Our GFCI outlet will automatically perform a self-test every 40 seconds (the red light will flash once) to ensure that the GFCI continues to work, which is very suitable for use in homes, offices, hospitals, schools, etc. Our GFCI receptacles with usb are made of high-quality thermoplastic materials, with a reasonable structural design to ensure excellent strength and durability, and provide continuous ground fault protection. Even when performing self-test, it can detect the actual ground fault and trip Our GFCI socket with usb has an LED indicator light. If the indicator light is green, it means that you have installed the GFCI socket correctly and is working normally. When the GFCI socket reaches the end of its service life, the red indicator light will light up to remind you to replace the socket in time Our GFCI receptacle is suitable for 12 or 14AWG wires of side wire and back wire, which can be easily installed in any electrical box, and can prevent reverse wiring of line