Subject: Re: 220V wiring question

From: [email-masked] (Chris Lewis)
Date: Thu, 13 Feb 1997 13:34:04 GMT

In article <[email-masked]>,
Tom Gauldin <[email-masked]> wrote:
>[email-masked] (Jim Jones) wrote:
>
>>>> >
>>>> >Not to put too fine a point on this, Jerald, but this is an error in
>>>> >your otherwise fine post.
>>>> >
>>>> >The two phases you get when you bring 220 into the house are
>>>> >two-out-of-possible-three phases. They are, in fact, 120 degrees out of
>>>> >phase.
>>>> Snip
>
>What you aren't considering is that each leg of even a 3-phase system has a
>full sine wave.  Therfore, a center tapped transformer from any single leg of
>a 3-phase system would produce two complete sine waves that were 180 degrees
>out of synch with each other.

True.

>The domestic 220 we find in our homes is just that.  

Nope.  You're forgetting voltage.  If domestic 240V service was simply
two legs of a 240V three phase circuit, then the voltage measured from
leg to leg would be 208V, _not_ 240V.

Certainly, they can make three phase transformers that generate 240V
leg-to-leg, and use two legs for each house.  But, if you look you'll
notice that most pole transformers have only two supply lines, not three.

And of course, if you look around enough, you'll find that many appliances
are rated to go on 208V as well as 240V.  Like many water heaters.
But residential power is almost always 240V.
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