A Circuit Breaker
A ground fault circuit interrupter (GFCI), is a type of circuit breaker that shuts off electric power when it detects an imbalance between the outgoing and incoming current. Its purpose is to protect people from an electric shock that happens when current travels through a person’s body due to an electrical fault such as a short circuit, insulation failure, or equipment malfunction. Regular circuit breakers shut off power when the current is too high, like 10, 15, or 20 amps, but just 0.030 amps through a body can stop the human heart. The GFCI breaks the circuit when it detects an imbalance of only 0.005 amps.
A circuit breaker protects the house wires and receptacles from overheating and possible fire. A GFCI protects people and often found in bathrooms, hot tub & pool areas or kitchens where electrical devices are used and people’s bare flesh may be in contact with the floor or metal fixtures which provide an alternate path for current to travel in the case of an electrical fault.
A GFCI can also prevent fires from short circuits and other electrical faults that don’t involve humans such as a low current short where the current never reaches the trigger point for a circuit breaker. (Example: a live wire falls in a tub of water or wet soil and only 1 or 2 amps of current flows).
How GFCI’s Work?
Electrical current from the “Live” side of an outlet, runs through an electrical device, and returns through the “Neutral” side of the outlet. If a person touches a bare “live” wire, current can travel through their body to any other body part connected directly or indirectly to the earth or ground, such as through metal such as plumbing pipes or through moist tiles or a bathtub full of water where the water acts as a conductor. Salty or soapy water increases the conductivity, making salt water pools and hot tubs more dangerous. It only takes so little current to kill a someone, even a poor conductor can result in a lethal shock.
The GFCI device uses a differential transformer to compare the current “going out” on the “live” side with the current “coming back in” on the neutral. If there is a big enough difference between the two, typically 5 milliamps, then that is considered an imbalance, and an internal solenoid mechanically trips the built-in circuit breaker cutting off connection to both the Live and Neutral sides of the outlet.
The assumption is that some of the outgoing current is going through a person or object and is taking an alternate route back to Neutral.
Death caused by electricity (Electrocution) can occur when as little as 30 milliamps of current flows through the heart for just a fraction of a second. A GFCI protects at a level which is much lower than what is needed to cause harm.
If a GFCI device trips and the fault is later fixed, then the user can reset the GFCI device by pushing the reset button. If the problem is not fixed, the GFCI keeps the circuit shut off and will not reset.