MESTEK ST06 is an electrical receptacle tester that tests the wiring conditions at an electrical outlet and inspects GFCI devices. The color LCD displays the voltage, the time required to trip a GFCI device, identifies SEVEN common wiring problems, open ground,open neutral, reversed hot/ground,reversed hot/neutral, wired correctly, open hot, dual open( neutral & ground) . It is designated for use with North American 3-wire 120Volt electrical outlets.