Can measuring 50Hz / 60Hz 12V~50Hz/60Hz 380V AC voltage (average); RC Step-down power supply can connect zero line and fire line directly no extra power needed; Anti flash touch design; LED working current should be controlled in 20mA which can lengthen LED life time; Working voltage AC 12V AC 380V accuracy / error 1% Mounting-hole size: 45.5 x 2.5mm; Measuring rate: >/= 200ms/ times 0.6" 3-digit tube; Application range: AC 220V voltage measuring; 22V motor voltage monitor; Inverter output of electricity monitoring and other Ac circuit voltage test; Please note: adopt resistance-capacitance step-down power supply no isolation high voltage require professional electrician to install