The Triplett ET100 is a useful and necessary tool for residential and commercial electricians, home inspectors, and DIYs, you can detect faulty wiring in 3-wire receptacles. Lights display 5 wiring faults: Open Ground, Open Neutral, Hot/Ground Reverse, Open Hot, Hot/Neutral Reverse with an easy to read fault label on both sides for receptacles with ground up or ground down installation. At the push of a button you can test GFCIs for proper operation. Unique “Loop Design” allows for easier “pulling” removal when testing is complete. cULus Listed.