The principle of electrical energy measurement is to detect the actual current, the actual voltage and the phase shift (power factor). This values are giving us the instantaneous power . The power multiplied by the time is the consumed energy.
Let’s take a look at a terminal block for a direct connected threephase 4 wire meter.
The red arrows are indicating the so-called “I-P links”, one for each phase. By unfastening the two screws the link can be moved to the right side. So there will be no connection between the current- and voltage measurement circuits. This links are only for meter testing purpose with a test bench, as here the voltages and currents are provided individually. (The voltages are connected to the screw on the right side of the link.)
A meter in the field must have all links closed.