I think if I understand it, if you use both phases of power at home then if you cross the hots you can produce 240volts.
06-21-13:
Coxhaus,
A little background.
Most homes in housing developments in the US are fed from a single phase transformer. The 240V nominal secondary winding has a center tap, CT, midpoint of the winding. The CT is called the neutral.
The secondary winding is called a split phase winding.
The neutral is intentionally connected to earth at the main electrical service of the house. The neutral then becomes the Grounded Conductor.
The other two conductors are called the Ungrounded Conductors. Also referred to as the Hot conductors.
From Hot to Hot conductor there is a difference of potential, voltage, of 240V nominal. From either Hot conductor to the neutral conductor there will be 120V, nominal.
Thus a 120/240Vac grounded 3 wire single phase power system.
Click on single phase power systems.
http://openbookproject.net/electricCircuits/AC/AC_10.html#xtocid174140
I would think anybody who uses 220 power conditioning is subject to this and anybody who uses multiple plugs from different phases are all in the same boat.
If you would take the time and research the archives of audio forums you will find the vast majority of audiophiles when feeding their audio equipment from two or more 120V branch circuits will feed the circuits from branch circuit breakers that are fed from the same Line in the electrical panel, when the equipment is connected together by ICs. All from Line one (L1) or all from Line two (L2) but not from both.
As for your 3 isolation transformers you have the same situation. It doesn't matter whether you fed the xfmrs with 240V or 120V. (240V is best IMO). Two of the 3 will be in phase with one another. The other has a 50/50 chance of being in phase with the other two. My simple test, in one of my previous posts above, will tell you for sure.
IF one of the xfmrs is out of phase with the other two all that needs to be done is to reverse the two primary hot branch circuit wires at the breaker that feeds that xfmr.
Transformer phasing?
Click on phasing.
http://openbookproject.net/electricCircuits/AC/AC_9.html#xtocid174063
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