What is a GFCI Outlet - How does a GFCI Work?
A GFCI (ground fault circuit interrupter) outlet is a device that adds 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.
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 may or may not trip if you receive a shock, but it will not trip fast enough to protect you from harm. A GFCI outlet is more sensitive and acts faster than a circuit breaker or fuse and is more likely to protect you from a deadly shock 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 loads upstream nor downstream on the circuit are protected.
If you have an outlet that doesn't work, and the breaker is not tripped, look for a GFCI outlet which may have tripped. The non-working outlet may be down line from a GFCI outlet. Note that the affected outlets may not be located near the GFCI outlet, they may be several rooms away or even on a different floor.
How To Test a GFCI Outlet
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.