This instrument is only suitable for pure AC 50-60HZ mains power supply. It cannot be used for square wave, inverter output, and sine wave circuits with modified sine waves, otherwise the instrument be permanently damaged! The digital AC voltage, current and frequency are displayed on the same meter at the same time. The meter does not need to add power supply and transformer. The meter comes with a 120A small transformer. 120A transformer (hole diameter 15mm) can meet standard 21-25 square millimeter standard copper wire through., Weight: 0.22487150724 pounds, Manufacturer: NONDK