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I should mention that electricians are some of the most nitpicky people on the planet... Comes with the territory! klim, I hope we haven't completely scared you off, Scott35 is the moderator of our Electrical Theory section , wait for his reply to this, he has a way of explaining things. As far as editing, I would, but I'd want Scott, Bill, Steve, Don and Frank to proofread mine! Whew! [This message has been edited by sparky66wv (edited 05-11-2001).]
-Virgil Residential/Commercial Inspector 5 Star Inspections Member IAEI
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Exactly Sparky66!
With respect to the number of phases that a particular system has, for all practical purposes we are really refering to the number of sine waves present. With single phase, we have one sine wave. If we could slow time down and look at the current flow on a single phase circuit, at a point where current is flowing "IN" one of the conductors, you can bet the farm that it is flowing "OUT" the other.
Because we only have two conductors that we can measure a potential difference between, we can only have one single voltage. The amplitude of the voltage is the same throughout the circuit at any point in time.
Conversely, on a 3 phase system we have three seperate sine waves. If we superimpose these sine waves over each other, we would see that each phase is typically 120 degrees out from the next.
Matt
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Hi everyone. In my opinion I think the text is great! There's really no need to throw a bunch of tech info at persons unfamiliar to the whole thing - it scares normal people We, as electricians, and especially me for example, tend to want endless and complete details conserning our field's technical issues. This is the way we should be!! The document was, to me, well written and easilly understandable by the general public. It's just substandard to us sparkys because it lacks tons of detail! [and we've seen that type of system a million times before]. Maybe one thing could be changed - in order to keep confusion down: instead of saying the 240 VAC conductors are 180 degrees out of phase, just say that there's 240 volts between them. Keep it simple on that part so the people can understand and don't get stuck in never-never land thinking about math and theory. [it also keeps the flames from sparkys like myself, to a minimum ]. Now I'm not too sure if that stuff was in the original text, or just something generated here - sorry!! Scale of 1-10, I give it 10! Virgil, You've nailed that 1 phase system!! Great job!!! Nothing I could add to this thread that would be any different than what's already here, so I'll continue bouncing around the forum. P.S. I will be posting a few schematics to the theory area tonight - a couple are on those 6 and 9 phase rectifier transformers shown in the pictures. Scott SET
Scott " 35 " Thompson Just Say NO To Green Eggs And Ham!
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those 6 and 9 phase rectifier transformers Hey Scott, you tryin' to scare away the laymen? FYI: 6 and 9 phase rectifier transformers are used to convert AC power to DC power more smoothly than three phase rectifier transformers. Case in point: My old TI30 calculator won't run on a 9V wallwart (single phase rectifier transformer in miniature...) due to the poor DC power quality, which demonstrates why these exotic creatures are useful in todays electronic world.
-Virgil Residential/Commercial Inspector 5 Star Inspections Member IAEI
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klim; just a suggestion here, might you consider letting the forum access this 8000 word file? perhaps an adobe acrobat deal? like Virgil said, we are kinda knit picky, and you'll get 10x the feedback utilizing a bunch of us besides, i wanna get to the equopotential plane part.....
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Klim, Personally I like your wording so far including the way you describe getting 240 volts. It should be easily understood by most everyone. I do have a suggestion about changing something though. That way, if an exposed part of the equipment becomes energized due to a wiring fault inside the equipment the safety ground connection causes the hot connection to be directly connected to earth, and the fuse or circuit breaker would shut down power to the circuit. I think the word 'earth' should be changed possibly to 'service ground'. It's true that the Hot connection will be connected to earth, but that in itself really won't do anything. What causes the fuse or circuit breaker to shut down is the fact that it is now connected to the neutral coming from the service. Perhaps someone can explain it better than I, but I feel that it is an important point to be made and it would be best if it was as correct as possible and not perpetuating a popular misnomer. Are any in agreement? Bill
Bill
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Bill; a strong second here. but now we would owe klim's book an explanation of why agricultural building need to be overgrounded. (de plane, de plane Boss.....)
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Originally posted by Matt M: Huh? Out of phase? But isn't this single phase? No, sir. I discussed this with Scott35 before. I say that if he can have 9 phases, then I can have two. Although drawn from one phase, the center tap on the secondary winding splits it into two phases. I called them poles to avoid having to argue with Scott. A single phase, AC service drop consists of two ungrounded (hot) conductors, with a potential difference of 240 volts nominal between them, But you said nothing of why there are 240 between them. It's not like one is +120 V and the other -120 V. and a grounded (neutral) conductor with a potential difference of 120 volts nominal between it and either one of the two ungrounded conductors. You just glossed over one technicality and dug into two more. I also have a little trouble with the word "carry" with regard to voltage. I think a more accurate term would be "supply". Yeah, supply/provide/whatever. Carry is for current. when referring to a nominal voltage such as 120, you cannot really say that an individual conductor supplies 120 volts, Did you forget to mention that this is a sinusoidal waveform and 120 V is the RMS? No, really, I wasn't trying to overcomplicate it. I was trying to leave out the details that don't seem important to casual users without saying something wrong. ... like focusing on the importance of the neutral to complete the circuit rather than a ground rod.
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My Mom knows first hand of what can happen in a dairy milk parlor. I got 43V RMS from the milking stall to the wet drain after she complained of getting shocked.
So where does this stray (or floating) voltage come from? The soil/concrete/water/steel acting as a battery?
Bonding the milking stall to the ground bus cured that one... down to 1.5V RMS now... about 50 years too late for an equipotential plane though... (Jack hammer time?...not me!)
-Virgil Residential/Commercial Inspector 5 Star Inspections Member IAEI
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Anonymous
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Originally posted by sparky66wv: [B]If they were 180 degrees out of phase, you would have nothing.
Sorry to burst your bubble..
Where's Scott? Hmmm, how would he handle this... You didn't burst my bubble because I am correct. Scott appears to agree (or he's scared to upset me). The reality is that the secondary coil in the transformer is center tapped to neutral (grounded conductor) in a 240V single phase system... the center tap splits up the two 120V legs. Heh, heh. Well, those two legs are 180 degrees out of phase. Notice that the transformer outside your home is tapped to only one ungrounded high voltage conductor, hence single phase. Notice that Scott's 9 phase transformer is tapped on just three phases, hence three phase. Ooops! First, technically, there is no neutral in a single phase system. The white (or natural grey) wire is called the "grounded conductor". Give us a break! We know what we mean. We know the technical terms. This is a horse book were talking about!! Oh, and by the way, there is no such thing as natural grey thermoplastic insulation. This is not to be confused with the "ground" (green or bare wire) which is called the "equipment grounding conductor".
We know. That was explained. Did you read the chapter? Has you user ID been taken over by a newbie?
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