Engineering Dictionary of Electronic Terms
"A" "B" "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M",
"N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"

Ground Fault Interrupter

Ground Fault Interrupter. [GFI] A protective device that detects abnormal current flowing to ground and then interrupts the circuit [Live to GND]. A GFI may also be called Ground Fault Circuit Interrupter [GFCI]

A circuit below shows a differential transformer which continuously monitors the circuit to ensure that all the current that flows out to the load [a motor in this case] returns to the source via the circuit conductors. If any leaks to a fault, the sensing circuit opens the circuit breaker and stops the current flow.

In this example the sensing circuit detects the 1 amp difference between the current going out to the load and returning, tripping the GFCI.

GFI Circuit Schematic
GFCI Circuit

GFI Outlet Receptacle

GFI Duplex Outlet
test and reset buttons

GFCIs detect any difference in current between the two circuit wires (the black wires and white wires). This difference in current could happen when electrical equipment is not working correctly, causing leakage current. If leakage current (a ground fault) is detected in a GFCI-protected circuit, the GFCI switches off the current in the circuit, protecting you from a dangerous shock.

GFCIs are set at about 5 mA and are designed to protect workers from electrocution. GFCIs are able to detect the loss of current resulting from leakage through a person who is beginning to be shocked. If this situation occurs, the GFCI switches off the current in the circuit. GFCIs are different from circuit breakers because they detect leakage currents rather than overloads. The example to the right shows a heavy duty extension code fitted with a GFI circuit. Or perhaps a Portable GFCI Outlet fitted to a cord.

Portable GFCI Outlet
Portable GFCI Outlet

In homes built to comply with the National Electrical Code (the Code), GFCI protection is required for most outdoor receptacles (since 1973), bathroom receptacle circuits (since 1975), garage wall outlets (since 1978), kitchen receptacles (since 1987), and all receptacles in crawl spaces and unfinished basements (since 1990).

PC motherboard

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