GFI stands for "ground fault interrupter." A GFI is required on electrical outlets where there are risks of shock or electrocution. GFIs are used on electrical outlets in kitchens, bathrooms, near swimming pools and for some outdoor electrical outlets. They are also used on extension cords.
GFIs operate by detecting a difference in the current between the "hot" wire--the wire that provides the current, and the neutral or ground wire, through which the current is supposed to return. If the circuit is leaking, the current will be higher in the hot wire than in the ground wire. A leaking circuit is a sign of a short circuit, or possibly someone getting shocked or electrocuted. GFIs are also sometimes referred to as GFCIs, or ground-fault current interrupters.
A circuit breaker is meant to shut down an electrical line when about 20 amperes (amps) goes missing. However, this is much more current than necessary to kill a person or pet. About 0.1 to 0.2 amps (100 to 200 milliamps) are considered lethal, and cause heart fibrillation and cessation of breathing. It is obvious a circuit breaker will not trip in time to save your life if you are being electrocuted. Here is where GFIs come in: they are designed to break the electrical circuit when only 5 milliamps are detected to be leaking.
Ground fault interrupters are designed to respond to current leaks within milliseconds. They have a test button that allows you to determine if the GFI is operating correctly. When the test button is pushed, a small amount of current is diverted from the hot wire through a resistor, causing a current "leak" of about 8 to 10 milliamps. This should trip the circuit, and the "reset" button will pop out. To reset the circuit and the GFI, press the "reset" button back in.
Ground fault interrupters are being used more extensively in industry at the request of the Occupational Health and Safety Administration (OSHA). In addition, the National Electrical Code (NEC) requires GFIs in all kitchens, bathrooms, and wet sinks. They are required in outdoor public areas and around swimming pools and hot tubs. In industry they are required in elevator pits and machinery rooms. Hospital critical care and electrical life support equipment areas must have GFIs. In addition, snow melting equipment and roof-mounted photovoltaic solar panel systems require GFIs.
GFI is also the stock ticker abbreviation for Gold Fields Limited, a South African mining company with over 80 million ounces of gold in reserve. GFI is a software company that provides security for web, email and other computer functions. The GFI group is a wholesale brokerage and trading support company. GFI Capital Resources Group, Inc. is a financial services provider. GFI Genfare is a maker of bus fare collection systems. There are numerous other companies and websites that use GFI in their name.