There is a circuit breaker in every home, which trips the switch if there is a fault somewhere in a circuit.

And there is a GFCI outlet/switch which also trips if there is a fault downstream.

If circuit breaker is there, then why do we need GFCI ? May be dumb question but I am dumb when it comes to electricity.

  • A GFCI means the difference between going to hospital or funeral home. A GFCI protects when current that can kill goes to wrong place, housing of a fridge. A circuit breaker only protects from over current in circuit/wires, does not protect if you are part of circuit.
    – crip659
    May 12 at 12:50
  • 1
    What's happening here is you don't know anything about electricity. So you're assuming all faults are the same thing. They're not. There's more to it than that. Now, there's a paper by Dunning and Kruger that you ought to read, which talks about the difference between "being dumb and thinking you know stuff" vs "being dumb and knowing you actually don't know stuff". The former is sad... the latter is real power. Because that, you can fix. May 12 at 18:02

Circuit breakers trip on overcurrent, including too many devices. A low level fault to ground may not pass enough current to trip a regular circuit breaker.

A GFCI device compares the current on the hot and neutral, if not equal it breaks the circuit. It does this by running both wires through the same current transformer (donut), if the current is equal the magnetic fields cancel each other, and no current is detected by the current transformer. Current flowing a 150% of circuit breaker rating should trip the circuit breaker, but if the outgoing and returning current were the same no magnetic field would be detected by the current transformer and the GFCI would not trip.

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