The Klein Tools RT390 Is A Circuit Analyzer That Tests The Wiring Conditions At An Electrical Outlet, Displays Ac Line Voltage, Inspects Afci and Gfci Devices With Time to Trip Device, and Performs Voltage Drop Tests At 12A, 15A and 20A Current Loads. Results Are Easy to Understand With Large, Color LCD. The Tester Is Designed For Use With North American 120V Ac 3-Wire Electrical Outlets.