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Re: [Shop-talk] Yet Another Wiring Question

To: "Robert E. Shlafer" <pilotrob@webtv.net>
Subject: Re: [Shop-talk] Yet Another Wiring Question
From: "Randall" <tr3driver@ca.rr.com>
Date: Tue, 30 Jun 2009 19:50:14 -0700
> My AC circuits prof would box your ears for that.  There's one phase.
> Choosing the neutral as a measuring point doesn't magically give you
> two.  (Were there really two phases, you wouldn't be able to run 240V
> loads from the system.)

Actually, it's the other way around.  If they weren't different phases,
there would be no voltage at all between them.  But in fact they are
different, by 180 degrees.

One phase looks kind of like this crude ASCII art :
  _       _
 / \     / \
|   |   |   |
    |   |   |   |
     \_/     \_/

While the other is
      _       _
     / \     / \
    |   |   |   |
|   |   |   |
 \_/     \_/

Not the same at all.  

And the fact you can add them together to get twice the voltage proves that
they are 180 degrees apart.  The same thing is not true in a 3-phase system,
because the 3 legs are each 120 degrees (360/3) apart.

Furthermore it is possible to have a 2-phase system where the two legs are
not 180 degrees apart, but it's not used much.

Randall
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