Talk:Alternating current

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Alternating Current does NOT reverse direction[edit]

The current in a 110 volt line pulses into the neutral line.
The current in the 220 and higher 3 phase lines pulses from multiple lead lines into the neutral line.
All the current travels from the lead line into the neutral line.
To prove this DIODES are used to convert AC into DC.

The current cannot travel from the neutral line into the lead line.

— Preceding unsigned comment added by 108.89.36.16 (talk) 01:02, 27 January 2014 (UTC)

This article is written ONLY for experts[edit]

Wikipedia is an encylopedia. This article is written for people who already know what Alternating Current is and how it is generated. The main article should be simpler and should explain to a common lay person, how alternating current is generated and functions. Advanced discussions should follow or be spun off to another article. And, no I can't be the one to fix it, I'm not qualified to explain the concept, I came to this article to firm up my own understanding. Gdewar (talk) 21:21, 12 April 2008 (UTC)

OK, but some more specific comments would be very helpful; all the people who've been editing to this point seem to think they've explained the subject clearly and if we *haven't* then your specific criticism will be valuable. What,specifically, is wrong? Start with the introduction. When do you start throwing your hands up in the air? C'mon, help us out. --Wtshymanski (talk) 23:31, 16 April 2008 (UTC)

I agree with Gdewar. The whole thing is rather uninformative, but I got really rankled when I came to

For three-phase at utilization voltages a four-wire system is often used. When stepping down three-phase, a transformer with a Delta primary and a Star secondary is often used so there is no need for a neutral on the supply side.

What I came to this article hoping to find out was: how the electrons move in the wire, what's happening at the power station to make them do that, something about hot and neutral, and what's the deal with the two different legs coming into my circuit box. And maybe something about how that back-and-forth electron motion is used to make appliances go. A good starting point for explanation may be to assume knowledge of DC, since that's simpler and easily understood by analogy to plumbing. The distinction between hot-and-neutral vs. negative-and-positive might also be worth a mention. Brock (talk) 19:32, 19 November 2008 (UTC)

I'm not sure if this belongs here, but I know it isn't supposed to be part of the main article now. This is the simplest explanation of Three Phase Alternating Current I can come up with for you...

"The dynamos used to generate North American alternating current are designed to switch polarity 60 times a second, so they build a maximum voltage charge and drop it and then reverse the charge to a maximum negative voltage and drop it and so on, 60 times a second. This creates a high voltage current in the transmission line which reverses direction 60 times a second, saving the transmission line from amperage loads over long distances (electrons travelling in one direction the length of the transmission line will be found in Direct Current only, and they heat the wire easily) and result in high voltage without overheating the transmission line. Since there are down times, when the voltage drops and reverses polarity, it is more efficient to run three dynamos out of phase, and so transmit 180 voltage cycles a second, each of the three lines providing a voltage peak in sequence 60 times a second. Depending on how much power the customer requires, these 3 power lines are available, using transformers to lower the supplied voltage down to the minimum typical household voltage of 110 volts per line. Only two of those lines are delivered to the typical household, since being out of sequence the voltage differential between the positive and negative phases of the two 110 volt lines used to power your clothes dryer and stove will add up to a 220 volt differential for the heavy motors and resistors of the dryer and stove, which is why those 220 volt appliances are served by power from both sides of your circuit breaker panel (each side being connected to only one of the incoming 110 volt phase lines), while the rest of your appliances and lights will be served by only one line providing a single 110 volt cycle. The extra wire going to your appliances is the return to ground wire, which returns to your circuit breaker panel containing the voltage grounding line for the power lines in from the street (without grounding there is no voltage differential available to generate electron flow). This ground wire inside the circuit breaker panel is not the same thing as the ground wire in an appliance. The ground wire in an appliance, which you attach to a ground connection of your own choosing, such as the already wired-to-ground junction box in your wall, will simply divert stray electron flow away from your own body if the appliance short circuits and starts delivering stray electricity to the shell of the appliance, which you might touch." —Preceding unsigned comment added by 75.157.220.85 (talk) 19:48, 22 November 2008 (UTC)

I understand your need for a simple explanation, but quite a lot of what you have written above is simply not true (though some is). I will try to insert a brief paragraph containing just the true bits, so that we don't upset the experts. One difficulty is that the numbers you quote are not true for my country, and this is an international encyclopaedia. Dbfirs 20:25, 22 November 2008 (UTC)
(later) I'm struggling to improve on the introduction. I'm not sure that even experts fully understand the quantum mechanics of electron flow. The plumbing analogy is an over-simplification, even for DC. It is good for a children's encyclopedia, but would not be appropriate in this article. Perhaps we should have a new article: a simple explanation of electricity? Dbfirs 22:55, 22 November 2008 (UTC)

DC to ground?[edit]

I was going to put that unlike DC, AC does not need to return to its source, as it can flow to ground. However, I may be wrong on two counts... Can DC flow to ground as AC can? And also, am I wrong about AC somehow? I think I'm confused... —Preceding unsigned comment added by ReignMan (talkcontribs) 11:01, 1 December 2007

I wouldn't add anything like tis to an article unless I was quite confident in the matter. If you're confused, perhaps you should not edit the article until you've read and understood some good references on the subject. --Wtshymanski (talk) 23:57, 21 December 2007 (UTC)

The AC or DC can flow to ground, if you connect one terminal of a DC supply to ground then you can supply a load via the other terminal of the DC source and return it to ground. The reason AC tpically does this is that "ground" is established at the generation plant and at the customer premises.

Remember the electrons don;t care if they always go the same way or if every so often they reverse direction, so AC and DC behave the exact same way in a lot a respects, like when discussing grounds.

This article also states that the since wave is the most efficient form of energy transfer - this is not the "real" reason AC is sinewave. Sinvewaves are what you get when you have a rotating magnetic field (e.g. in an alternator) - it is quite hard to generate a triangle or sawtooth or square wave mechanically as it requires rapid cahnges in direction. Technically this means the sine is more efficient but it's a bad way to state it. —Preceding unsigned comment added by 60.234.222.212 (talk) 06:52, 14 October 2008 (UTC)

The sine wave is the most efficient for transforming voltages with least loss. That's why it is the most efficient for energy transfer. Dbfirs 20:30, 22 November 2008 (UTC)

Mathematics of AC Voltages[edit]

Why is this discussion done in terms of voltage? I realize that ac voltage often accompanies ac current, but seeing as how this is an article about ac current it seems better to just stick to ac current. The math won't be any different, so I just don't see the reason to switch to voltage for calculations. —Preceding unsigned comment added by 146.115.120.149 (talk) 20:18, 20 September 2006

Good question. The example provided in the section uses voltages because that is what can be measured from the wall's outlet. The amount of current depends on the load resistance, but the RMS voltage is more or less a constant (the instantaneous is obviously oscillatory). Mr. PIM (talk) 23:29, 21 September 2008 (UTC)

Does anybody really know what times sign it is?[edit]

Just wondering if anyone else finds it confusing that the multiplication sign is an 'X', the symbol for cross product. I realize that this or a dot are often used, but with the inclusion of the sine function in the equation already it may be misleading. --Bmalicoat 23:47, 26 October 2005 (UTC)

The problem, of course, is that the "x" is the Wiki-generated symbol from the "times" markup (shown below). As long as that's the case, I think it should stand as currently written. You could, of course, start lobbying the Wiki software guys for a change (that would affect every usage of "times").
:<math>v(t)=A \times\sin(\omega t),</math>
Atlant 12:07, 27 October 2005 (UTC)
Ahh, I didn't realize that, thanks.
Bmalicoat 03:12, 28 October 2005 (UTC)

"Primitive" induction coils?[edit]

The wording "His design was a primitive precursor of the modern transformer, called an induction coil" is not very NPOV.

I'd like to see some pictures of AC in action words can't describe it well enough. --Cyberman 02:30, 10 Feb 2005 (UTC)

I think this page is nice. Congratulations to those who've been working on it. I nominated it for featured articles. A picture would be nice, though. Power cables, transformers or something. Washington Irving | Talk 23:21, 25 Mar 2004 (UTC)


I could write a part about transforming DC->AC through a solenoid- condensator circuit and a triode. Anyone think this is useful and/or fitting here?
- Xorx77 17:09, 28 Mar 2004 (UTC)

That would be good, but perhaps it would be more appropriate in the HVDC article under "Rectifying and Inverting". You could add a link from this article to that one. -- Heron 17:16, 28 Mar 2004 (UTC)

I changed the usual Teslaphile stuff to give due credit to some of the other critical workers in the field. Look guys, I know you venerate the guy, but the reality is that his contribution to the field, although undoubtedly important, was just one aspect of many advances in electrical engineering at the time. In particular, describing him as the father or inventor of AC makes a good book blurb but is totally unsupportable. Among the critical parts of the infrastructure he didn't invent were: transformers, the AC distribution system, AC generators, or meters. His major practical contribution was AC motors - and the first one he ever built that actually worked, was under contract to Westinghouse. Securiger 13:18, 21 Jun 2004 (UTC)


Actually the Tesla coil is an 'air core' power transformer: http://en.wikipedia.org/wiki/Tesla_coil. The historical sections of this article are a POV mess and require serious re-writing. Counterinduction. 09.33, 15/4/2014 (GMT)


— Preceding unsigned comment added by 129.234.252.66 (talk) 08:34, 15 April 2014 (UTC)

I updated the sections on power and 3 phase systems, which are hopefully a bit clearer now. Also the section on earths and neutrals which had become a little muddled. The earth is not the same as a neutral. A neutral is used to form a complete circuit in a healthy system, an earth is used to provide a specified path for current during a fault. —Preceding unsigned comment added by 62.172.213.132 (talk) 15:32, 23 September 2004

Perfect sine wave?[edit]

Did the guy who wrote this ever actually stick the probes of an oscilloscope into the wall outlet? —Preceding unsigned comment added by Rsduhamel (talkcontribs) 21:21, 27 December 2004

Where in this article did they talk about a perfect sine wave????? —The preceding unsigned comment was added by 214.3.140.16 (talkcontribs).

Focus[edit]

The article currently has a lot of stuff that is covered in other articles; three phase, grounding, etc. I think the discussion here could be compacted since details are only a mouse-click away. I also cleared up some leading spaces in the talk page - not everyone is signing contributions - use the button for signatures in the editor or else manually put --~~~~ at the end of your comments. --Wtshymanski 17:26, 1 Jun 2005 (UTC)

== I thought the "links" part of the article were to link one article in Wiki to another relavent article. And I appology for being picky, I think that the pictures in the Transformer article are informative to inquisitive readers trying to understand the current technology etc of AC.WFPM18:58, 21 October 2008 (UTC)

Merging everything AC into one article[edit]

I consider the concepts of electrical current/voltage, resistance/reactance and power to be sufficiently different that they should not be merged, otherwise the combined article will become too long and very difficult to organize clearly. I note that there is inadequate discussion in these articles of non-sinusoidal waveforms, particularly of the substantial 3rd and 5th harmonics generated by the non-linearity of standard power transformers - that would make a combined article even longer. Then there are the square and 2-step waveforms of DC-AC power converters. I recommend keeping these three separate but consistent, with appropriate cross links. As a retired electrical engineer, I could try to start this process, but would do so only when agreement is reached on separation. JohnSankey 15:31, 5 October 2005 (UTC)

So much for an offer :-( JohnSankey 22:59, 5 October 2005 (UTC)

Can we remove some of the merge templates then?--John 23:45, 16 October 2005 (UTC)

== I didn't know Engineers ever retired. I thought they just grew old, and "faded away" like Mcarthur. But Engineering is "applied science" and in Wikipedia you have to not have original ideas, but to explain everything in historical and physical and even mathematical concept terms that you and I know that weren't even discussed when you took electrical engineering. So that's the way it is, and good luck. WFPMWFPM (talk) 19:09, 21 October 2008 (UTC)

Nomenclature[edit]

Just to note that "mains power" is a British term. I have never heard it used in North America. JohnSankey 22:59, 5 October 2005 (UTC)

It's used at least occasionally in North America. Especially as compared to (say) "battery power".
Atlant 01:03, 10 October 2005 (UTC)

Real Power / Apparent Power[edit]

Why do these articles simply redirect to this article, when this article makes no mention of them? —Preceding unsigned comment added by 62.56.57.235 (talk) 10:45, 17 October 2005

Problematic entry from the ground-up[edit]

I am sorry if I sound negative, but this article/entry (Alternating current) is un-organized, and even though it's extraordinarely short for such an important and vast subject, it feels too long to read.

The consequences of the bad architecture of the entry, is that even contributors have trouble striking the right balance when trying to add relevant information. For example, Nikola Tesla is under-represented, even though he has almost single-handidly produced virtually all the elements of the puzzle necessary for the AC power system (I won't spend time documenting this point, if anyone thinks it's open to dispute, I'm willing). I don't blame it on anyone's agenda, but simply, on the fact that the article is discouraging of contribution. I have tried, anonymously, to correct few of the more evident errors, and am preparing to beef up the body on Steinmetz and Tesla. Still, every time I think of this wikipedia entry, I feel pain in my stomach, so I keep putting off the big work for another day. Old-fool 17:56, 21 October 2005 (UTC)

One way to handle this dilemma is to create an entirely new version of the article. You can initially create it in something like "Alternating Current/new_version", tweak it until it's as you want it, and then open it up for review and collaborative editing. When the article is "fully baked" we can replace the existing article with the new article.
There is definitely a life-cycle to many Wiki articles:
  1. They're initially created terse
  2. Over time, they "accrete" aditional information, often in a somewhat-jumbled way
  3. At some point, somebody takes the initiative and resturctures the whole thing to make all the accreted info flow as a coherent narrative.
That somebody sounds like you! Time for you to be bold!
Atlant 12:17, 27 October 2005 (UTC)

Power equation problem[edit]

I don't know what you mean by power lost = I^2 * R. This is supposed to be the equation for power transmitted, and since V=I*R, power = V*I also. Therefore, I don't see why the power equation explains why current affects power lost and not voltage. Can someone clarify this please? —Preceding unsigned comment added by 24.184.127.141 (talk) 03:47, 3 November 2005

It depends on which R you are referring to. Power lost is I^2 * R(of the conductor). Power delivered is I^2 * R(of the load). pstudier 03:55, 3 November 2005 (UTC)
I do see a problem with formulas however. P=I^2R and P=IV of course, but coupled with introduction of "This implies that in the same wire, if the current is doubled, the power loss will be four times greater", to some readers this might suggest that if the voltage is doubled, the power loss will NOT be four times greater, which is certainly not the case because P=V^2/R too. Something should be done about this, but I am not sure what. Nikola 09:33, 4 November 2005 (UTC)
You have to be careful, when you are using P=V^2/R, to specify what V you are referring to. Your statement above suggests that you are talking about the voltage drop across the wire. Doubling this would indeed cause a quadrupling of the power loss. However, the V usually referred to in this context is the transmission voltage. Doubling this causes a quartering, not a quadrupling, of the power loss. I'm reluctant to explain this in the article because it would just add confusion where there is presently simplicity. However, I'm open to ideas. --Heron 17:09, 5 November 2005 (UTC)

I think you should explain it since the present simplicity is deceptive and also confusing due to the question of why I should think about I^2 * R instead of V^2/R. —Preceding unsigned comment added by Jcline1 (talkcontribs) 13:39, 26 November 2007 (UTC)

The V in your V^2/R is measured between the ends of one wire - perhaps about one volt, not the supply voltage, but the I is (almost) the same in both the load and the transmitting wire. Doubling the supply voltage will actually reduce the V across the wire by half (approx), because it means that I (the current) can be halved, and V=IR across the wire. Does this help? (I need to draw pictures to make it clearer) Dbfirs 23:07, 22 November 2008 (UTC)

What is AC and DC and what do they do?[edit]

Note: The section heading was added by 156.63.21.11 on 14:35, 28 November 2005 without any content. The comment below is therefore a response to the question posed by this anonymous user in the section heading. Mr. PIM (talk) 16:53, 17 September 2008 (UTC)

I would suggest that you read Wikipedia articles on alternating current and direct current. Nikola 22:54, 28 November 2005 (UTC)

Needs a complete rewrite[edit]

This is a shockingly sparse and badly organised article considering the importance of AC power in the world. —Preceding unsigned comment added by 148.197.54.206 (talk) 15:12, 1 December 2005

Volt-amp[edit]

Volt-amp redirects to this article, but I don't see any mention of it here. In particular, I'd like to know how volt-amps are related to watts. (I thought were the same, but then why is a UPS I'm looking at rated at "500VA" but "300W"?) - dcljr (talk) 04:50, 16 January 2006 (UTC)

i've just changed the redirect to point to AC power. enjoy ;) Plugwash 04:51, 16 January 2006 (UTC)

other parts of the world?[edit]

What other parts of the world? I assume other than the U.S.A. If you take a look at the frequencies used you will notice that 50 hertz is the most commonly used frequecy , with a few (but major) exceptions (mainly North America). It's a minor issue of how you put it , since I don't think all users of wikipedia regard this from the point of view of an american as we can't be all americans :)) —Preceding unsigned comment added by 82.76.35.22 (talk) 07:36, 31 January 2006

To a degree a reasonable point, but modern electrical systems was first developed in the US and then introduced in Europe, so I think the writer is unwittingly formulating it from a historical point of view. More importantly, Wiki shouldn't claim "general acceptance" (opinion) unless it really is so. As best as I can tell from some surfing and reading, the details of the 50-vs-60 HZ developments in the US vs Germany is to a large degree veiled in the mists of history around the previous turn of the century. And the "adapt to metric" theory for 50 Hz appears to be more of a postrationalization (as is the similar claim that 60 Hz makes it easy to have a synchronized clock showing the correct time, which is contradicted by the fact that the patent for such a clock post-dates the 60 Hz decision by decades). What is known is that 50 Hz was decided on by AEG in Germany, which drove the development of electrical power in Europe, and 60 Hz was decided on by Tesla and the Westinghouse team (Stillwell, Shallenberger, Schmid, and Scott). As far as I can tell, that is what is *known*, the rest is theory. I'll update accordingly.--Psm 20:23, 1 August 2006 (UTC)

History of 60 Hz vs 50 Hz[edit]

See my comment above. I'm deleting the following passage and replacing it. Included here in case someone wants to rollback or merge. --Psm 20:27, 1 August 2006 (UTC)

It is generally accepted that [[Nikola Tesla]] chose 60 [[hertz]] as the lowest frequency that would not cause street lighting to flicker visibly. The origin of the 50 hertz frequency used in other parts of the world is open to debate but seems likely to be a rounding off of 60 Hz to the 1-2-5-10 structure, called a set of [[preferred number]]s, popular with metric standards.

60Hz may also have been chosen as it would make for more convinent gearing ratios in electric clocks. A synchronus motor runing on 60Hz rotates at 3600rpm (or a submultiple therof) 3600 rpm through a 60:1 gear ratio is 60rpm (i.e. 1 rev/sec) with succesive 60:1 gear ratios giving 1 rev/min (for the second hand) and 1 rev/hour (for the minute hand) 87.113.7.148 17:48, 12 August 2006 (UTC)

That is just an issue of selecting the right gear ratios. For 50Hz a motor rotating at 3000 rpm through a 50:1 gear ratio is also 60rpm... -- RTC 21:08, 19 August 2006 (UTC)

first sentences are totally wrong...[edit]

An alternating current (AC) is an electrical current where the magnitude and direction of the current varies cyclically, as opposed to direct current, where the direction of the current stays constant. seems wrong.

The only difference between AC and DC is that AC alternate between positive and negative values as DC always stay positive...You can have a perfect sine wave which stay on positive values as a DC current. So the form of the wave as nothing to do with DC or AC. You can also have pulsed waves that can be AC. Magnitude have nothing to do here... —Preceding unsigned comment added by 65.92.142.247 (talk) 22:48, 10 February 2006

I think the author of the statement "You can have a perfect sine wave which stay (sic) on positive values..." wasn't thinking clearly. What must have been meant is that one can have a current that is a perfect sine wave (which, by definition, has positive and negative values) superimposed on a direct (constant) current. A time varying current that is always positive or always negative is not, strictly speaking, DC. It is easy to show that such a time varying current is composed of a direct (constant) current plus one or more alternating currents. For example, the current defined by the following:
i(t) = 1 + sin(2 \pi 60 t)\,
does not change direction but does vary in magnitude. Is it a DC or an AC? The answer is that it is the sum of both. Alfred Centauri 14:24, 9 March 2006 (UTC)


When you are mixing two currents it's sure you can't tell at this moment whether its DC or AC because its both but usually the DC will be use to transport AC and then be divided again by a coil and/or capacitors. The result will be a positive sine-wave and a alternating sine-wave. —Preceding unsigned comment added by 65.93.158.199 (talk) 23:28, 22 March 2006

I'm not sure that we've got to the bottom of this definition yet. There doesn't seem to be a consensus of the meaning of "AC". Here are some examples of the various meanings:
  • Chambers Dictionary of Science & Technology says that (i) it alternates in direction, (ii) it has a constant period of alternation and (iii) the normal waveform is a sinusoid.
  • McGraw Hill Illustrated Dictionary of Electronics gives alternation of polarity as the only criterion, but implies with the use of the word "frequency" that the period should be constant. It does not mention a sinusoid.
  • Horowitz & Hill's The Art of Electronics doesn't attempt a definition, but says that DC signals don't change in time and AC signals do.
I think we should say "AC is any current that repeatedly reverses direction so that its long-term average is zero. Unless the shape of the waveform is specified, it is usually assumed to be a sine wave." --Heron 09:59, 23 March 2006 (UTC)
In generating and transmitting AC electric power you dont mention that the generated VI value is not exactly the absolute VI value but is the "in phase" VI value. And that in AC power it is possible for inductive and/or capacity loads it is possible for a loss in power generating capacity due to the generating voltage getting "out of phase" with the load circuit RLC impedence value. WFPMWFPM (talk) 11:34, 20 October 2008 (UTC)

Can someone more in the history section?[edit]

I forgot most of what i know of AC's history, but im pretty sure Edison hated it... I don't really remember, so I came here. I am dissappointed to find that this info isn't here, so I'll have to look elsewhere for now! Maybe I'll do some research and write it myself if I have time. —Preceding unsigned comment added by 74.130.112.57 (talk) 01:42, 29 July 2006

What you're looking for is probably under War of Currents, but there may be room for some more info in this article. --Heron 13:56, 29 July 2006 (UTC)

Missing sections[edit]

I think this article needs a section on how the alternating current is generated and one on how direct current can be transformed into alternating current. —The preceding unsigned comment was added by 193.226.140.133 (talkcontribs) .

This sounds like the perfect opportunity for you to be bold and improve the article!
Atlant 12:51, 4 August 2006 (UTC)
Look through the history of the article to see if any sections have been deleted. Evidence of a deleted section may be indicated by a significant decrease in the number of bytes from one revision to the next. Usually vandalism is reverted, but sometimes it is overlooked and other editors start editing on the vandalized version. Users scanning for vandalism to revert usually look only at the last couple edits. H Padleckas (talk) 17:45, 24 May 2009 (UTC)

How is it delivered?[edit]

I wanted to know exactly what happens with the three holes in an outlet. Since voltage is a difference, and a circuit must be closed to receive it, does only one of the leads vary, or both, in opposite phases from each other? If the latter, does that mean connecting the same terminal from two different outlets produces no current? If the former, does that mean one of the terminals has no power? Does the ground terminal connect directly to the ground or a building's structure, as opposed to running through a power cable?Badmuthahubbard 20:33, 19 August 2006 (UTC)

Touching the ground wire will never cause you to get a shock, if it's truly grounded (let us hope). There is no way for current to flow up from ground and into you, and back down. The ground wire is just that, ground, electrically it's a part of the earth. The "hot" side is esentially a current being pushed at your house and pulled back to the power plant 60 times per second. It works a bit like a Newton's Cradle. And while this is all simplified, it's essentially true. Only 1 of the 3 holes is live, the other 2 are grounded, one is an enclosed wire ground (called neutral) which returns to the national grounding network (whatever that really may be...) And the other (the big one on the bottom) is attached to the cold water pipes and a big stick that goes about 10 feet into the ground below the house. ReignMan (talk) 19:44, 21 December 2007 (UTC)
The neutral/cold wire is grounded and the live/hot wire varies. You could say that the neutral wire 'has no power', in the sense that if you touch it you probably won't get a serious shock; but when you complete the circuit by plugging in a load, it carries just as much power as the live wire. The ground wire goes to a local ground in the building. It is there for safety, and normally carries no power. --Heron 20:48, 19 August 2006 (UTC)
P.S. There is a huge amount of detail at Domestic AC power plugs and sockets, and probably other places too. --Heron 20:50, 19 August 2006 (UTC)

twin lead[edit]

You have twisted pair but what about the twin lead we used to use for TV antennas? Some people used forms of twin lead for ham radio. Knob and tube and romex could be concidered twin lead as well. --Gbleem 13:54, 2 September 2006 (UTC)

I'm not following what does twin lead have to do with Alternating current. The twisted pair was shown to be a technique for reducing radiation loss, a by-product of alternating current. --Asbl 21:59, 2 September 2006 (UTC)

Who originated AC theory?[edit]

The article makes no mention of who first developed (or experimented with) the theory of alternating current...—Preceding unsigned comment added by 219.88.179.132 (talk) 11:29, 7 September 2006

re: Tesla was the first person to technically invent poly phase transformers which use AC, unless the lightning hitting the kite with a jar and key is counted as AC, so Tesla.. —Preceding unsigned comment added by 90.202.100.235 (talk) 12:42, 13 September 2008 (UTC)

positive and negitive[edit]

does alternating current have positive and negitive like direct current?--Falcon866 02:35, 5 January 2007 (UTC)

No. Every part of an AC circuit alternates continually between negative and positive. If you look at the symbol for an AC generator on a circuit diagram, you will see that it does not have + and - markings like a DC generator. In simple cases, the two wires coming from an AC generator are interchangeable. There are complex cases where they're not, but I won't go into that here. --Heron 21:02, 5 January 2007 (UTC)
So if both wires carrying AC are equivalent, what's the difference current and neutral blades on a polarized plug? —The preceding unsigned comment was added by 192.18.43.225 (talk) 21:48, 25 January 2007 (UTC).
The "hot" wire is connected to the smaller side of the polarized (American) plug. It carries a signal which oscillates between positive and negative with an RMS amplitude of about 120 volts. The larger plug is connected to the "neutral" wire which runs back to the electric companies generator where it is grounded. -AndrewBuck 22:55, 27 March 2007 (UTC)

Requested picture[edit]

The article on DC has an image showing the DC "symbol" that is used on electronics and such. I would assume there is a corresponding symbol for AC. I think it would be a good addition for the article to contrast it with DC. -AndrewBuck 22:49, 27 March 2007 (UTC)

I agree, I think this would be very useful. The corresponding symbol for AC is a tilde (~).CCW1946 (talk) 16:30, 9 July 2008 (UTC)

Three phase voltage just wrong[edit]

Here on the Wikipedia, where a dozen articles go into great and varying detail on the standardization of European utilization voltages, we (used to ) find the light-hearted statement that American utilization voltage is 3 phase 110 volts. Sorry, it's not - not three phase, and not 110 volts. You won't find a reference for this because it doesn't exist. I've taken it out again, it's not relevant to the example. There's no salvaging the commented-out paragraph and I recommend it be deleted. --Wtshymanski 21:13, 10 April 2007 (UTC)

And it's still wrong. A better place to discuss this would be electricity distribution, anyway. There are *very many* standardized sets of AC voltages, only a few of which appear at wall plugs. --Wtshymanski 17:32, 16 April 2007 (UTC)
Well, in fairness, in the United States, your most basic delivery to residential neighborhoods is 3 phase. If you look at the poles, they have 3 hot wires, 120 degrees out of phase, and a ground. If you try plugging in 2 metal grounded devices from 2 houses, or opposite sides of a large one, you'll get a shock. I'm no expert on delivery systems, but that's just what I'd consider the norm in the U.S. So perhaps the author thought that that was all there was... But as for 110 volts, that's only after the local step down transformers, the current on the wires is (in my area I believe) 7800V. ReignMan (talk) 19:44, 21 December 2007 (UTC)

Square-Wave equation is misleading[edit]

The equation Vrms=Vpeak is only true if centered about the x-axis. If a dc-offset is considered the equation is invalid. Duty cycle must then be taken into account. Consider a square wave with 50 percent duty cycle, peak voltage of 1 volt, centered at half a volt. Rms voltage is then 0.707... Someone tell me I have had too much coffee tonight, and that I am in error. —Preceding unsigned comment added by 24.9.208.230 (talk) 04:37, 30 November 2007 (UTC)

I think it's fairly clear from the article that unless otherwise specified, the discussion is about pure AC voltages. Mr. PIM (talk) 23:40, 21 September 2008 (UTC)
OK, I added a couple of words to emphasize that were talking about the case of no DC offset. Mr. PIM (talk) 23:45, 21 September 2008 (UTC)
You're missing the EE taught whole concept that AC power involves the delivery of an alternating polarity electrical power impulse, which can be altered by the addition more than 1 frequency of supply resulting in a power impulse supply voltage that vary in voltages and frequencies up to and including square wave supply impulse power. WFPMWFPM (talk) 19:50, 21 October 2008 (UTC)SeeFourier transform .WFPMWFPM (talk) 20:09, 21 October 2008 (UTC)

Wall-plug versus battery[edit]

Why doesn't this article say which is battery power and which is wall-plug power. I always forget. I can't be the only one can I? —Preceding unsigned comment added by 81.138.12.194 (talk) 11:13, 1 February 2008 (UTC)

It doesn't explicitly put it in those terms but if you read this article and the direct current article it is made pretty damn clean what each is used for. Plugwash (talk) 23:44, 1 February 2008 (UTC)

Dating wrong[edit]

The date of the first modern A/C station is wrong. The first such station was built by Ferranti at Deptford near London in 1891. It produced an A/C 10Kv supply, with transforner stations for each street served. Chasnor15 (talk) 11:12, 28 March 2008 (UTC)

High Voltage DC[edit]

"HVDC systems tend to be more expensive and less efficient than transformers." This statement is wrong (or at least needs some justification), otherwise why would they use HVDC. HVDC systems can be more efficient at transporting large quantities of power, as there is no reactive power. The efficiency of the power electronics is increasing annually as new GTO's/IGBT's are developed. —Preceding unsigned comment added by 82.30.33.111 (talk) 15:41, 27 April 2008 (UTC)

It's more efficient because
  1. The V value is the DC voltage value and not the RMS value of the AC voltage. and
  2. The I value for the same power transmission value is less and therefor the transmission line IsquaredR electric power loss is less.
WFPMWFPM (talk) 11:20, 20 October 2008 (UTC)

City lights blinking[edit]

Photo caption: "City lights viewed in a motion blurred exposure. The AC blinking causes the lines to be dotted rather than continuous."

This should be considered highly suspect as most city lights are incandescent bulbs, which emit light through the relatively steady level of heat that builds up in a metal filament. The digital camera used to take the photo is a much more likely culprit.71.244.17.134 (talk) 14:57, 21 September 2008 (UTC)

What is much more suspect is a drive-by editor who thinks most city lights are incandescent. I like the picture because any more literal representation is going to be dull, and the wavyness of the traces somewhat suggests sinusoid shapes. —Preceding unsigned comment added by Wtshymanski (talkcontribs) 16:43, 21 September 2008
Please remember to Assume Good Faith and to not resort to name calling, such as "drive-by editor". Mr. PIM (talk) 23:04, 21 September 2008 (UTC)

Back to the original conversation, I do not see the point. Are you trying to say that the length of time it takes an incandescent light bulb to light up and to go dark is more than 1/60th of a second (or 1/50th of a second if the photo was taken in countries where the frequency is 50 Hz)? Mr. PIM (talk) 23:07, 21 September 2008 (UTC)

It might be worth mentioning in this discussion that fluorescent and other lights with an almost instantaneous on/off brightness switch, flicker at twice the AC supply-frequency (because they light regardless of whether the AC voltage is positive or negative). So on a 50hz supply, they flicker at 100hz, and those countries with a 60hz supply have a 120hz flicker.PrinceGaz (talk) 03:48, 11 February 2009 (UTC)

Phase difference[edit]

I removed the phase factor from "the power transmitted is equal to the product of the current, the voltage and the cosine of the phase difference φ ( P = IV \cos \phi)" because it was not really relevant to the reason for high voltages in transmission, but it should be mentioned somewhere, with an explanation that the phase in question is that between V & I. Dbfirs 21:16, 22 November 2008 (UTC)

The "Power and root mean square" section of this article quite misleading. As of right now, this section is written as if the electric loads were purely resistive. If there's any reactive component to the loads, then the equations and calculations do not apply and have to be modified as in the preceding Talk discussion but not currently present in (apparently deleted from) the article. Furthermore, I consider that in the most fundamental sense at any time t, real power at a that time, P(t), equals voltage V(t) times current I(t), both at time t.

P(t) = V(t) I(t)

The voltage averaged over time = Vrms and the current average over time = Irms. The average power then is derived by integrating over (at least) one full time period and Vrms and Irms inserted into the result. H Padleckas (talk) 18:24, 24 May 2009 (UTC)
I agree with you, H Padleckas, that the power section currently deals only with resistive loads, but I think there is no need to go into reactive loads because that detail is not necessary for this article. With purely reactive loads, power is delvered to the load for half the cycle (when the sign of the current and the sign of the voltage are the same), and the power is returned by the load to the source for the other half of the cycle (when the sign of the current and the sign of the voltage are opposite). For resistive loads the power is always delivered to the load for the entire cycle. I therefore add the word "delivered" in this edit. I hope this addresses your concern. Mr. PIM (talk) 20:41, 22 June 2009 (UTC)

Unreferenced[edit]

Hey, just added {{Unreferenced}} to article. I noticed there were no citations. Please add some. Thanks! 68.175.84.142 (talk) 21:58, 27 January 2009 (UTC) (If you have any questions, please direct them to User:Riotrocket8676. Thanks!

Whilst I appreciate the Wikipedia requirement for confirmation of information from recognised sources, I really don't see the point of adding the tag to this article. There are literally thousands of textbooks which confirm the information given, and it can readily be checked from the external links. If there is a particular point in dispute, then a citation should be provided for that point, otherwise the article is just common knowledge, checkable from thousands of sources (including many of the links stated at the end) - does Riotrocket8676 want us to list them all? Dbfirs 23:23, 27 January 2009 (UTC)

I meant inline citations. Reclassified.68.175.84.142 (talk) 01:00, 2 February 2009 (UTC)

Intro Layout Improvement[edit]

Due to the postion of the 'city lights' picture, there was a lot of white space, so I've moved it down, below the 'History' sub-heading, and slightly enlarged the default size of the 'Westinghouse Early AC System' diagram so they match. This isn't ideal but I think it looks a lot better.
In a general observation, I find in the Wikipedia technical articles that a lot of pages have poor layout, and this makes them harder to read.

Ideally I believe all text should be aligned on the left margin and graphics generally on the right side, if they're not wide enough to be centred. --220.101.28.25 (talk) 16:43, 31 October 2009 (UTC)

Coaxial Cable[edit]

Please do not delete additions unless you are an expert in the subject. "Seems dubious" is not sufficient grounds for vandalism. But I will resist the temptation to play silly games until I have found a proper reference :) —Preceding unsigned comment added by 82.45.185.126 (talk) 19:23, 1 March 2010 (UTC)

Descriptions of 120/208, 277/480, etc.[edit]

Might I ask someone to add a description of what 120/208, 277/480 refers to? I only understand single-phase, but I think it's phase-to-neutral (ground) versus phase-to-phase? Is WikiAnswers correct? [1] MrBell (talk) 22:59, 22 April 2010 (UTC)

That's really more a convention for describing distribution systems than a point for this article, which I think is meant to talk more about fundamentals. If there's two voltages available in the same distribution system, it's often the case the system voltage is given with a slash or other dual indication. In single-phase systems there is a center tap and the voltages betweeen the two energized conductors are twice the voltage between an energized conductor and the center tap - so we get designations such as 120/240. In three phase systems, the voltage between any two conductors is sqrt(3) times the voltage between a conductor and the "neutral" reference point - so you might have a distritbution system designated "120/208" - 120 volt loads can be connected from an energized conductor to the system neutral point, and 208 volt (single- or three-phase loads) can be connected to the energized conductors.
You find the same thing at medium voltages used for distribution, for example you may find a system designated 24.49Y/14.4 kV - if you have industrial customers in the area who need 3-phase power, you run 3 wires out and there's 24.49 kV between the wires, but if there's only residential loads, one pair of wires (or a wire and an earth return) suffices, and the single-phase transformers are connected single-phase to neutral (ground) at 14.4 kV. --Wtshymanski (talk) 13:28, 23 April 2010 (UTC)
Great explanation, thanks. Based on your comment, would you recommend that this info be proposed/added to Electricity distribution instead of here? MrBell (talk) 15:12, 23 April 2010 (UTC)

About a link[edit]

I added a link to Garyfallidou.org/en_electricity.html, a page containing a video which explains (to kids) how free electrons act in a simple circuit. In case of: No current, DC current and AC current. The link removed by Wtshymanski. I believe that Wikipedia (any encyclopedia) is for people (specially kids) who are trying to get knowledge and not for people who already have the Knowledge. The link added to Electric current-Direct Current-Alternating Current. Removed from Electric current - Alternating Current. Lambrosus —Preceding unsigned comment added by Lambrosus (talkcontribs) 18:05, 26 May 2010 (UTC)


Explanation about neutral 0 and electrocution[edit]

What is the reason for an AC circuit to have a neutral wire (0)? I mean the alternative current is passing through the consumator and returns usually 50 times per second (50HZ) but why it won't work if the signal don't return? Does the return signal contains an unused energy (like some watts which the consumator don't need)? Also if I touch a phase/line cable where AC or DC is applied and I am in air will the current hit me and in what situation? Or if I am on the ground but with a STRONG ISULATOR which don't allow current to pass through my body to the ground. As far as I know the current always needs a return path and if lets say 300 kilovolts and 100 ampers of current is applied will it do me something if it cannot return anywhere? Even if I am in space (vacuum)? :)))))))) =) --Leonardo Da Vinci (talk) 11:11, 1 December 2010 (UTC)

Article talk pages are about improvements to the article. You can ask questions at the help desk. You may want to pick up a fundamental textbook on electricity in your primary language, a review of which would probably save you hours of typing questions here. --Wtshymanski (talk) 14:40, 1 December 2010 (UTC)

Variation of AC voltage with time[edit]

Although the voltage of a sinusoidal wave varies continuously with time, still we don't observe any change in the intensity of the visible light sources.Why? — Preceding unsigned comment added by 117.227.65.225 (talk) 17:53, 30 June 2012 (UTC)

Because most visible light sources operate at too high of a frequency. Even if the visible light were coherent, as in a visible light laser, the wavelength is much too small for the spatial variations of the voltage to be optically discerned (except with very specialized equipment). Also, please note the existence of periodic variable stars. It's not technically true that visible light sources don't vary in intensity, though at a macro-level, any correlation between intensity of fluctuations and ideal sinusoid AC waveforms tends to be rather weak.siNkarma86—Expert Sectioneer of Wikipedia
86 = 19+9+14 + karma = 19+9+14 + talk
19:40, 7 April 2013 (UTC)

Electric and magnetic field time variation of an alternating current and the role of displacement current[edit]

It appears that little is said about the role of the E and B fields of alternating current in this article. Furthermore, analysis reveals that displacement current (based on time variations of the electric field) actually corresponds to the jerk (physics) of electrons (based on time variations of force on each electron, as determined by the time-varying electric field). If sin(x) is the velocity in arbitrary units, then -sin(x), the second time derivative of sin(x), is jerk in arbitrary units, given that we set t'=1. As it turns out, for an alternating current system, the derivative of velocity, cos(x), and the derivative of jerk, -cos(x), cancel out exactly, meaning that their variations compensate for each other directly. Displacement current and electron current can be seen as flowing in opposite directions at a given point in an alternating current system. Please advise on the possibility on incorporating source material regarding E, B, D, H, P, and M fields in alternating circuits. Sincerely, siNkarma86—Expert Sectioneer of Wikipedia
86 = 19+9+14 + karma = 19+9+14 + talk
19:40, 7 April 2013 (UTC)

Current Flow[edit]

Commonname deals with article titles, not article content. And Charge is the term used when describing current, not current itself. --Kyohyi (talk) 17:05, 11 October 2013 (UTC)

Current is the term used when dealing with current.
Can you find one credible textbook for engineering applications of 3 phase AC (as described in the section you changed) that avoids using 'current' in this sense in favour of charge? Andy Dingley (talk) 17:23, 11 October 2013 (UTC)
Actually Charge is the term, it's in the definition. Using the term current to describe the term current is circular. Now I'm not dead set on the use of charge as a term, however I am against the use of the expression Current Flow. It's jargon and isn't defined in electrical texts. And the textbook that I have handy doesn't even describe 3 phase AC in terms of current, it defines it in terms of voltage and power. --Kyohyi (talk) 17:56, 11 October 2013 (UTC)
I don't care that you're against the term current flow. I care that many reliable sources do happily use it. Andy Dingley (talk) 18:11, 11 October 2013 (UTC)
Which would be perfectly fine if any of them defined it. --Kyohyi (talk) 18:14, 11 October 2013 (UTC)
This discussion seems to have started on Electric Current. I'd like to suggest that the discussion stay there until it is resolved.Constant314 (talk) 01:30, 15 October 2013 (UTC)