What is a GFCI receptacle and how to test it...

Often times during an inspection I find a failed or mis-wired GFCI receptacle (outlet) in a home. After getting asked many times "What are they?" and "what do they do?" I figured id share some info for anyone curious about these devices you likely have in your own home. If you don't have any GFCI receptacles in your home, this may encourage you to have them installed.

What is a GFCI?

A GFCI (Ground Fault Circuit Interrupter) is a device commonly used in electrical wiring to disconnect a circuit when unbalanced current is detected between an energized conductor and neutral return conductor. Basically, it helps reduce the risk of electrical shock.

How to test a GFCI receptacle

To test the receptacle GFCI, first plug a nightlight or lamp into the outlet. The light should be on. Then press the "TEST" button on the GFCI. The "RESET" button should pop out, and the light should turn off.

If the "RESET" button pops out but the light does not turn off, the GFCI has been improperly wired. Contact an electrician to correct the wiring errors.

If the "RESET" button does not pop out, the GFCI is defective and should be replaced.
If the GFCI is functioning properly and the lamp turns off, press the "RESET" button to restore power to the outlet.

History

The first high-sensitivity system for detecting current leaking to ground was developed by Henri Rubin in 1955 for use in South African mines.  This cold-cathode system had a tripping sensitivity of 250 mA (milliamperes), and was soon followed by an upgraded design that allowed for adjustable trip-sensitivity from 12.5 to 17.5 mA.  The extremely rapid tripping after earth leakage-detection caused the circuit to de-energize before electric shock could drive a person's heart into ventricular fibrillation, which is usually the specific cause of death attributed to electric shock. Charles Dalziel first developed a transistorized version of the ground-fault circuit interrupter in 1961.  Through the 1970s, most GFCIs were of the circuit-breaker type.  This version of the GFCI was prone to frequent false trips due to poor alternating-current characteristics of 120-volt insulations.  Especially in circuits with long cable runs, current leaking along the conductors’ insulation could be high enough that breakers tended to trip at the slightest imbalance. 
 
Since the early 1980s, ground-fault circuit interrupters have been built into outlet receptacles, and advances in design in both receptacle and breaker types have improved reliability while reducing instances of "false trips," known as nuisance-tripping.

NEC Requirements for GFCI's

The National Electrical Code (NEC) has included recommendations and requirements for GFCIs in some form since 1968, when it first allowed for GFCIs as a method of protection for underwater swimming pool lights.  Throughout the 1970s, GFCI installation requirements were gradually added for 120-volt receptacles in areas prone to possible water contact, including bathrooms, garages, and any receptacles located outdoors. The 1980s saw additional requirements implemented.  During this period, kitchens and basements were added as areas that were required to have GFCIs, as well as boat houses, commercial garages, and indoor pools and spas.  New requirements during the '90s included crawlspaces, wet bars and rooftops.  Elevator machine rooms, car tops and pits were also included at this time.  In 1996, GFCIs were mandated for all temporary wiring for construction, remodeling, maintenance, repair, demolition and similar activities and, in 1999, the NEC extended GFCI requirements to carnivals, circuses and fairs. The 2008 NEC contains additional updates relevant to GFCI use, as well as some exceptions for certain areas.