GFCI (Ground Fault Circuit Interrupter) protection is a system that shuts down the protected electric circuit -- opens it -- when it senses an unexpected loss of power, presumably to ground. GFCI protection devices constantly monitor and compare the amount of power flowing from the panel on the hot or phase wire and the amount returning on the neutral wire. Any time the returning power drops even slightly below the amount being supplied, the protection device will trip and open the circuit.
GFCI devices, including receptacles and circuit breakers, work by passing both the hot wire and the neutral wire through a sensor - such as a differential transformer - and connecting the sensor to a solenoid or relay that opens switch contacts built into the the power conductors inside the device -- in front of the transformer, of course. The schematic above (or in a [You may have noticed that the working parts of a GFCI system don't include the circuit ground wire or the ground slot on a receptacle. That's because GFCIs are designed to protect us against a ground fault, which is an unintended loss of power to ground -- possibly through a person. The regular grounding system protects the equipment that is attached (or plugged in) to the circuit against a ground fault in it. GFCI devices are designed to protect people, not equipment.
When it is working properly, a GFCI - or GFI - device will open its protected circuit when the difference between the current coming in and the current going out reaches .005 ampere. That's 5 milliamp, an amount most of us can't even sense. Making sure it is working properly is the reason for testing it once a month. Note: sometimes GFCI is called GFI
GFCI devices, including receptacles and circuit breakers, work by passing both the hot wire and the neutral wire through a sensor - such as a differential transformer - and connecting the sensor to a solenoid or relay that opens switch contacts built into the the power conductors inside the device -- in front of the transformer, of course. The schematic above (or in a [You may have noticed that the working parts of a GFCI system don't include the circuit ground wire or the ground slot on a receptacle. That's because GFCIs are designed to protect us against a ground fault, which is an unintended loss of power to ground -- possibly through a person. The regular grounding system protects the equipment that is attached (or plugged in) to the circuit against a ground fault in it. GFCI devices are designed to protect people, not equipment.
When it is working properly, a GFCI - or GFI - device will open its protected circuit when the difference between the current coming in and the current going out reaches .005 ampere. That's 5 milliamp, an amount most of us can't even sense. Making sure it is working properly is the reason for testing it once a month. Note: sometimes GFCI is called GFI
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