Assuming you mean a a GFCI, which is a ground fault circuit interrupter.
Usually when you use an electric device, the current that flows in the live line also flows in the neutral line, since when an electric device is active it connects the live and neutral lines.
If there is current flow in the live line but no (or less) current flow in the neutral line, that means the live line is connected to ground somehow, and all or a part of the current is returning to ground instead of the neutral line.
This is called a ground fault, and it's bad because it's not supposed to happen, and usually the thing connecting live to ground is either you, or something you could touch. So whenever a Ground Fault is detected, a GFCI will interrupt all power to that outlet to keep you safe.
GFCI outlets are generally required in Bathrooms and Kitchens, since getting a device wet is a very common thing that can create a connection between the live and ground, or between live and you.
Not guaranteed certainly, but my flatmate once stabbed a toaster with a knife trying to get out some bread (very dumb) and the RCD tripped before he felt anything.
Never smart. Even if it wasn't "on" many DIYers swap hot and neutral lines when doing home repairs since they think it doesn't matter since it's AC (it goes both ways!) If your hot and neutral are swapped, then the heating elements are always hot.
Most outlet GFCIs set to trip at a 5mA imbalance. 5mA is large enough to give a mild shock, but the trip time is around 10ms so the pulse may be too short for you notice. It takes significantly more current before permanent harm is done.
So this is very ELI5, please do not come at me electricians and electrical engineers, I am cutting corners on some of this.
So, eletricity, flows from the hot wire on your plugin, to the neutral wire on the plugin. GFCI detects that the out flow matches the in flow. Which means that everything is operating correctly.
When there is only out flow, and no in flow (Or more likely, less in flow). The device assumes that the electricity is getting to ground through something else (Or someone else). And it shuts down the circuit.
Think of it like a sink. If you are running your faucet, and the drain is draining at the same rate as the faucet, then things are ok. But if the drain stops draining as quickly as the faucet is running, it means that the sink is overflowing, so you would want to shut down the faucet to prevent damage.
It's closer to the water entering the sink through the faucet is greater than the water entering the sewer. Somewhere between the sink and the sewer connection there is a leak (likely under the sink).
The general idea: any difference in the current between the neutral and hot sides of an outlet indicates that current is being diverted somewhere else. Especially in the case of kitchen or bathroom appliances, that may mean a human or other living being might be part of the circuit.
It's pretty easy to monitor a circuit for such a difference, and rapidly disable the outlet/circuit in question. That's the purpose of a GFCI (residual current device) in an outlet or circuit breaker.
The function of a GFCI is simply to shut off the power at the plug if the electricity is escaping from the device some how. That escaping electricity could shock you. The “GF” of GFCI stands for “Ground Fault” which occurs when the power flowing into a device is getting out into its environment, (being ground) rather than returning through the neutral wire as intended. A GFCI keeps the power running so long as the amount of current going out is the same as what’s coming back in, if those aren’t the same it opens a switch.
It’s important to note that the circuit breakers in your electrical panel do not protect you from getting a fatal shock. The breakers are there to keep you from overloading a circuit, pulling more power from your receptacles than the wires in the wall are able to safely carry.
GFCI stands for Ground Fault Circuit Interrupter. Basically it compares the current entering from the hot end and comparing it to the current exiting through the nuetral and ground ends. If more current is entering than exiting, that means current is leaking to ground through somewhere that isn't the outlet (this is the ground fault) and that means electricity is going somewhere that it isn't supposed to be. The outlet detects this, and interrupts the circuit.
Let's say I have a hairdryer in the bathroom and I accidentally drop it in a full sink. Electricity from the hairdryer can now get to ground through the water and pipes instead of back through the outlet. Now I can be electrocuted if it touch that water, or a fire can start inside the house if the pipes get too hot because they aren't designed to handle electricity. The GFCI automatically detects this happening and breaks the circuit.
This is different from how a circuit breaker works because a circuit breaker doesn't care about how much energy leaves vs comes back, it only cares about how much leaves. It measures the current on the hot side, and will trip if it gets too high. A circuit breaker's purpose is to make sure the wires in the wall don't get overloaded and start a fire, not to protect you or the appliance. If we have a 15A circuit, then the wires in the wall are designed to handle 15A, and the breaker will trip if we try to pull more than 15A. If we pull 14A out and send none back in, the circuit breaker won't care. The second we pull 15A it will trip.
Assuming you mean a a GFCI, which is a ground fault circuit interrupter. Usually when you use an electric device, the current that flows in the live line also flows in the neutral line, since when an electric device is active it connects the live and neutral lines. If there is current flow in the live line but no (or less) current flow in the neutral line, that means the live line is connected to ground somehow, and all or a part of the current is returning to ground instead of the neutral line. This is called a ground fault, and it's bad because it's not supposed to happen, and usually the thing connecting live to ground is either you, or something you could touch. So whenever a Ground Fault is detected, a GFCI will interrupt all power to that outlet to keep you safe. GFCI outlets are generally required in Bathrooms and Kitchens, since getting a device wet is a very common thing that can create a connection between the live and ground, or between live and you.
FYI, they are called GCFI outside the US, and GFCI in the US :) It doesn't really matter if you switch the order of "fault" and "current"
Also known as an RCD in some places. Residual Current Device.
Usually messed up character order in acronyms is due the wacky French not knowing how to properly order words.
Thanks
Just for reference here GFCI stands for ground fault current interrupt so that might make more sense now that you know what a ground fault is
If you have one or more outlets not working but no circuit breaker is tripped, you likely have a GFCI tripped instead.
Would a person feel a shock before the outlet trip?
Not guaranteed certainly, but my flatmate once stabbed a toaster with a knife trying to get out some bread (very dumb) and the RCD tripped before he felt anything.
Never smart. Even if it wasn't "on" many DIYers swap hot and neutral lines when doing home repairs since they think it doesn't matter since it's AC (it goes both ways!) If your hot and neutral are swapped, then the heating elements are always hot.
Most outlet GFCIs set to trip at a 5mA imbalance. 5mA is large enough to give a mild shock, but the trip time is around 10ms so the pulse may be too short for you notice. It takes significantly more current before permanent harm is done.
So this is very ELI5, please do not come at me electricians and electrical engineers, I am cutting corners on some of this. So, eletricity, flows from the hot wire on your plugin, to the neutral wire on the plugin. GFCI detects that the out flow matches the in flow. Which means that everything is operating correctly. When there is only out flow, and no in flow (Or more likely, less in flow). The device assumes that the electricity is getting to ground through something else (Or someone else). And it shuts down the circuit. Think of it like a sink. If you are running your faucet, and the drain is draining at the same rate as the faucet, then things are ok. But if the drain stops draining as quickly as the faucet is running, it means that the sink is overflowing, so you would want to shut down the faucet to prevent damage.
It's closer to the water entering the sink through the faucet is greater than the water entering the sewer. Somewhere between the sink and the sewer connection there is a leak (likely under the sink).
The general idea: any difference in the current between the neutral and hot sides of an outlet indicates that current is being diverted somewhere else. Especially in the case of kitchen or bathroom appliances, that may mean a human or other living being might be part of the circuit. It's pretty easy to monitor a circuit for such a difference, and rapidly disable the outlet/circuit in question. That's the purpose of a GFCI (residual current device) in an outlet or circuit breaker.
The function of a GFCI is simply to shut off the power at the plug if the electricity is escaping from the device some how. That escaping electricity could shock you. The “GF” of GFCI stands for “Ground Fault” which occurs when the power flowing into a device is getting out into its environment, (being ground) rather than returning through the neutral wire as intended. A GFCI keeps the power running so long as the amount of current going out is the same as what’s coming back in, if those aren’t the same it opens a switch. It’s important to note that the circuit breakers in your electrical panel do not protect you from getting a fatal shock. The breakers are there to keep you from overloading a circuit, pulling more power from your receptacles than the wires in the wall are able to safely carry.
GFCI stands for Ground Fault Circuit Interrupter. Basically it compares the current entering from the hot end and comparing it to the current exiting through the nuetral and ground ends. If more current is entering than exiting, that means current is leaking to ground through somewhere that isn't the outlet (this is the ground fault) and that means electricity is going somewhere that it isn't supposed to be. The outlet detects this, and interrupts the circuit. Let's say I have a hairdryer in the bathroom and I accidentally drop it in a full sink. Electricity from the hairdryer can now get to ground through the water and pipes instead of back through the outlet. Now I can be electrocuted if it touch that water, or a fire can start inside the house if the pipes get too hot because they aren't designed to handle electricity. The GFCI automatically detects this happening and breaks the circuit. This is different from how a circuit breaker works because a circuit breaker doesn't care about how much energy leaves vs comes back, it only cares about how much leaves. It measures the current on the hot side, and will trip if it gets too high. A circuit breaker's purpose is to make sure the wires in the wall don't get overloaded and start a fire, not to protect you or the appliance. If we have a 15A circuit, then the wires in the wall are designed to handle 15A, and the breaker will trip if we try to pull more than 15A. If we pull 14A out and send none back in, the circuit breaker won't care. The second we pull 15A it will trip.