GFCI information sheet.

I thought I would put together an information sheet, on the purpose and use of a GFCI.
This device may save you or a family member from a dangerous or fatal shock!

What is a GFCI?
What does a GFCI do for us?
Who needs or should have GFCI's in their houses?

First of all a GFCI is a Ground Fault Circuit Interrupter. It's purpose is to protect people using electrical circuits and appliances.  The GFCI will open the circuit if a current leakage or fault (to ground) exceeds 0.006 A, (6 mA). 
NOTE: A PERSON MAY BE ELECTROCUTED BY AS LITTLE AS ONLY 2 ma.

Normally the current going to the appliance or device along the ungrounded (hot) wire (should be black) and the current returning to the source along the white or grounded neutral conductor are equal. During a ground fault or short circuit (to ground), however, an imbalance occurs and the difference represents a dangerous shock hazard. A GFCI, monitoring the circuit, will sense any imbalance greater than 6 mA and will immediately open the circuit, stopping the dangerous current flow. 
If you find that you have a  GFCI that is tripped, it can be reset by pressing the red button on the receptacle or on the GFCI breaker. 
Your GFCI, whether on the outlet or on the circuit breaker, may be tested by pressing the test button on each unit. If they seem to trip for no apparent reason, have an electrician check out the circuit and find out what is causing the GFCI to activate.

The National Electrical Code requires GFCI protection at the following:
1.   ALL 125 V, single-phase, 15 and 20 A receptacles in bathrooms and outdoors where there is direct grade access. 
2.    At least one identified basement receptacle.
3.    All countertop receptacles within 6 feet of the kitchen sink.
4.    All 125V, single phase, 15 and 20 A receptacles in garages unless:
       a.    Not readily accessible.
       b.    Dedicated for a cord-and-plug-connected fixed appliance.
5.    All 120 V, single-phase, 15 and 20 A receptacles which are not part of permanent wiring (such as those used for temporary power during construction).

These code requirements are not retroactive so you do not have to do this to older houses, but they are required for all new construction.
You can add GFCI protection to your house and it's not difficult to do. They may be installed as breakers or receptacles. The receptacle GFCI units are cheaper and can be installed in the bathroom, kitchen, outdoors, or in a basement. They may be connected so as to protect more than one receptacle on the same circuit. 
DIRECTIONS MUST BE FOLLOWED EXACTLY FOR THE PROTECTION TO WORK AS IT IS SUPPOSED TO, SO IF YOU ARE NOT FAMILIAR WITH ELECTRICAL WIRING, HAVE A LICENSED ELECTRICIAN DO THE WORK FOR YOU.

This information is from MODERN RESIDENTIAL WIRING,  ISBN 0-87006-902-0
Jerry O. Hemby
W1NRA