Hi Augusto,
That does make more sense now, the point here would be to synchronize the actual sample time of the analog to digital converters. In which case a synchronized clock would be needed for all the ADE7878's.
To give you an idea of the maximum delay you would see between systems, the rate at which the RMS register is updated is 8kHz. This means that the maximum delay between RMS readings from 2 different parts would be 125us. Is this not acceptable? Other than that, one way to synchronize the clock of each part would be to use the PPS signal to start an accurate clock for each ADE7878 and this way they would be clocked at the same time. These clocks would have to have precisely the same frequency.
Although it is important to note that reading a single RMS value will have some amount of ripple associated with it and that's why we recommend reading the value as many times as possible over 1 second (reading at least 60 times) and averaging that value to keep it stable. The other possibility is to read it synchronously with the voltage zero-crossings.
Regards,
Dlath