Abstract: A system for detecting arcing faults in DC electrical cable power distribution circuits, typically in telecommunications networks, monitors the power spectrum of distribution lines over a frequency band of about 4 Hz to 5 KHz in which current surges characteristic of arcing line faults have been found to occur. The system compares power levels in this detection band with a threshold level typical of normal communications traffic and registers an alarm condition when an excess indicative of arcing is detected.

Abstract: A safety switch light fence for vehicles such as fork lift trucks has a photoelectric cell system positioned across a vehicle exit opening in an area where an operater's foot is disposed when the operator allows his foot to protrude from the cab. At least one of a signaling device and an automatic cut-off are activated when protrusion of an operator's leg or foot is sensed. One or more light beams are directed across the exit opening. A foot switch can be used to sense proper placement of the operator's feet in the cab and to disable the photoelectric cell system, alarm and/or cut-off if the feet are safely stowed.