30A wiring advice

Page 2 of 5  


Or that I am thinking things through very logically. The confusion stems from page 23, of Wiring Simplified 39th edition based on NEC 1999 by Richter and Schwan. It implies that supplies in USA are in single phase whereas I would have expected a 180deg phase differential which has indeed been confirmed by a few posters.
Also just to underline, when dealing with any such DIY projects I do get a qualified electrician in to validate the work before switching on. As far as I am aware I have not broken any Swiss regs.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I read in sci.engr.electrical.compliance that Joe 90
about '30A wiring advice - a complication?', on Wed, 1 Oct 2003:

Yes, well, you and me both. I have had scorn and derision heaped by US citizens for describing their system as 'two-phase'. But it IS! (;-)
--
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
Interested in professional sound reinforcement and distribution? Then go to
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
it isnt two phase!i know that and im a british sparky living and working in the uk!!it IS single phase,fed from either end of a centre tapped transfomer,in exactly the same way as our 110 volt transformers we use for site tools.120v----0v(neutral)----120v.240v end to end,120 end to middle.if you need to know how this works,think of a sine wave with the centre line being the centre tap on our transformer!!(rant over). :-P

http://www.jmwa.demon.co.uk
to
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wiring advice - a complication?', on Wed, 1 Oct 2003:

Well, I'm a Chartered Electrical Engineer, living and working in UK, and although your detailed explanation is correct, that IS the description of a two-phase system.
Just as the phase angles between the conductors of a 3-phase system are 120 degrees, so that the three angles add to 360 degrees, the angles between the phases of a 2-phase system are 180 degrees, adding up to 360 degrees.
--
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
Interested in professional sound reinforcement and distribution? Then go to
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
im sorry to disagree but i dont consider this to be a true two phase system,as only one phase is entering the transformer,one leaving.the centre tap being there for safety/alternate voltage.if this were a true two phase,then it could be fed straight into a squirrel cage motor without the need of a starting capacitor to phase shift the feild,or am i missing something quite fundamental here??
about '30A

http://www.jmwa.demon.co.uk
to
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wiring advice - a complication?', on Wed, 1 Oct 2003:

If you look at it like that, you get the confusion that troubled the OP. You have chosen the explanation of the centre-tap to 'prove' your assertion. But one 120 V supply behaves exactly as a single-phase supply, and so does the other. When you look at the two together, the important phase-difference comes into consideration. Your explanation 'hides' the phase-difference.

Yes, you are missing something. A two-phase system does not create a rotating magnetic field, as a 3- or higher- phase system can do. So the motor won't start. The starting capacitor and the second winding DO create a rotating field.
A 'two-phase' system with 90 degrees between the legs (which is really half a 4-phase system - the angles must add up to 360 degrees) would create a rotating field, but it is not easy to derive such a supply from the public electricity system.
--
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
Interested in professional sound reinforcement and distribution? Then go to
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
posted at Thu, 2 Oct 2003 08:28:29 :-

If you count 3-phase as public : It is I believe delivered in the UK as star, with a neutral near ground.
Connect a 1:1 transformer to one leg, neutral to live wire. Connect a Root3:1 transformer between the other two live wires.
ISTM that one then gets two outputs in quadrature, of equal magnitude.
Admittedly it is impractical to use an integer multiple of Root3 turns, but 97:56 is within 1 in 10^4.
<URL:http://www.merlyn.demon.co.uk/js-demos.htm#App , enter Math.sqrt(3)
Note, though, that the three supply phases are not equally loaded, and I've not worked out whether there is neutral current. Loading could be made to balance with an auxiliary two-input transformer, driven from the second two legs, and connected to buck/boost the output of the first transformer, I think.
Untested.
--
John Stockton, Surrey, UK. ?@merlyn.demon.co.uk Turnpike v4.00 IE 4
<URL:http://jibbering.com/faq/ Jim Ley's FAQ for news:comp.lang.javascript
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I read in sci.engr.electrical.compliance that Dr John Stockton

Well, the distribution itself isn't really either star or delta, but no neutral comes with it. The neutral is earthed at the sub-station.

So you would need this transformer to have three secondaries in star, with only one used.

I'm not sure whether you could incorporate such a secondary on the same three-phase core as the first transformer, by winding it round two 'legs'. Possibly. Many such arcane transformer configurations exist.

Ingenious, though. Simple, for sufficiently difficult values of simple.
--
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
Interested in professional sound reinforcement and distribution? Then go to
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I think you did not read as much into "delivered" as I tried to write into it. I meant it as four wires, one being almost safe to touch.
ISTM that any 3-phase transformer must contain (at least) three distinct pieces of iron capable of being wound. As ISTM you suggest, with a winding on one, and windings on the other two in series, one can get the desired quadrature-phase output.
Sometimes I wonder what could be done with a winding around each edge of a skeleton iron tetrahedron, using one face for input and the other edges for output, or vice-versa, or ...
--
John Stockton, Surrey, UK. ?@merlyn.demon.co.uk / ??. snipped-for-privacy@physics.org
Web <URL:http://www.merlyn.demon.co.uk/ - FAQish topics, acronyms, & links.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
seen in news:sci.e

That's an interesting thought. Wonder which way the flux would align in it.
I have seen three-phase transformers that were three vertical irons tied with cross bars at top and bottom. Kind of like 'III'. The primary and secondary were wound on top of each other, one phase per leg. Took up less space than three conventional single phase units. It was were 'space and weight considerations' were more important than money (i.e. military).
daestrom
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Whereas On Fri, 3 Oct 2003 06:35:08 +0100, John Woodgate
, I thus relpy:

FWIW, the UK MV distribution system is 11KV delta, and is transformed to a 230/380V Wye, with one phase per home.
The US usually uses a Wye system for the MV, with one phase (hence single-phase) Hot-Neutral, with a center tapped 240V transformer, the center tap being gorund/neutral.
--
Gary J. Tait . Email is at yahoo.com ; ID:classicsat

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
does four phase system exist in the real world?not very efficient i would'nt have thought,as phases 90 degs apart would have a much smaller potential than a similar system at 120 degs apart,otherwise a four phase system would be used for sheer economy,would it not?
about '30A

http://www.jmwa.demon.co.uk
to
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 2 Oct 2003 18:36:42 -0700, the renowned "s"

There exist 5-phase synchronous motors (steppers). They run more smoothly than the more common 2-phase type. Of course the power for them does not come directly out of a plug in the wall.
Best regards, Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
snipped-for-privacy@interlog.com Info for manufacturers: http://www.trexon.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
scribbled: , I thus relpy:

You could do that with two genuine 2 phase supplies.

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

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I guess it depends on how you 'count' four phases. Obviously you could call it 'two phases' with center-taps tied together I suppose. But you're right, three phase on a watt/wire basis is more economical. Do the math assuming a fixed current capacity and you'll find three phase is the most economical on a watt/wire basis. Five, seven, nine, eleven, any higher number of phases do not do as well as three. Kind of a geometry/math thingy.
IMHO, anytime one phase is exactly 180 out from another, I don't count that as a separate 'phase'. So a 'four phase' system is really just a two phase system with some center-taps. Kind of like residential supply in US (the so-called Edison connection). Whole flame wars have gone on for days over whether to call that a two-phase system, or just a single phase system with center-tap. FWIW, if one wire is exactly 180 out from another wire, isn't that just like the two wires of a single phase AC supply? Well, don't want to start another war over that, but just pointing out there are differences of opinion.
There have been two phase systems where the two phases are 90 apart. They can produce a rotating field for self-starting machinery. Conventionally, this would take four wires to distribute. But an obvious economy is to tie one leg of each phase together so you only need three wires. This requires a larger conductor for the common conductor and is 'unbalanced' with respect to ground. Causes some problems with telephone service and the like.
daestrom
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
John Woodgate wrote:

You're right; it's a single-phase system with a center tap.

You're right. There were two-phase power systems before there were three-phase systems, and they are still used for a few special purposes.

Yes it does.

No, it's a two-phase three-wire system. A four-phase system has conductors with phase angles that differ by 45 degrees. More explanation below.

It's trivial, using a standard device called a Scott-connected transformer. It consists of two transformers, one connected between phases A and B, and the other connected between the center tap of the first one and phase C. If you choose the ratios of the two transformers correctly, the other windings of the two transformers are 90 degrees out of phase, giving you two-phase power. How you make the connections on the two-phase side determines whether you're dealing with two-phase three-wire, two-phase four-wire, or two-phase five-wire. Being a transformer, this can pass power either from the three-phase system to the two-phase system, or vice versa.
The US standard center-tapped single-phase system is just that; single phase. Three-phase systems can have either three or four wires, depending on whether the neutral is carried along with the phase conductors to allow phase-neutral loads to be connected.
Two-phase systems are more complicated. It can be done with three wires; call them X, Y, and Z, with VXZ leading VYZ by 90 degrees. If VXZ=VYZ=1, then VXY=1.414. With this system, Z is normally grounded and called the "neutral". Two-phase four-wire can be done, too, with no neutral. Calling the wires W, X, Y, and Z, VWY leads VXZ by 90 degrees. If VWX=VXY=VYZ=VZW=1, then VWY=VXZ=1.414. The phase angle between any two adjacent wires is 90 degrees. To make it more complicated, you can do two-phase five-wire, which is just like two-phase four-wire with the addition of the neutral.
AIUI, the original Niagara Falls system was two-phase. The beauty of a three-phase system is that the voltage between any two wires other than the neutral is the same.
73, JohnW
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I read in sci.engr.electrical.compliance that John Wilson
s.asp.att.net>) about '30A wiring advice - a complication?', on Sat, 4 Oct 2003:

You've just chosen definitions that suit your denials.

That is TRIVIAL?
--
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
Interested in professional sound reinforcement and distribution? Then go to
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
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.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.