On 11/25/2013 08:31 AM, snipped-for-privacy@optonline.net wrote: [snip]
I'm not an expert nor do I play one on usenet but...
IIRC, current carrying (line and neutral) conductors in a conduit must be insulated.
This is usenet and if I'm wrong I'll be corrected shortly. ;-)
I do want to thank those who responded to my initial question about how the center tap gets referenced to ground.
I think we get sidetracked with the use of phase to mean two different thin gs. What if you put ground on the bottom of the secondary instead of the c enter? Hee, hee.
But, at the risk of another rabbit hole, electrons don't actually get pulle d from ground and sent to your house, unless you have a DC supply. In AC, e lectrons merely bounce back and forth a short distance, like a millionth of a meter. The wave travels, but not the electrons. IIRC.
The earth does not complete the circuit. Wires complete the circuit.
The electrons that flow are in the wire.
If you had DC, an electron flowing out one end of a wire would be matched by an electron flowing in the other end. A single electron may not move very far, it can be replaced by another electron. A property of a metal is that there are electrons that are not tightly bound that can migrate.
With AC, electrons move in one direction, then the other.
The do have a wire for any intentional electrical path.
Since early power distribution days there is a metal connection for the entire path. Earth is not an intentional path.
The earth is not used as an intentional path.
The connection to earth is used to limit the voltage between the wires and the earth. The earth is also a sink for lightning and similar events, and is used to trip overcurrent protection with crossed wires.
The earth is not allowed to be a path to trip a circuit breaker in your house if there is a short between a hot wire and ground at, for instance, a drill. The short circuit current goes through the N-G bond at the service and returns to the utility transformer through the service neutral. The earth is not allowed to be the path because it is not an effective path.
Rather flawed.
Bud, until recently I would have agreed with you. But, whomever wrote this web page obviously knows something about electric power generation and distribution and seems to disagree:
http://t And what about this "ground," as mentioned above? 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. (Car manufacturers do something similar; they use the metal body of the car as one of the wires in the car's electrical system and attach the negative pole of the battery to the car's body.) "Ground" in the power distribution grid is literally "the ground" that's all around you when you are walking outside. It is the dirt, rocks, groundwater, etc., of the earth.
I don't think he could have said it any clearer.
First of all, in North America, the typical p[ower supply is NOT 2 phase. It is center tapped single phase. You have a line1, a line2 and a neutral - the neutral being shared between the two lines. If the load is ballanced between the 2 "sides" there is no current in the neutral. The neutral is regerenced to ground for safety reasons.
In early reural electrification in the USA, single wire distribution was used - using "earth return" It worked, but was fraught with problems, and is virtually unheard of today..
Today's power distribution is 3 phase - with each phase feeding a separate distribution transformer - which has a center tapped secondary for residential power. 3 phase is supplied for industry and some multi-unit residential buildings which run 120/208 instead of
120/240. This is because 3 phase power is 120 degrees phase to phase. because the generating system IS 3 phase, there can not be 2 "phases" 180 degrees apart.Line1 and Line2 are generally red and black, with the neutral white and safety ground bare or green
I'm glad you found that, because there MUST be a complete circuit for current to flow (assuming an imbalance, as someone else noted).
The fact that the earth isn't obviously a "wire" is lost on some people who simply assume earth is ground potential and that's that.
But, that's OK.
That's because *both* ways of thinking work just fine, simply because the earth contains more electrons than anything on earth (which goes without saying). It's like the car frame example. Exactly. Only on a huge scale.
So, both concepts work simply because earth and the car frame are special things that don't look like wires, but, they act both like zero potential and like wires.
Specifically, the earth is both a zero potential, and a huge conductor back to the power company.
As Gallileo supposedly said on his deathbed to those who couldn't fathom the wonders of the earth ... "and yet, it does".
Heh heh ... Let's just agree to disagree. :)
I understand your argument, and you understand mine.
I'm saying the earth can be thought of correctly either as zero potential, or, as an absolutely humongous conductor back to the power company.
Both explanations work just fine:
- For you, you prefer to think of the earth as absolute zero potential.
- For me, I prefer to think of the earth as the return path to the power supply.
Both are perfectly valid, so, my only objection is you telling me that I don't understand.
I'd be perfectly happy to be wrong, but, I think I *do* understand your point (and I agree with you); but I think you don't agree with me. So, we'll never get anywhere under those circumstances.
So, let's just agree that I think you're right and I think I'm right, and that you think you're right and that I'm wrong. That's OK.
BTW, a thought-provoking question would be: Q: Where do you think the power company gets its electrons from anyway?
This is a good thought-provoking point.
The electrons do get bounced back and forth, but, isn't there "current" in so much that *work* is being done, which requires the electrons to actually "move"?
You might as well forget trying to explain that in most of the US the power comes in to the house as a split single phase. Also that unlike a car and much of the electronics where the frame/ground is often part of the circuit, the AC power does not use the ground for anything but safety and not one return leg. There are a couple on here that will never get it.
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.)
And just before that, the author, said:
"There are four wires coming out of every power plant: the three phases plus a neutral or ground common to all three."
That sentence alone shows that he doesn't know what he's talking about. A netural or ground wire are not the same thing. And even if they were, if the earth were used as the return path, then why would you need the 4th wire? The 4th wire carries the unbalanced current. The current is flowing in the 3 phase wires and neutral, not the ground.
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.
Maybe that's odd, for the USA though, 'cuz everyone is saying that the neutral is normally bare.
This is probably not called for.
I think my only mistake so far was "assuming" the lines coming into the home were 120 degrees out of phase (because I understood distribution but not the center-tapped transformer stuff). I now know they are
180 degrees out of sync with each other (because they come from the center tapped transformer which is fed only one of the distribution lines).The only other place where you and I disagree is that you don't consider the ground going back to the power company, whereas I do, and so do some references - and yet - I also allow your characterization of the ground being simply something that you can't change the potential of.
So, I think I don't need to go back to school so much as I simply disagree with you on a relatively minor point, which is how the circuit is completed.
On everything else, we agree, it seems, so, why do you incessantly (three times so far) tell me to go back to school?
We all get along here because we treat each other with respect.
I don't disagree.
It seems to me that if the load is imbalanced on circuit A versus circuit B (which is almost certainly likely to happen at some time or another), then there *will* be current in the neutral. Period.
If there is current, and if there is resistance, there is a potential. Period.
So, it seems to me, it's a mighty good idea to insulate the neutral. Clearly mine is well insulated.
It would be nice to see pictures from other typical homeowners in the USA as to whether theirs is insulated or not.
As has been explained a dozen times now, there is a complete circuit and under normal conditions, the earth is *not* part of it. You continue to ignore the *neutral" and the fact that with a balanced 3 phase load, the entire current flows in the 3 phase conductors.
Nonsense. You and Nestork are claiming that the power company delivers power using the earth as one of the conductor that complete the circuit. That isn't an alternate way of thinking, it's just wrong.
More obfuscation and confusion.
Wrong.
Gallileo didn't know much about electricity, did he?
I don't see anyone here denying that it's called "split-phase". The transformer splits a single PRIMARY phase. What generally happens when you split something? Do you still have just one? What's at issue is that you have two legs that are
180 degrees out of phase with each other. That simple true statement is where all the diagreement began. You can see two voltage waveforms 180 deg out of phase on a scope. If they were not out of phase by 180 deg, you would not get 240V. Here, from two electrical eqpt manufacturers that talk about two phases, 180 deg out of phase:And the IEEE clearly agrees that there are in fact two phases present. From a paper presented at a recent IEEE power engineering conference:
"Which now brings into focus the reality that standard 120/240 secondary sy stems are not single phase line to ground systems, instead they are three w ire 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 s econdary phases are separated by 180 degrees instead of three phases separa ted by 120 degrees."
Are IEEE power engineers and electrical eqpt manufacturers wrong?
I'm still waiting for someone on the other side of this to give their definition of "phase" and why if one can see two phases on a scope, there are not in fact two phases present.
There isn't an argument, John is right.
The problem is the earth isn't used as a humongous conductor by the power plant.
It is zero potential relative to the grounded neutral. That doesn't mean there is current flowing in the earth. To have something at zero potential doesn't even require a circuit. Take a metal cabinet sitting on an insulator and hook a wire from it to another metal object, or a neutral, a 120V hot wire, a 7KV primary. They are now at the same potential and no current is flowing.
They are *not* both valid. You have it wrong.
Sigh....
On this point John is correct, and you still have it wrong.
nning to the house.
The bare wire is the ground wire.
out of phase so the difference between them is 240 volts."
Tell that to my lying scope. You put the two hot legs of the split-phase service on a scope and what do you see? Two phases that differ by 180 degrees. If they didn't differ by
180 degrees, you would not have 240V. It's every bit as real as seeing 3 phases on a scope that are 120 deg seperate.White papers/app notes from two electrical eqpt manufacturers:
IEEE peer reviewed paper delivered at a recent power engineering conference :
"Which now brings into focus the reality that standard 120/240 secondary sy stems are not single phase line to ground systems, instead they are three w ire 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 s econdary phases are separated by 180 degrees instead of three phases separa ted by 120 degrees. "
The only time I've ever seen a bare neutral is in a service entrance cable between the meter and the breaker panel.
And while in most areas it meets code to use service entrance cable, I would only use conduit.
I don't believe anyone has said the neutral is not insulated.
ONLY the ground can be Uninsulated or GREEN or GREEN and YELLOW The Neutral is generally white and the 2 actives are black or red.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.