The "Reset" and "Test" buttons found on some electrical outlets are part of what is known as a ground fault circuit interrupter, or GFCI. They are part of a specially designed circuit that is used to detect an imbalance in current flow between the hot and neutral wires and to cause an interruption of current flow if an imbalance is sensed.
It cannot be over-stated how important it is to properly install and connect electrical wiring. In areas where electrical appliances or tools will be used in close proximity to water--such as bathrooms, kitchens and laundry rooms--a GFCI is installed to provide protection against electric shock. Electric shocks can cause serious harm or even death. The "Test" and "Reset" buttons on these GFCI outlets allow for the safe determining of the proper operation (correct wiring) of these outlets.
The functions of the "Reset" and "Test" buttons on a GFCI wall outlet are to allow testing of the GFCI circuit and ensure its reliability in providing protection from electric shock. Pressing the "Test" button interrupts current to the outlet, and anything plugged into it will lose power. Pressing the "Reset" button restores current flow to the outlet. If pressing "Reset" does not restore power you have either a defective GFCI or a wiring problem. If pressing the "Test" button does not make the "Reset" button pop out, you have a wiring problem that should be immediately corrected.
Like lots of other things, the way that a GFCI operates and the functions of the "Test" and "Reset" buttons can be misunderstood by those not trained in electrical wiring procedures. Unlike circuit-breakers and fuses, which are designed to detect too much current and "trip" or break the circuit, a GFCI is designed to measure the current flowing into a device and compare the current flowing back. A discrepancy as small as 5 mA (UL requirement) will cause a GFCI to interrupt current to the outlet.
When it comes to being able to test a wall outlet for proper and safe operation, the "Test" and "Reset" buttons can save the cost (in many cases significant) associated with calling a licensed electrician to provide service. If a wall outlet equipped with a GFCI circuit does not provide electrical power, it could be because a curious child played with the "Test" or "Reset" buttons. A test using the "Reset" and "Test" buttons will inform an adult that the outlet is functioning properly.
Like oil and water, electricity and water do not mix very well. In areas where electricity is used near water, the inadvertent mixing of the two can be very dangerous and even fatal. Having ground fault circuit interrupter outlets equipped with "Test" and "Reset" buttons greatly improves the margin of safety. Using the "Test" and "Reset" buttons can help determine the status of the outlet and if taking action is necessary.