Question: how does a gfci work?
Answer: Unlike a home's fuse, the GFCI is integrated in the outlet itself. ... A GFCI monitors the amount of current flowing from hot to neutral. If there is any imbalance, it trips the circuit. The GFCI senses a mismatch as small as 4 or 5 milliamps, and it can react as quickly as one-thirtieth of a second.