... the power supply is DC voltage,positive and negative can not be connected wronging,or it will be burn the meter.3 ... ,above 500V should concect the current transformerXXX/100V.4.Frequency meter , sampling AC voltage signal input value,(110V-380V), i.e ... of frequency is 30.0Hz-99.9Hz5.Technical Parameter 1.Power supply: AC220V 2.Accuracy≤input full range of 0.5 ...