DIY Home Improvement, Remodeling & Repair Forum > Range wiring

01-07-2010, 09:52 AM
Nestor_Kelebay
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Join Date: Mar 2009
Location: Winnipeg, Manitoba
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OK, here's a progress report:

I have gotten three e-mails from Arkady Major, a professor of electrical engineering at the U of M so far. They are as follows:

Hello Nestor,
I think I understand the question, but I can not answer it on my own.
I will consult with my more knowledgebale colleagues and will get you
regards

Hello Nestor,
just a quick thought: aren't the two hot wires 120 degrees out of phase?
This would solve the problem.
regards

Hello Nestor,
> I asked another colleague of mine and you are right, the residential
> power is derived from a single phase (~7.2kV) that is down converted by
> a transformer to 220V. As you mentioned, this transformer has a middle
> tap that produces two hot wires at 110 V each and 180 degrees out of
> phase. Well, at least I managed to get through this stage! I'd say it is
> a good start.
> Unfortunately I was in a rush and did not have enough time to bug him
> about your main question. But I will hunt him down again to get the
> regards

for people who just tuned in:
I initially e-mailed Arkady a copy of the post where the duplex receptacle in a kitchen was wired with a black wire to one outlet, a red wire to the other outlet and shared a common neutral. Then, if we plug identical resistive loads into both outlets, the voltage and current sine waves would both cancel each other out in the neutral wire, and there shouldn't be any current or voltage in the white wire. But, if we plug a resistive load (like a toaster) into one outlet and a reactive load (like an electric motor or TV set) into the other outlet, then the question becomes: "What happens in that neutral wire?" The current sine waves won't cancel out any more because they'll arrive at the white wire at slightly different times (cuz of the reactance), and so there has to be some "net" current in the white wire. If we still presume the voltage sine waves cancel out, then there theoretically should be no voltage in the white wire. And, the problem then becomes: "How can we have current in that white wire with no voltage to drive it?"

I can see that Arkady realizes this is an interesting problem too. Otherwise he just would have barfed out some gobbledy-gook about reactance and phase relations just to get rid of me. The fact that he's trying to find out the answer means he fully understands the problem and is interested in the explanation too. I'll post back in here when Arkady gets back to me.

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Last edited by Nestor_Kelebay; 01-07-2010 at 10:09 AM.