Arc Fault Detection Devices (AFDD/AFCI ): hereinafter referred to as the protector, effectively detects the fault arc in the access line, including the fault parallel arc and the fault series arc, and when the fault arc that causes fire is detected in the line, the power off function can be carried out to achieve the purpose of early warning of fire. The fault arc protector is suitable for electrical circuits of 10KW and below in industrial and civil buildings