Ground Fault Circuit Interrupter (GFCI)
If current leaks through a person’s body, it could cause ventricular fibrillation and electrocution. A GFCI stops current flow in a circuit when it detects leakage current to ground.
A GFCI continuously compares line path current with neutral path return current. If it detects an imbalance, it immediately opens the circuit. Class B GFCI's must trip on greater than 20 mA current within 7 ms. Class A GFCI's must trip on greater than 6 mA current within 6 ms.
GFCI technology can be implemented in either an electrical outlet or in a circuit breaker, and detects leakage down-circuit from the GFCI. GFCI's have been required by the U.S. National Electric Code (NEC) and Canadian Electric Code (CEC) for decades. The most critical locations for GFCI protection are near access to ground or conductive water, such as in the basement, outdoors, in bathrooms and in kitchens.
GFCI's have saved thousands of lives since their introduction. The average number of electrocutions in the United States has dropped from 500 per year before the GFCI to about 150 per year in recent years. This safety device was introduced by The Rucker Company in the late 1960’s. The GFCI technology itself was invented by Dr. Charles Dalzeil of the University of California, Berkeley.
Diagram of a receptacle with GFCI protection: