CORRECT PHASE MATCHING BETWEEN CHANNELS
Phase matching of the system is another critical issue.
The errors induced in the system at PF = 1 are minimal.
A power factor of 0.5 with a phase error as little as
0.5 degrees will cause a 1.5% error in the power mea-
surement.
according to "AN-564 APPLICATION NOTE" from AD.
Put your transformer to rest, go with optical:
http://coolarduino.wordpress.com/2013/02/27/power-energy-meter-phase-power-and-energy/