30A wiring advice

Maybe you could explain?

-- Regards, Doug Miller (alphageek-at-milmac-dot-com)

Whereas On Thu, 2 Oct 2003 07:12:21 -0400, "John McGaw" scribbled: , I thus relpy:

I was under the impreddsion you wern't sure if CH was indeed Switzerland, or some poor country that sold their TLD to companies for anonymous users.

What is being overlooked here is that the non-USA way of thinking is not nearly as do it yourself (DIY) as we have here in the USA. Much more wiring/painting/remodeling, etc is hired out than we are used to here in the USA. So the availability of things like heavier gauge wire is really limited. I would suggest looking for a commercial demolition site and scrounging the wire, if it is not against the local law to scrounge.

H. R. (Bob) Hofmann

Which essentially states 120/240V system is single phase, not multiple.

Actually it is trivially easy to generate 90 degree two (or four as you call it) phase from a 3 phase supply. It only takes 2 transformers to do so (look up "Scott-T configuration"). Actually with a proper configuration you can generate any polyphase system from any other polyphase system with only tapped transformers, EXCEPT you can't generate polyphase from single phase. You can't generate it from center-tapped single phase/"two phase", either, but you CAN generate 3 phase from 90 degree 2 phase. I could run my 7 phase widget (if there was such a thing as a 7 phase widget) from the 3 phase supply if I had to, as long as I could get the proper transformers (and figure out what transformers I needed!)

You shouldn't be looking at the phase of the voltages, but the phases of the _power_ on each line (to a resistive load). On a 120V/240V American system the power is always in phase no matter how you wire the load.

Could this mean that status inconsistency is more rampant here in the US than it is in Europe? After all, in Switzerland, it might be that if my income is higher than an electrician's income, I would probably hire somebody to do my electrical work because it wouldn't be worth my time to do it myself. And if my income is lower than an electrician's income, I probably wouldn't be able to do what an electrician can do - in which case I would probably hire this work out anyway. In the US, on the other hand, it's not inconceivable that there are many more people who can do what an electrician can do but who don't make as much money as an electrician. In such an environment, you would probably find many more do-it-yourselfers.

Just a thought. :-)

Robert

JRS: In article , seen in news:sci.e ngr.electrical.compliance, John Woodgate 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.

, 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.

It isn't really that simple. When you hire an electrician you are not only paying his salary, you are paying his taxes, license fees, insurance, inventory carrying charges for what's on his truck and all the fees related to his truck along with whatever support staff he needs to keep him in the field. An electrician making $15 an hour probably bills house calls at $80-90 an hour with a one hour minimum and travel time. That's in a non-union state like Florida. Certainly a lot of people still choose to pay for doing things but the rise of places like Home Depot demonstrates that plenty don't.

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

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.

I read in sci.engr.electrical.compliance that Dr John Stockton wrote (in ) about '30A wiring advice - a complication?', on Thu, 2 Oct 2003:

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.

Hmm, BS 7671 allows a single overcurrent protective device to be used with parallel conductors provided that:

- the sizing and layout is such as to ensure equal current sharing, and

- there are no branches taken off one of the cables (ring final circuits are exempted from this), and

- a fault anywhere on one of the circuit cables will operate the device without exceeding the relevant conductor temperature limit (adiabatic compliance).

Multiple devices are only required if the above can't be complied with. See regulations 473-01-06 thro' 473-01-08, 473-02-05 and

But as you say, the design calculations required are well beyond the capability of the average electrician, so it doesn't happen very often.

JRS: In article , seen in news:sci.e ngr.electrical.compliance, John Woodgate posted at Fri, 3 Oct 2003 06:35:08 :-

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 ...

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

Whereas On Fri, 3 Oct 2003 06:35:08 +0100, John Woodgate scribbled: , 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.

Whereas On Thu, 2 Oct 2003 18:36:42 -0700, "s" scribbled: , I thus relpy:

You could do that with two genuine 2 phase supplies.

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

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

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.