How does the typical mains power connect in the USA anyway?

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On Mon, 25 Nov 2013 15:10:28 -0500, clare wrote:

Everything you said about the "single phase" center tap made perfect sense.
People keep saying the neutral wires is normally bare, but, I must say, mine is insulated.
http://farm4.staticflickr.com/3780/10932993223_cb9139da3c_o.gif
Maybe that's odd, for the USA though, 'cuz everyone is saying that the neutral is normally bare.
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No, they are not.
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On Mon, 25 Nov 2013 19:59:22 -0600, Nightcrawler®

Entering the house (on the PowerCo's side of the meter), it often is bare. There isn't much reason to insulate it since it's tied to ground at both ends (and is out of reach in the rare case of a fault).
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I am aware of this. It is a weight/cost saving move. It is also a fusible link. :-) Just hope the fuse on the pig blows.
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On Tue, 26 Nov 2013 22:39:43 -0600, Nightcrawler®

How is it a fusible link? There can't be more current in the neutral than in either of the hots.
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Um, that was a joke. A pin-hole in one of the hots will slowly erode the messenger cable. A slow blow fusible link?
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On Mon, 25 Nov 2013 21:31:54 +0000 (UTC), Danny D'Amico

of rural Sakatchewan Canada, where single wire earth return IS actually still in limited use) In SWERT there is no "safety ground" and it is not uncommon to get a shock when standing on the "ground" and touching something that is connected to the "ground" some distance away - like a water trough, fed with a steel pipe from a somewhat distant water pump. If the trough is set on rock, or on a wooden base, and an animal is standing in the mud and goes to take a drink, they can recieve a rather nasty shock....
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snipped-for-privacy@snyder.on.ca wrote in

Absolute nonsense. You see bare neutrals all over the place in rural areas of the U.S. with overhead service.
http://www.southwire.com/products/TriplexServiceDrop.htm
Don't you think it's time you stopped assuming that what is true in your [obviously limited] experience is true everywhere?
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I've been kind of following this thread, and I can follow the notion that in a perfectly balanced electrical load the voltage and current sine waves would all cancel out when they met at the neutral wire and so there wouldn't be any current or voltage in either the neutral or ground wires.
But, in a real life situation, suppose I made a point of driving my CRT style TV sets (capacitive loads) and CRT style computer monitors with one power line coming into my house, and at the same time I used the other 120 VAC power line to provide power to all of the electric motors in my house, like the circulating pump on my hot water heating system, the motor in my garage door opener and the compressor motor in my fridge.
Now, according to ELI the ICE man, the current sine waves going through the motors is going to lag behind the applied voltage sine wave, while the current sine waves coming out of the CRT style TV sets and computer monitors is going to precede the applied voltage sine wave. That would mean that the current sine waves returning to the main panel along the white wires would occur at different times, and therefore NOT cancel each other out completely.
Now, I cannot fit it into my head that the voltage sine waves in the neutral wires coming back from those two kinds of loads would cancel each other completely in the neutral buss in the main panel, but not the current sine waves. That would mean that you'd have some NET current sine wave, and therefore current, without any driving voltage.
In order for there to be some NET current sine wave, there HAS TO BE some net voltage sine wave in the white neutral buss in the main panel where all the white wires meet to drive that current.
And I can't see why that net voltage sine wave wouldn't energize the ground cable coming out of the main panel and cause current to flow through that cable and into and out of the Good Earth.
What am I missing here?
--
nestork


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On Tue, 26 Nov 2013 05:55:20 +0100, nestork wrote:

I loved your description. It was an elegantly written logical thought process. I like the way your mind works!
To clarify this important issue, this is what I found: "The power company essentially uses the earth as one of the wires in the power system. The earth is a pretty good conductor and it is huge, so it makes a good return path for electrons."
That was found in an EE class taught by this associate professor: http://www.science.smith.edu/~jcardell/
This is the EE class where that concept is being taught: http://www.science.smith.edu/~jcardell/Courses/EGR220/ EGR 220, Spring 2013, Engineering Circuit Theory
That statement above is part of the curriculum on power generation and distribution in the United States: http://www.science.smith.edu/~jcardell/Courses/EGR220/ElecPwr_HSW.html
So, like you, since the fact the ground is used as the return path for electrons seems to be as clear as day, I wonder why there are vehement arguments (some of which are getting unnecessarily personal) that it's not.
I'm ok with the answer being either way. I don't care who is right and who is wrong (and I'll admit when I'm wrong any time that I am).
But, this one seems clear as the earth revolves around the sun.
But, maybe I'm wrong. Maybe the earth is *not* used as a return path for electrons back to the power company.
Q: Can anyone find a reliable reference that refutes the statement above (taught in EE classes) that the earth is used as a return path for electrons back to the power company?
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On Tue, 26 Nov 2013 05:31:45 +0000 (UTC), Danny D'Amico

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On Tue, 26 Nov 2013 08:22:27 -0500, clare wrote:

Indeed. The return path to the power company's transformers is complex.
I've found a few references that try to explain it (some of which are on google books, so I can never tell if you'll see the same pages that I do).
The math is horrendously complex.
But the summary is simple: "The power company essentially uses the earth as one of the wires in the power system. The earth is a pretty good conductor and it is huge, so it makes a good return path for electrons."
Anyway, I'm moving on to trying to understand *why* and *when* the power companies use the wye versus the delta transformers ...
I'm starting with the *simplified* answer, and then working toward the key details: http://www.phaseconverterinfo.com/phaseconverter_deltawye.htm
"Three-phase power is most commonly provided by the electric utility in a wye configuration. The main advantage to wye power is that the phase-to-neutral voltage is equal on all three legs."
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On Tuesday, November 26, 2013 9:28:16 AM UTC-5, Danny D'Amico wrote:

If you post that same verbage from "How stuff works", one more time, we're all going to throw up.

Hopeless.
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On Tue, 26 Nov 2013 14:28:16 +0000 (UTC), Danny D'Amico

Delta is still used quite a bit in small services where the customer also has a significant line to neutral load and prefers 240 L/L The power company likes it because they can do it with 2 transformers instead of 3. The down side is one of the legs ends up 208v to ground. The other 2 are just like a regular 120/240 because the system is grounded at the center tap of one of the transformers. Look at the transformers and you can tell.
3 p Wye with wye distribution
http://gfretwell.com/electrical/3%20p%20wye-wye.jpg
3 P delta (center tapped)
http://gfretwell.com/electrical/High%20Leg%20Delta%20transormers.jpg
Typically they use a larger transformer on the 120/240 pair to handle the L/N loads
Here is the only example of 240 center tapped delta I have ever seen with 3 transformers (behind the Hogs Breath in Key West)
http://gfretwell.com/electrical/Transformers_at_hogs%20_breath.jpg
The thing that attracted my attention was it still had one larger transformer. If you trace the connections you can see it
There is also a corner grounded delta but you usually only see it in places like sewer lift stations where there is no L/N load at all. The equipment will look exactly like single phase with 2 pole breakers and a white neutral but the voltages are 240 to ground on the ungrounded legs and 240 P to P
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On 11/26/2013 10:57 AM, snipped-for-privacy@aol.com wrote:

You are the king of pictures.
(But that should further confuse Danny. Maybe if he started with the basics...)

Corner grounded delta is also common, I have heard, for center pivot irrigation. Not likely something you have in Florida.
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I am not surprised. It is basically the same operation, a big 3p pump with little else but a starter.
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On 11/26/13 11:55 AM, bud-- wrote:

At least three of the local REAs use the 480v corner ground delta for irrigation here in south central Nebraska. One uses the 480v center tap delta. I haven't seen any circuit breakers used for irrigation. Everyone still uses fuses. Electricians do use breakers for grain bin and building power though. There are a lot more circuits needed for grain handling and buildings. Plus condensation isn't the issue it can be with irrigation.
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Seeing as how we are talking about transformers, and to further confuse Danny... And to bring in 2-phase...
Distribution in a relatively large building may be 480/277V 3-phase. Large motors are 480V 3-phase and lighting is 277V. Scattered around the building are 480/277V to 208/120V transformer (all of this is 3-phase, wye). There are 3 transformers in one assembly.
Relatively small transformers can be made with 2 transformers in one assembly with the transformers in a Scott ( or T) connection. The 2 transformers operate at true 2-phase, 90 degrees out of phase. Long live 2-phase.
The problem with this connection is it screws up the power factor and the current rating of the transformers has to be lowered. The same thing happens with open delta.
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http://preview.tinyurl.com/n8wk3p5
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