Klein Tools receptacle testers are designed to detect the most common wiring problems in standard and GFCI receptacles. A convenient chart on the tester helps determine wiring condition in outlet, based on LED lights results. Conditions indicated open ground, reverse polarity, open hot, open neutral, hot/ground reversed. Conforms to UL standard 1436, Certified to CSA standard C22.2 160Built to withstand a 6.6 feet (2 m) dropOperating temp 32 degree Fahrenheit to 140 degree Fahrenheit (0 degree Celsius to 40 degree Celsius)Works on GFI outlets and confirms operation of the ground faultNominal voltage 110/125 volt AC at 50/60 hertz in 3-wire outletDetects the most common wiring problems in standard and GFCI receptacles