Receptacle testers are used to test wiring in electrical receptacles. They identify outlets that are open ground, open hot or open neutral; hot, hot on neutral, or ground reversed with open hot; and which have faulty wiring or reverse polarity. Receptacle testers can also be used to identify live circuits, determine the ground leg of a two-wire receptacle, and to check three-wire grounding outlets. Most products have a durable, ergonomic plastic case and several neon lamps which indicate the type of reading. Some products that are designed for three-wire, 125 VAC circuits can also be used to test ground fault circuit interrupters (GFCI) for proper operation. GFCI devices are protected circuit breakers that most building codes require in areas which contain water lines. GFCI de-energizes the circuit if an unsafe flow of current to ground is detected.