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.