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

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

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.

I read in sci.engr.electrical.compliance that No Spam wrote (in ) about '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.

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

I read in sci.engr.electrical.compliance that John Wilson wrote (in ) 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.

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.

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.

"John Woodgate" wrote >

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

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

It depends how you cost your free time. If you were going to be earning money during the time you were DIYing it might make more sense to get someone else to do it. If you were on the other hand doing nothing else at the time, then you've effectively earned the electrician's fee for yourself by doing it yourself. In between those two extremes there's a cost-benifit tradeoff - will you pay someone to do the job to increase your leisure time?

When doing personal projects, the taxation regime enters into it. If I gross 50 Euros/hour and work an *extra* hour in Europe I might only net 25 (assuming a *marginal* rate of 50%- the average rate will be lower, of course). If I pay the electrician (who has his or her own taxes to pay) more than 25 Euros for an hour's work, I'm in a loss position compared to not working the extra hour and doing it myself. If he's charging 50 then I can take 1-1/2 hours to do that job and buy a few tools and still come out even (and get to keep the tools). If it's a business expense, then the taxation considerations disappear and I can use the 50 Euros figure.

As taxation is (was?) highest in the Scandinavian countries, that may account for the popularity of DIY-type stuff like Ikea. Here in Canada, this problem is solved in the home renovation field by a large contribution from the underground economy, which evens out the tax thing- the $1000 cash after tax to put a carpet down (less expenses) goes right into the pocket of some guy with a pickup and a free weekend. Not everyone does it, but enough that it's a factor.

Best regards, Spehro Pefhany

Apparently 2ø 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] 2ø motors... may have been {~30hp} turnstile drive and {~5hp} hydraulic pump.

An 1894 quote by CF Scott?creator of the "Scott-Tee" 3ø-2ø 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

X-No-Archive: Yes

Someone here mentioned main entry wires for multi-thousand ampere service uses paralleled wires. If this is ok, why not in smaller scale?

Joe 90 wrote:

Short answer:Because the NEC dose not allow it for wires smaller than 1/0. Longer answer: Because if one wire was damaged, opened up, etc, the entire load would be carried by the other wire, which is greatly over the rating of the other wire and is a fire waiting to happen.

Parallel conductors are always less desirable than a single conductor. The number of potential points of failure are effectively doubled. It is simply a matter of practicality. When single conductors get too big they can't be handled as easily, Conduits have to get larger with wider sweeps, wire bending space increases and cabinets get huge, so they compromise at 1/0 and above. You are also a lot more likely to be under continuous supervision by qualified personnel in a large plant like this.

Nope!

Once the conductor size gets to the point where skin depth is on the order of the radius then parallel conductors will work better than single BIG conductors.

But, of course, you point that the real reason for the NEC approval for parallel conductors above a certain size is for practical rather than theoretical considerations.

With the exception of "single" (known in the trade as "solid") bare 4, 6 & 8 ga copper for grounding electrode conductors there are not many true single conductors above 10 guage. See 310.3 We were considering stranded conductors under a single jacket a single conductor even if it was 750kcmil.

Then use 4 wires in parallel and solder them together at the ends to ensure this doesn't happen.

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