Abstract: A protective device for electric loads coupled to power circuits, such as the ac power lines inside buildings, has a surge suppressor including a nonlinear surge-protective device in shunt with a resistor-capacitor damping network. This suppressor circuit is well coordinated with a suitable arrester connected to the power lines, for example at the point of entry of ac supply mains into the building. The arrester has a lower voltage protection level than the surge suppressor. This suppressor circuit limits transient voltages at the load and also damps the oscillatory surges that occur in a power connection as described.

Abstract: Overvoltage protection devices operative to prevent damage to electrical equipment in response to overvoltages in the form of fast transients and also to continuous overvoltages utilizes clamping or discharge elements which conduct in response to overvoltages or current surges. A high voltage responsive element, suitably a spark gap, is connected to the input of the device which goes to the line, while a lower voltage responsive element, suitably an avalanche diode or diodes or a zener diode or diodes, is connected to the output of the device which goes to the equipment to be protected. A resistor is connected between the spark gap and the avalanche device in series with one side of the line on the circuit to be protected.

Abstract: A lightning activated relay utilizes an electric or magnetic field responsive detector for determining the presence of atmospheric conditions potentially capable of producing lightning or for detecting the occurrence of lightning within a predetermined range. Switching circuitry responsive to the detector is provided for isolating electrical equipment from the electric power mains and isolating or grounding communications or other equipment susceptible to lightning damage when such conditions are detected or upon the occurrence of a temporary power interruption.