... . Can test the three~phase AC voltage, current, phase between voltage, phase between current, phase between voltage¤t, frequency, phase, active power, ... CT of the differential protection system, check if the ammeter is wiring correctly, check the circuit and equipment. ... error ±3° under working (phase error ±5° if current amplitude under 10mA). Best Voltage Meter, Handheld Three-Phase Meter DF-300V