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.PRODUCT FEATURES:• Conforms to UL Std 1436, Certified to CSA Std C22.2 #160.• Built to withstand a 6.6 ft. (2m) drop.• Operating temp: 32°F to 140°F (0°C to 40°C).• Works on GFI outlets and confirms operation of the ground fault.• Nominal Voltage: 110/125V AC at 50/60Hz in 3-wire outlet.