You really need to measure (connect) voltage. Voltage variation, wave shape, reactive loads will all affect the measurement. You cannot just multiply current by an assumed voltage.
Well, you can, it's just a matter of how much error you are willing to accept.
Our mains voltage for example doesn't vary by a huge amount, so multiple a fixed value by the RMS current and you are in the ballpark.
But that will only give you apparent power, not true power. If you could obtain the phase of the sine wave by capacitive coupling, then you stand more of a chance.
With capacitive coupling you may stand a chance but the phase shift introduced by the coupling may only be calibrated out if it is the coupling is 100% repeatable.
Which it's not.
Providing the resistive element dominates, then the error will be minimal. For example, if the meter's input impedance is 100M and the capacitance to the mains conductor is 100pF (31M8, at 50Hz) then the phase shit will be minimal.
Shielding and filtering to remove high frequency interference will be more of a challenge, than phase shift.
You really need to measure (connect) voltage. Voltage variation, wave shape, reactive loads will all affect the measurement. You cannot just multiply current by an assumed voltage.
Well, you can, it's just a matter of how much error you are willing to accept.
Our mains voltage for example doesn't vary by a huge amount, so multiple a fixed value by the RMS current and you are in the ballpark.
But that will only give you apparent power, not true power. If you could obtain the phase of the sine wave by capacitive coupling, then you stand more of a chance.
With capacitive coupling you may stand a chance but the phase shift introduced by the coupling may only be calibrated out if it is the coupling is 100% repeatable.
Which it's not.
Providing the resistive element dominates, then the error will be minimal. For example, if the meter's input impedance is 100M and the capacitance to the mains conductor is 100pF (31M8, at 50Hz) then the phase shit will be minimal.
Shielding and filtering to remove high frequency interference will be more of a challenge, than phase shift.
ot: congrats on your 11999 post!

I think 100pf is to ambitious, according to my "back on the envelope" calculations with a probe length limit of 50mm (for practical reasons) and dual insulation (required by law) and 2,5mm2 cable the coupled capacitance is max. 10pf.
And then there are repeat-ability issues because of physical probe placement, different wire types and insulation material and thicknesses.
In a controlled (lab) environment something like this maybe doable with usable accuracy (say below 5% error) but
the probe must be calibrated in place and not be touched after.
Sounds like a nice topic for a video to me, including some experiments etc.
