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

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On Monday, November 18, 2013 4:52:51 PM UTC-5, snipped-for-privacy@attt.bizz wrote:

Yes you have to snip them because they are irrefutable and show that you;re wrong.
Typical, more name calling when you've lost an argument. Is the IEEE lying too? Here from the peer reviewed IEEE, a paper presented at a conference of power engineers:
http://ieeexplore.ieee.org/xpl/articleDetails.jsp?reload=true&arnumber4520128
"Distribution engineers have treated the standard "singlephase" distributio n transformer connection as single phase because from the primary side of t he transformer these connections are single phase and in the case of standa rd rural distribution single phase line to ground. However, with the advent of detailed circuit modeling we are beginning to see distribution modeling and analysis being accomplished past the transformer to the secondary. Whi ch now brings into focus the reality that standard 120/240 secondary system s are not single phase line to ground systems, instead they are three wire systems with two phases and one ground wires. Further, the standard 120/240 secondary is different from the two phase primary system in that the secon dary phases are separated by 180 degrees instead of three phases separated by 120 degrees. "
Or how about this:
http://www.assocpower.com/index.php?Single-Phase-Power
A split-phase (240/120V) power system is a 3-wire, single-phase, mid-point neutral system, which consists of two 120V "voltage sources"; connected out -of-phase by 180 electrical degrees with a neutral connection between them.
Or this:
http://www.samlexamerica.com/support/documents/WhitePaper-120240VACSingleSp litPhaseandMultiWireBranchCircuits.pdf
"The phase of hot leg 2 (phase B) is in the opposite direction, ie 180 deg apart from the phase of hot leg 1 (phase A)"
"The secondary of the distribution transformer has a grounded center tap and is wound in a manner that supplies two 120V AC phases which are 180 deg out of phase with each other (split phases)"
They even go on to talk about using a oscilloscopet to look at them and say:
"This indicates that the two 120V AC voltages are 180 deg out of phase"
Go ahead, snip those truths too and keep making an ass of yourself.
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Here's what I'm not getting at the moment. What are the connections to tha t transformer? If it is 3 phase leg to neutral on the primary side, then th e center tap should be above neutral on the secondary (house) side, right? Which would mean that house neutral is NOT at ground level. But I'm pretty sure it is.
your confusion is becasue you don't understand how a transformer works. Th e pri and secondary are isolated from each other. The center tap of the se c has NO RELATIONSHIP to the primary. Think of the secondary as seperate f loating power supply not related to the primary. The center tap of the sec ondary is neutral or ground ONLY becasue it gets connected to ground. Sinc e it is connected to ground the two ends become +120 and -120 relative to n eutral.
Mark
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snipped-for-privacy@yahoo.com;3151685 Wrote: > Here's what I'm not getting at the moment. What are the connections to > that transformer? If it is 3 phase leg to neutral on the primary side, > then the center tap should be above neutral on the secondary (house) > side, right? Which would mean that house neutral is NOT at ground level. > But I'm pretty sure it is.

> The pri and secondary are isolated from each other. The center tap of > the sec has NO RELATIONSHIP to the primary. Think of the secondary as > seperate floating power supply not related to the primary. The center > tap of the secondary is neutral or ground ONLY becasue it gets connected > to ground. Since it is connected to ground the two ends become +120 and > -120 relative to neutral.

Mark:
I find the first diagram on this web page that was posted by SRN helpful:
http://tinyurl.com/ly24tjo
It shows the primary side of the distribution transformer connected between the 7200 VAC carried by the single phase wire and ground.
What I can't figure out here, tho, is that if the distribution transformer on the telephone pole is connected to ground, then it's connected via the ground wire that goes down the pole and is wrapped around the base of the telephone pole. So far as I know, that ground wire is not insulated, so that anyone that touches that ground wire would get a 7200 volt shock, which would surely kill them.
So, I think that wiring diagram is mostly correct, but I think there's a problem with the primary side of the transformer connected to ground via the telephone pole's grounding wire.
--
nestork


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On Tuesday, November 19, 2013 12:03:14 PM UTC-5, nestork wrote:

Don't let krw see that. The reference clearly says that with a spit-phase 240v/120v service, there are two phases present and they differ by 180 degrees. He says that just can't be.

Even if it were only connected that way, you would only get a shock if the ground wire were broken and you grabbed the energized end. Otherwise if you grabbed an intact wire, the only voltage present would be whatever there is due to the small resistance of the wire, which would result in a small voltage drop across the wire run. The 7200 volts is across the transformer. The 25 ft of copper wire only drops a few volts, depending on the current flowing in it and the resistance of the wire.
Actually the transformer is typically connected to a primary neutral. The primary neutral is in turn connected to ground much like on the secondary (house) side. It's not necessarily at every transformer, but periodically along the run. Other transformers connected to the same neutral, but from different phases, will balance out and reduce the current flowing in the neutral.

Yes, IMO, they should have shown the primary connected to a neutral, not just ground.
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<snip>

http://www.allaboutcircuits.com/vol_2/chpt_10/1.html

<more snip>
They used to provide a protective cover for the transformer ground. In the old days it was a U-shaped channel milled out of wood.
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On Tuesday, November 19, 2013 12:03:14 PM UTC-5, nestork wrote:
to neutral on the primary side, > then the center tap should be above neutr al on the secondary (house) > side, right? Which would mean that house neut ral is NOT at ground level. > But I'm pretty sure it is. > > your confusion is becasue you don't understand how a transformer works. > The pri and sec ondary are isolated from each other. The center tap of > the sec has NO REL ATIONSHIP to the primary. Think of the secondary as > seperate floating pow er supply not related to the primary. The center > tap of the secondary is neutral or ground ONLY becasue it gets connected > to ground. Since it is c onnected to ground the two ends become +120 and > -120 relative to neutral. > > Mark Mark: I find the first diagram on this web page that was posted b y SRN helpful: http://tinyurl.com/ly24tjo It shows the primary side of the distribution transformer connected between the 7200 VAC carried by the sing le phase wire and ground. What I can't figure out here, tho, is that if the distribution transformer on the telephone pole is connected to ground, the n it's connected via the ground wire that goes down the pole and is wrapped around the base of the telephone pole. So far as I know, that ground wire is not insulated, so that anyone that touches that ground wire would get a 7200 volt shock, which would surely kill them. So, I think that wiring diag ram is mostly correct, but I think there's a problem with the primary side of the transformer connected to ground via the telephone pole's grounding w ire. -- nestork
OK..
in the diagram, the top of the primary is connected to 7200Volts and the bo ttom of the primary is connected to ground. THe voltage on the wire connec ted to ground is close to 0. It doesn't matter that some of the current pa ssing through that wire started out at 7200 Volts. As long as the wire is connected to ground, it is ground. So someone can touch that wire with no problem.
BUT.. if the ground connection to the wire should come loose, then the wire will have a high voltage on it and would be dangerous, becuase it has curr ent in it "that is trying to get to ground" and can't.
That is actually the same danger in the 3 wire dreyer circuit. The ground and neutral share the same wire and if the connection to that wire comes lo ose, the "ground wire" will have dangerous voltage on it.
On the pole transformer, ther bottom side of the primary coil is connected to ground, but the wire you see running down the pole is NOT the ONLY conne ction to ground. All the grounds in the entire distribution system are con nected together so if the ground to one particular pole should come loose, the wire is still probably at ground due to all the other connections. But if I saw a loose ground wire running down a pole, I still would not want t o touch it.
Mark
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Mark:
But, if what you're saying is true, then there is power flowing to ground through the primary coil of every distribution transformer in the USA and Canada 24 hours per day, 7 days per week, 365 days per year.
And, with a voltage of 7200 volts driving that current, it would seem to me there would be a significant current flowing in the 40 or 50 foot cable going down from the transformer to the ground.
Why don't those cables get warm to the touch?
Is it entirely the impedance of the primary coil in the transformer? There is a 24 VAC doorbell transformer in every house in the USA and Canada. 120 Volt power is flowing through the primary coil of those transformers 24/7/365 and yet no one seems to be concerned about that power wastage. And, the only thing that makes sense here is that the impedance of the primary coil is so high that the current flow to ground is actually very small. Ditto for household transformers.
--
nestork


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On Tuesday, November 19, 2013 8:50:23 PM UTC-5, nestork wrote:

All the power isn't flowing in those ground wires. You typically have a neutral that is shared by multiple transformers. Each transformer isn't connected to the same phase, they are connected to phases in a distributed fashion. That means that the current in the neutral is only the unbalanced portion. If you had 3 transformers for 3 groups of houses, each on a seperate primary phase, with equal loads, the neutral current would sum to zero.
And then you have the neutral grounded periodically along it's run, with a heavy, properly sized, ground wire, capable of handling the current through it.

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On Fri, 22 Nov 2013 05:58:03 -0800, snipped-for-privacy@optonline.net wrote:

I'm going to make a stab at *guessing* what A & B are in my main breaker panel.
Is this correct?
http://farm8.staticflickr.com/7294/11045286674_923c991e33_o.png
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On Monday, November 25, 2013 3:07:59 AM UTC-5, Danny D'Amico wrote:

Yes, they alternate vertically.
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On Tue, 19 Nov 2013 18:03:14 +0100, nestork wrote:

Here's a PNG of that diagram, for reference:
http://farm8.staticflickr.com/7292/10955976554_054ba18de1_o.png
In the dryer thread, it was noted that most USA circuit breakers are *not* arrayed in AB-AB-AB format; but in AA-BB-AA-BB format.
I'm not sure what that means though...
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On Friday, November 22, 2013 4:37:03 AM UTC-5, Danny D'Amico wrote:

It's referring to where the two legs/phases show up in the panel. But, I'm not sure what AB means either. You need to define what the perspective is. Just saying AB is meaningless, because it could mean A is on the left, B on the right, or it could mean A is above, B is just below it. In any case, what you have, is the latter. That is what is shown in your diagram. Otherwise you would get zero from a double pole breaker instead of 240V.
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This is correct. My issue with the example provided was that there were an A phase and a B phase shown, inline, left to right. I have yet to see a panel with this layout. Even with three phase panels, the layout is A, B, C. Top to bottom, identical on both sides of the panel. The only deviation that I have seen is when the bus tabs are used for the main breaker input, and this only causes the loss of two connection points in the panel. This is a very common practice in MCC distribution panels. So, 22 circuits... :-)
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I meant to state load center, not distribution panel. Might as well quit before the brain keeps a fartin'.
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Your panel is ABABAB...AB from top to bottom, on both sides of the breaker panel (left/right). The example given in your .png showed AB....AB on the left, and BA....BA on the right. This is a lay-out that makes zero sense and would require some goofy bus work to accomplish. If you look at your breaker mounting points you will notice that every other bus tab, from top to bottom, is the same. So, the top two bus tabs, inline from left to right are phase A. The next row down will be phase B, inline from left to right. A 2-pole breaker will take up two spaces, top to bottom and will give you both an A and a B phase. A 2-pole breaker mounted to its right will pick up the same bus tabs as the first breaker, but, of course, it will be to the right of the first circuit breaker. Just look at the two breakers that currently exist at the top of your panel. They are end to end with their operators (handles) moving in opposite directions to achieve the same action. Yet, the wiring is the same for both breaker, top to bottom. Meaning that if you where to have black and red wires denoting phasing, the black would go on A, and the red would go on B. This is a universal construct in electrical work. Black is always A, Red is always B, and if three phase, blue would be C. A three phase Delta would replace the red with an orange, denoting the fact that the system is Delta, and that the B phase to ground is a high leg and is not 120v and is not to be used for 120v circuits.
Colors are important!
I worked in a 240 Delta panel once that was phase taped for a Wye connection. Black, Red, Blue. I needed to move a single pole breaker down one slot to install a 3 pole breaker. There was a single pole breaker at the top of the panel, on that side, so this put the breaker I had to move down onto the high leg. I did not notice this and since my boss just said hurry up, get it done, and lets get out of here, I did not check the voltage. Well, someone went into the bathroom and the fart fan ran really fast for about 10 seconds before it went up in a puff of smoke and the incandescent lamp was really bright, too. Until it blew up. Never take anything for granted for when you do so, you or someone else might get hurt.
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On Fri, 22 Nov 2013 23:11:08 -0600, Nightcrawler® wrote:

I wish whoever kept posting that PDF would have known that and not posted it then, because that's what we were going on.

Makes sense.

I like that we can *see* that, given there are two hots coming out of the 240V breaker, so, it *must* be phase A & B.
http://farm6.staticflickr.com/5484/10951784553_afa8b636fc_o.gif

This is an interesting observation.

Ah. This is news to me. So, all reds, in the breaker panel, would be B then. But, isn't this red wire on A?
http://farm4.staticflickr.com/3696/10951545765_ec38f77b97_o.gif
Here's a further-out view of that same breaker:
http://farm4.staticflickr.com/3794/10951613376_89cfcb99fb_o.gif
Since the red is on top, isn't that phase A (and not phase B)?
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On Monday, November 25, 2013 2:50:25 AM UTC-5, Danny D'Amico wrote:

Which one you call A and which B is arbitrary. What matters is that you wind up with the phases alternating on the breaker slots, vertically. That way with a double pole breaker, you get 240V. If they didn't alternate, you'd get 0v.
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On Mon, 25 Nov 2013 05:15:29 -0800, snipped-for-privacy@optonline.net wrote:

I'm ok with that.
It was interesting to see the "C" shaped flat metal plates under each of the breakers in my panel.
That shows that my panel is a row of AA, then a row of BB, then a row of AA, and BB, etc.
Thanks to you guys, I can *look* at a panel and tell something about it now. That feels good.
(I hate not knowing stuff.)
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On Mon, 18 Nov 2013 06:48:27 -0800, snipped-for-privacy@optonline.net wrote:

Here are six distribution wires, by the way ... :)
http://farm8.staticflickr.com/7456/10991456846_b2349dd5b6_o.gif
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Danny D'Amico wrote :

Notice each pair of your 6 wires is connected at the insulator so although there are 6 WIRES ther are only 3 THREE conductors
Please before you demonstrate your ignorance and confuse people who admit they dont know, go back to shcool. :-?
--
John G



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