On 1/12/2011 10:21 PM, wrote:
On Wed, 12 Jan 2011 20:54:48 -0600, Dean Hoffman
wrote:

Metspitzer wrote:

It is considered single phase. If you remove the center tap, you have
the same thing on the primary as you do on the secondary.

If you chose to put the secondary tap anywhere but the center, you
still have 240 total, but the fraction of 240 changes as you move the
center tap.

This sentence is the one that doesn't ring true.
"The two insulated wires each carry 120 volts, but they are 180
degrees out of phase so the difference between them is 240 volts. "


There is NO PHASE DIFFERENCE on a center tapped transformer. If the
voltages were 180 degrees out, there would be 120 on each side and
ZERO voltage across the pair.

I don't think you mean that. Or you have a reference different than
the center tap.

If they were in phase (relative to the tap), they would read 0. Same
as reading between two breakers on the same phase in a breaker box. It's
the same voltage, same phase hence no difference. But of course, it
isn't that way.

Put another way: When current is flowing out the top leg of the
transformer, it is flowing in the bottom leg. Opposite polarity, 180
out of phase.

I'm assuming that was just a quickie mistake and we won't be arguing
this, at least I won't be. I just wanted to correct the record for
anyone else.

For others, 240 center tapped is exactly how two 120 phases are
delivered into the home:

http://www.energyquest.ca.gov/how_it...ansformer.html

Jeff