What is a GFCI?
What is a GFCI?
A Ground Fault Circuit Interrupter (GFCI) is a device to protect against electric shock should someone come in contact with a live wire and a path to ground. The GFCI senses the difference between the currents in the Hot and Neutral conductors. Under normal conditions, these should be equal. However, if someone touches the Hot and a Ground, such as a plumbing fixture or they are standing in water, these currents will not be equal. This might occur if a short circuit developed inside an ungrounded appliance or if someone was working on a live circuit and accidentally touched a live wire.
The GFCI will trip in a fraction of a second at currents well below those that are considered dangerous. Note that a GFCI is NOT a substitute for a fuse or circuit breaker as these devices are still required to protect equipment and property from overloads or short circuits that can result in fire or other damage.
GFCIs can be installed in place of ordinary outlets in which case they protect that outlet as well as any downstream from it. There are also GFCIs that install in the main service panel.
Many GFCIs also test for a grounded neutral condition where a low resistance path exists downstream between the N and G conductors. If such a situation exists, the GFCI will trip immediately when power is applied even with nothing connected to the protected outlets.
How does a GFCI work:
GFCIs typically test for the following condition:
• A Hot to Ground (safety/earth) fault. Current flows from the Hot wire to Ground bypassing the Neutral. This is the test that is most critical for safety.
• A Grounded Neutral fault. Due to miswiring or a short circuit, the N and G wires are connected by a low resistance path downstream of the GFCI. In this case, the GFCI will trip as soon as power is applied even if nothing is connected to its protected (load) circuit.
A Ground Fault Circuit Interrupter (GFCI) is a device to protect against electric shock should someone come in contact with a live wire and a path to ground. The GFCI senses the difference between the currents in the Hot and Neutral conductors. Under normal conditions, these should be equal. However, if someone touches the Hot and a Ground, such as a plumbing fixture or they are standing in water, these currents will not be equal. This might occur if a short circuit developed inside an ungrounded appliance or if someone was working on a live circuit and accidentally touched a live wire.
The GFCI will trip in a fraction of a second at currents well below those that are considered dangerous. Note that a GFCI is NOT a substitute for a fuse or circuit breaker as these devices are still required to protect equipment and property from overloads or short circuits that can result in fire or other damage.
GFCIs can be installed in place of ordinary outlets in which case they protect that outlet as well as any downstream from it. There are also GFCIs that install in the main service panel.
Many GFCIs also test for a grounded neutral condition where a low resistance path exists downstream between the N and G conductors. If such a situation exists, the GFCI will trip immediately when power is applied even with nothing connected to the protected outlets.
How does a GFCI work:
GFCIs typically test for the following condition:
• A Hot to Ground (safety/earth) fault. Current flows from the Hot wire to Ground bypassing the Neutral. This is the test that is most critical for safety.
• A Grounded Neutral fault. Due to miswiring or a short circuit, the N and G wires are connected by a low resistance path downstream of the GFCI. In this case, the GFCI will trip as soon as power is applied even if nothing is connected to its protected (load) circuit.
Why a GFCI should not be used with major appliances:
A Ground Fault Circuit Interrupter is supposed to be a valuable safety device. Why not use them everywhere, even on large appliances with 3 wire plugs?
• A properly grounded 3 prong outlet provides protection for both people and the appliance should a short circuit develop between a live wire and the cabinet.
• Highly inductive loads like large motors or even fluorescent lamps or fixtures on the same circuit can cause nuisance tripping of GFCIs which needless to say is not desirable for something like a refrigerator.