 Welcome to the video, Ground Fault Circuit Interruptors. Each year, hundreds of people die in the United States from household electrocutions. A radio falling into a bathtub is just one example of how an electrocution can occur. As the water enters the interior of the submerged radio, the water makes contact with one of the radio's hot wires. Current flows into the water through the bather to the drain and into the ground. The current may be high enough to be fatal. To protect people from being electrocuted, Ground Fault Circuit Interruptors GFCI were developed for locations in the home where potential hazardous conditions can occur. Before the introduction of GFCIs in newly constructed homes, 700 people died from household electrocutions nationally each year. As of 2001, that number has decreased to about 400 deaths each year, according to the Electrical Safety Foundation. Most GFCIs are built into the housing of an electrical receptacle. They are installed in areas that are potentially dangerous, such as bathrooms. Here is a typical circuit configuration of a GFCI. Alternating current flows to the load through the hot wire labeled L1 and the neutral wire labeled N. Under normal conditions, the current flow through L1 and N should be the same. Both conductors L1 and N are located inside a sensor, which is connected to solid state circuitry. As long as the current in the conductors is equal, electrical power will be supplied to the load. However, if one of the connectors comes in contact with an object that is grounded, either directly or through a person's body, the GFCI in the receptacle will immediately open the circuit and stop current flow. Under normal conditions, 5 amps flow through the conductors L and N. Inside the receptacle, both conductors are located inside the ring of a toroidal transformer. During the positive alternation, current flows through one conductor in a given direction and in the opposite direction through the other conductor. During the negative alternation, the current through the conductor reverses. Following the left hand rule, the direction of the flux lines that form around the conductors is determined by the direction of the electron flow. During the positive alternation, the magnetic fields of the conductor on the left induce flux lines into the ring of a toroidal transformer in one direction. The magnetic field of the conductor on the right induces flux lines into the toroidal ring in the opposite direction. The result is that the flux lines completely cancel each other. During the negative alternation, the magnetic field of the conductor on the left induces flux lines in the ring in a counterclockwise direction. The magnetic field of the conductor on the right induces flux lines into the ring in a clockwise direction. Again, the result is that the flux lines completely cancel. Let's suppose a person comes in contact with conductor L1. An alternate path for current is created. Assume that 0.005 amps, or 5 milliamps, flows to the ground through the person and the remainder of the 5 amps of the power source, 4.995 amps, flows through conductor N. When this condition occurs, the magnetic field around the conductor on the left is a little weaker than the field around the conductor on the right. The result is that the flux lines induced into the ring by the conductor on the left weaken, while the strength of the flux lines induced by the conductor on the right remains unchanged. The flux lines on the left portion of the ring are not able to completely cancel the flux lines induced by the conductor on the right. Therefore, the flux lines that were not cancelled are strong enough to induce a voltage into the coil wrapped around the ring. The voltage that is developed by the coil is applied to the solid state circuitry, activating the circuit breaker mechanism that opens line L1 and N. First, the current travels through the body. Secondly, the current transformer senses the imbalance. Thirdly, the sensor opens the circuit. GFCIs are activated by a difference of currents of 5 mil amps between lines L1 and N. Once the GFCI has been tripped, it must be reset before the receptacle can be re-energized. Pushing a reset button reconnects the circuit breaker contacts. It is recommended that the GFCI be checked periodically to be sure it is operating properly. Pressing the test button which causes the GFCI to trip performs this procedure. When the button is pressed, current flows through the branch circuit from L1 to line N through a current limiting resistor. The wire between L1 and the test button goes through the toroidal ring. However, the wire between line N and the push button is not located inside the ring. A voltage is developed at the coil and causes the breaker to trip because flux lines from line N do not cancel the flux lines in the ring from the L1 wire. Congratulations! You've completed the video Ground Fault Circuit Interruptors.