GW INSTEK GPT-9901A AC Withstanding Voltage Tester Safety Hi-PotGW Instek GPT 9901A AC Withstanding Voltage Tester (Hi Pot Safety Tester) The GW Instek GPT 9901A is an AC withstanding voltage tester designed for electrical safety compliance testing. Commonly referred to as a Hi Pot tester, it evaluates the insulation strength of electronic components, equipment, and systems by applying high voltage to ensure compliance with international safety standards. Its user friendly interface, programmable test settings,