GFCI provides a dual function of personal ground fault and 3 mode surge protection. Conventional over-current protection devices such as fuses and circuit breakers cannot protect people from electrical shock or sensitive electronic equipment from momentary voltage & current surge. These devices are designed to disconnect the power when a current of several amperes flows through the circuit. However, a current as low as a few milliamperes can be dangerous to normal healthy human beings. One ampere equals 1000 milliamperes. Many electric shocks occur where the path of current flow is from the hot wire through the metal housing of a defective tool or appliance, through the body of a human being to ground. Because of the resistance of the human body to electrical current flow, the current will be quite low relative to that required to cause conventional over-current protection devices to function. However, it is likely to be high enough to cause a painful or possible lethal electric shock. Another important feature is that it protects not only the shock shield from voltage transients or surges, but also it protects the equipment that is plugged into the unit. Equipment is protected from line, neutral, and ground surge in 3 wire connected devices and line neutral surges in two wire connected devices. The GFCI that we sell are specification grade (industrial/commercial applications where reliability is critical). They are designed to trip at 5 MA in 1/30th of a second and they are UL-listed. With 1-3 receptacles, 15 amp, 120 volt AC.