It does require reference voltages, which are obtained via voltage transformers.
As I recall, iotawatt has 2 modes, one which requires 3 voltage transformers, 1 for each phase which are wired directly into your supply (just like PZEM). The transformers reduce the AC voltage, making it easier (and safer) for iotawatt to analyse.
The second mode uses derived reference by just using 1 transformer on one phase, and then shifting it's phase by 120 and 240 degrees to assimilate the other 2 phases.
This is less accurate.
So the upshot is that it does also require connection to your live wires.
Sorry @craigcurtin but I don't share your enthusiasm for iotawatt 
