60 hertz, nominally 2,400 volts, 2-phase, 3 wires." Con Ed lists "Two phase, 60 cycle service at 1,950 volts."
--s falke
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"legacy?"
Apparently 2 motors/loads were fairly common in Philadelphia.
Until recently, a web link on the McCombs Dam turnstile bridge in NY was described as [currently using two ~1890s] 2 motors... may have been turnstile drive and hydraulic pump.
An 1894 quote by CF Scottcreator of the "Scott-Tee" 3-2 transformation: "In considering the marked advantage of the two-phase system for distribution and of the three-phase system for transmission, it occurred to me that a combination of the two systems night secure the advantages of both..."
--s falke
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No Spam wrote:

Abraham Lincoln once asked, "If you call a dog's tail a leg, how many legs does a dog have?". His answer; "Four; calling a tail a leg doesn't make it one." Particularly in a technical field, getting the terminology wrong has caused more errors than any other single factor in my experience. As I said in a previous post, this issue is defined in the same way in various standards and in every electrical engineering text I've ever seen, and the definition is as I have explained it before. Do I have the right to call a capacitor a transformer? NO!
Every hot conductor in a power system is not a "phase".

73, JohnW
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I read in sci.engr.electrical.compliance that John Wilson
about '30A wiring advice - a complication?', on Sun, 5 Oct 2003:

You cited one ANSI standard.
I do not wish to continue this futile exchange. You are not prepared to see any other point of view than your own.
--
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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John Woodgate wrote:

I cited one ANSI standard, because it's the one I remember offhand. I have access to many others at work; this entire exchange has taken place on a weekend. If you want more references, I can supply them.
Anybody have access to a collection of IEC standards, to see what the European definition is?
In any case, most terms, including many others that are frequently misused, such as "metalclad switchgear", "circuit breaker", and so forth, are each defined in a particular standard.
73, JohnW
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Good answer. Accurate and to the point.
Unfortunately it won't change the minds of the fanatics; but you have the satisfaction of having answered the question for the rationale ones.
HR.
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On Wed, 1 Oct 2003 06:31:14 -0700, the renowned "s"

Not really. Many of us claim that two linearly dependent voltages don't represent two distinct "phases", even if one of the proportionalities happens to be -1. John disagrees.
A two phase supply with conventional 90 (or anything != n * 180, n is an integer) difference between the phases could be used in motors, as your comments suggest, or converted by a Scott-T transformer to make three-phase (or other polyphase) power. Canadian/US residential power cannot, so those who want to bring an industrial machine tool into their basement or garage have to use a static, rotary or VFD phase converter.
This has been discussed before...
Best regards, Spehro Pefhany
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<...snipped...>

That is just so wrong.
--

Larry Wasserman Baltimore, Maryland
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(Lawrence Wasserman) wrote:

Maybe you could explain?
-- Regards, Doug Miller (alphageek-at-milmac-dot-com)
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It MUST be two phase between the two hot wires, because if it was in one (the same) phase then the heating element would not heat up.
- +ve 120V - - - - - - - - - -ve 120V
+
- +ve 120V - - - - - - - - - -ve 120V
= no potential difference between the two hot wires and so no current flow. Waves are in a single common phase.
- +ve 120V - - - - - - - - - - - - -ve 120V
+
- +ve 120V - - - - - - - - - - - - - - -ve 120V
= 180 deg phase shift, 240V potential difference at peaks therefore current flows therefore heater heats up.

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In terms of maths/physics/engineering you are clearly correct.
In terms of the US electricity supply industry, "2-phase" is a specific jargon term which applies to only one 2-phase system. In the UK electricity supply industry, the common US scheme was called 2-phase (but is long obsolete and was never common).
--
Andrew Gabriel

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Joe 90 wrote:

Lets go to the understanding of how it heats up and avoid the controversy that surrounds what you label it. Consider: + - + - A--Battery1--B--Battery2--C Let each battery provide 120 volts. A to B = 120v; B to C = 120v; A to C = 240v or in other words, a simple series circuit (the circuit being completed by the voltmeter). Either battery can be used independently of the other, providing 120v DC, or they can be used in series to provide 240v DC.
Now, substitute the secondary of a center tapped transformer for Battery1 and Battery2. Again, it is a simple series circuit. Either half of the secondary can be used independently of the other half, and provide 120v AC, or the two halves can be used in series to provide 240v AC.
In the US, the dryer uses points A and B (or B and C) to provide 120 volts for lighting, timer circuit, motor circuit, electronics, and points A and C to provide 240 volts to the heating coil circuit. The dryer does not give a rat's ass what we call it - single phase, two phase, split phase or anything else - as long as it "sees" the required voltage at the necessary current.
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Whereas On Wed, 1 Oct 2003 10:43:11 +0200, "Joe 90"
, I thus relpy:

It is Vab= -Vbc0, Vac$0V. Note the -Vbc, it is 180 degrees out of phase of Vab.

Don't forget there is a motor and a timer in the dryer also, and they need 120V.

They seem to allow it, so it is okay.

--
Gary J. Tait . Email is at yahoo.com ; ID:classicsat

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On Wed, 01 Oct 2003 16:45:12 -0400, the renowned Gary Tait

And generally a light bulb. Since the neutral only carries an amp or two, it could probably be recreated with a compact 230:120 control transformer or autotransformer, but I have no idea what getting that intalled to code for a Swiss residence would involve.
Best regards, Spehro Pefhany
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replying to John Woodgate, Albert wrote: John, THANK you for yr Comments. can you tell me when cable ratings are calulaged for say 10mm2 twin and earth do they apply to the WHOLE cable, or just per single Conductor? If at all poss please Emil your reply. Many many thanks. albert
--
for full context, visit https://www.homeownershub.com/maintenance/30a-wiring-advice-478049-.htm



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