What would happen if a "4 wires energy meter" is used with a 3 phase device ?

[tigrou]

I know there is two types of "3 phase energy meter" that exists : 4 wires (3 phases and 1 neutral) and 3 wires.

I'm wondering if watts would still be counted correctly if a 3 phase device (eg: a 3 phase motor) is used on a 4 wires meter (thus ignoring neutral line).
Does it depends if the 3 phases are balanced ?

AFAIK : 4 wires meter get the voltage between each phase and neutral, then "multiply it" by current of each phase.
3 wires meter get the current of two phases only, then multiply by voltage between that phase and the 3rd one (the one for which current is not monitored)

Those schematics might help :

[m k]

Meter doesn't know what it is metering.

Triangle base, there's no potential difference.