The Triplett ET100 GFCI Outlet / Receptacle Tester is a useful and necessary tool for residential and commercial electricians, home inspectors, and Dyers, allowing you to detect faulty wiring in 3-wire receptacles. Built-in lights display 5 wiring faults including Open Ground, Open Neutral, Hot/Ground Reverse, Open Hot, and Hot/Neutral Reverse. The unit also features an easy-to-read fault label on each side, useful for receptacles with ground up or ground down installation. With just the push of a button you can test GFCIs for proper operation. Plus, the unique "Loop Design" allows for easier removal when testing is complete. callus Listed.