A GFCI, or ground fault circuit interrupter, offers protection against severe or fatal electric shocks and prevents electrical fires by detecting ground faults. Installation of the device could prevent thousands of injuries each year due to burn and electric shock. The GFCI constantly monitors electricity flowing in a circuit. If the current flowing differs by a small amount upon returning, the GFCI quickly switches off power to the circuit. Although you may still receive a shock, you should not receive a serious injury.
Switch the breaker to the circuit off at the main service panel.
Remove the old outlet from the wall box and remove the wires from the terminals. If there are two or more electrical cables coming into the wall box, separate the wires according to which one provides incoming power from the main service panel and which one carries power downstream to additional receptacles.
Connect the black wire of the incoming power cable to the "Line" terminal marked "Black" on the GFCI receptacle.
Connect the white wire of the incoming power cable to the "Line" terminal marked "White" on the GFCI receptacle.
Connect the green or bare wire to the green screw on the GFCI receptacle.
Connect the black and white wires of the second cable (if applicable) to the "Load" terminals on the GFCI receptacle.
Fold the wires neatly and push them into the wall box.
Screw the receptacle into place and attach a cover.
Switch the breaker on at the main service panel.
Plug in a radio and test your installation by pressing the receptacle's "Test" button. The radio should turn off.
Press the "Reset" button and the power should turn back on.