For the 3-phase measurement with closed calibration links, insulated current transformers of the type ZETA ICT-2030 of class 0.01 are used. They are characterized by a high output power and express small magnitude and angle errors in the specified measuring range of 10 mA to 120 A.
Meters with transformer connection or with open calibrations links can also be measured without isolated current transformers. The current transformer is switched on and off automatically within a few seconds via motor control.