Line voltage pulses from an upstream series arc fault are passed through a high pass filter. The filtered output is rectified and used to pulse-charge a capacitor. When the capacitor charge reaches a predetermined threshold, a first switch is activated, which in turn activates an SCR to trigger a circuit...http://www.google.com/patents/US6628487?utm_source=gb-gplus-sharePatent US6628487 - Method and apparatus for detecting upstream series arc faults
