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Old 12-17-2009, 03:37 PM  
Blue Jay
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On a normal range the only time that 110V would come into play would be with the burners on low it would then use the 110V and thus the neutral would come into use and you would have current flow on it but higher settings would use 220V with no neutral involvement.



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Old 12-17-2009, 05:06 PM  
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The is no dispute that if you have any 120 volt loads there can be voltage on the neutral. To have a reacative load on one hot and an inductive load on the other hot you would have to have two separate 120 volt loads. My comment was with regards to 240 volt loads. If only 240 volt loads are present there is no current on the neutral mainly beacause the neutral is not even connected to the loads.



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Old 12-17-2009, 06:11 PM  
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Joe:
To say that there's no current in the neutral wire of a 220 volt circuit if the neutral wire isn't connected is trivial. I agree completely. You can't have any current through a non-existant wire. But, that wasn't the point I was making when you originally disagreed.

The point I was making (and the question that's confounding me right now) is as follows:

1. Imagine you have a duplex 110 volt receptacle in a kitchen, and the tabs between the receptacles have been cut to allow the upper receptacle to be powered by the black wire and the lower receptacle to be powered by the red wire. The two receptacles share the same neutral wire back to the panel.

2. Now imagine you were to buy two identical electric toasters and plug one into each of those two receptacles.

3. If you were to turn on both toasters, then you'd have a purely resistive load between the black and white and between the red and white. Since the black and white amperage and current sine waves are 180 degrees out of phase, then theoretically, the amperage and current sine waves will cancel when they meet at the white wire, and there should be no voltage or current whatsoever in the white wire (theoretically, at least).

4. Now imagine we unplugged one toaster and plugged a big capacitive load (like a TV set) into that receptacle instead.

5. Now, the red and black amperage sine waves will no longer cancel each other out. That's because if you consider the two plates of a capacitor, the current OUT of the second plate of the capacitor is going to be highest when the RATE OF CHANGE in voltage of the first plate is highest, and that happens when the voltage sine wave is actually at 0 (zero) volts, like this:



In the above diagram for a capacitor, the red current sine wave (i) out of the capacitor precedes the blue applied voltage sine wave (e), so the two are no longer in phase as they are with a resistor.

You see that for a capacitor, the current flow out of the capacitor is highest when the RATE OF CHANGE in voltage in the first plate is highest, and that actually occurs when the voltage crosses the zero voltage line. So, the current out of the capacitor is highest when the voltage is at zero volts, and that means that the current sine wave (i) precedes the voltage sine wave (e) by 90 degrees.

(If anyone doesn't understand the above 2 or 3 paragraphs, Google the phrase "ELI the ICEman" without quotes, and you should find plenty on the subject.)

6. So, with one toaster replaced with a TV set, then the capacitive reactance of the TV set causes the current sine wave to occur earlier than the applied voltage sine wave. Since the other leg (the toaster leg) voltage and sine waves are still in sync, then the current sine waves from the two legs will no longer cancel each other out when they meet at the white wire.

7. If the two current sine waves occur at a different times, they won't cancel each other out, and that means there HAS TO BE some resulting current in the white wire.

AND, HERE'S WHAT'S CONFOUNDING ME:

With the TV set plugged in, do the red and black voltage sine waves still cancel each other out? It seems to me that they can't because then you'd have current in the white neutral wire without any driving voltage.

(It seems to me that the voltage sine wave won't be affected as it goes through the capacitor. As the voltage of the first plate of the capacitor increases, or decreases, it'll induce the same voltage in the second plate of the capacitor. So, it seems at first blush that the second plate of the capacitor will always be at the same voltage as the first plate of the capacitor, which would mean that the voltage sine wave would be unaffected as it passes through the capacitor.)

And, if none of the electricians in here can explain this to me, then I'm gonna take me a drive down to the U of M to visit some old profs. The horse is volunteering to go instead cuz he understands the problem completely, but this is a man's job.

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Old 12-18-2009, 04:51 PM  
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I understand that the horse heard it from the cow.....I'm udderly confused.

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Old 12-18-2009, 07:54 PM  
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Quote:
Originally Posted by slownsteady View Post
I understand that the horse heard it from the cow.....I'm udderly confused.
That's what happens when you let an engineer roam free on a message board.
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Old 12-20-2009, 12:17 PM  
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Now your getting too technical when you start throwing power factor into it. Put some PCs on the line and watch the netrual current go crazy from harmonics. I have seen 3 phase power with 100 amps on the neutral when all the phases only had between 70-80 amps each.

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Old 12-22-2009, 10:45 PM  
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Patience.

I've contacted a prof in the Electrical Engineering Department at the U of M. I explained the problem over the phone, but I followed up with an e-mail that he could refer to and pass on to someone else.

He's e-mailed me back saying that he thinks he understands the problem, but it's not really his area of expertise, so he's going to talk to some other people and get back to me.

If anyone wants, I can copy and paste the e-mails in here.

Otherwise, I'll post whatever I find out when I get his response.

PS:
This is not a difficult problem to understand. If impedance causes the amperage sine wave to go out of phase with the voltage sine wave, then the result is that there'll be a net amperage waveform of some sort in the white wire where the two amperage sine waves from the TV and toaster meet. But the voltage sine waves from the TV and toaster should still supposedly cancel each other out, so there shouldn't be any voltage in the white wire.

And, that's screwing with my head because you can't have current in the white wire without there being some kind of voltage in that wire to drive that current.

And, if you don't understand the difficulty, then just don't worry about it because it's got nothing to do with whether the original poster's stove is wired properly. I've run face-first into a problem I can't explain, and so I'm trying to figure it out.

Let's just wait and see what the prof at the U of M finds out, if anything.

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Old 12-30-2009, 07:35 PM  
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Sorry to abscond without following up til now.

I have ripped out this cable, and a good many others in this old house.

For this range I have installed a new 4-conductor copper cable - three awg6 conductors (red, blk, wht neutral) and one awg10 ground wire.
Two 50A ganged breakers.

End of story!

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Old 12-30-2009, 09:37 PM  
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I guess this makes nestor the official bulldog of this forum. I don't think he's gonna let go til he chews this one up!

Nestor; that's a compliment.

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Old 12-31-2009, 06:59 AM  
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Well texas...sounds like you did the sane thing and upgraded. Now you can move on and tackle the next project, hope we didn't scare ya away.



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