I am currently looking at this inexpensive power meter modules with TTL interface.
It seems to use internally the same ASIC as many chinese wall-wart power meters: It comes with a current transformer for measuring the current through a live wire and has connections for sampling the voltage on the wire.
My question now is this: Assuming I have a 3-phase AC setup, can I thread all three live phases (i.e. shifted 120° relative to each other) through the current transformer to measure the sum of the POWER in all three phases?
My hunch is that this will not work. My primary concern is that the voltage on only a single phase will be sampled while the current transformer sees the current on three phases which will make calculating the power difficult. Also I believe on AC the direction of the current in the three phases will generally not be aligned leading to cancellations.
Is this correct?
Edit 1: Clarification. I am not attempting to measure a 3-phase load but multiple single-phase loads attached to the three phases. The return current goes through neutral.