PCE Instruments PCE-360-ICA Instruction Manual page 39

User Manual
 Press  key to exit the energy measurement.
P
Q S
U1 U2
※ U1 must be connected to voltage source during the measurement of U2, U3, I1, I2
and I3, because U1 is the main signal source of the whole meter measuring system.
Otherwise you could not have any measurement from U2, U3, I1, I2 and I3.