How To Test if a GFCI Outlet is Working
GFCI outlets (ground fault circuit interrupter) are designed to add a greater level of safety by reducing the risk of electric shock. Most building codes now require that a GFCI outlet be used in wet locations such as bathrooms, kitchens, laundry rooms and outdoors.
GFCI outlets should be tested periodically, at least once a year. A GFCI outlet has a "Test" and a "Reset" button. Pressing the "Test" button will trip the outlet and break the circuit. Pressing the "Reset" will restore the circuit. If pressing the test button does not work, then replace the GFCI outlet. If the outlet does pop when you press the "Test" button, but the outlet still has power, the outlet is mis-wired. A mis-wired. outlet is dangerous and it should be fixed immediately.
Some models of GFCI have a status light to indicate whether the outlet has power, some use the indicator light to identify a problem such as being mis-wired. A green light indicates correct wiring and/or the outlet has power. Because there is no standard though, other indicators are open to interpretation depending on brand and year of manufacture.
A GFCI outlet monitors for a current imbalance between the hot and neutral wires and breaks the circuit if that condition occurs. A circuit breaker usually will trip if you receive a shock, but it may not act fast enough to protect you from harm. A GFCI outlet is more sensitive and acts faster than a circuit breaker or fuse and is thus an important safety feature.
A GFCI outlet may be wired in a branch circuit, which means other outlets and electrical devices may share the same circuit and breaker (or fuse). When a properly wired GFCI trips, the other devices down the line from it will also lose power. Note that devices on the circuit that come before the GFCI are NOT protected and are not affected when the GFCI is tripped. If the GFCI outlet is improperly wired, none of the circuit, upstream nor downstream is protected.