Patent ID: 7525777

Claim:
A fireguard circuit for use as a safety device for a power cable, said power cable connecting a power source with a load, said power cable comprising a power line, a neutral line and a metal sheath which surrounds the power line and the neutral line, said fireguard circuit comprising: (a) a circuit breaker comprising a first switch located in one of said lines between the power source and the load, said switch having a first position in which the power source in its associated line is connected to the load and a second position in which the power source in its associated line is not connected to the load, (b) a circuit opening device for setting said switch in either its first position or its second position, said circuit opening device being operable in either a first state or a second state, said circuit opening device setting said switch in its first position when in its first state and said circuit opening device setting said switch in its second position when in its second state, (c) a first silicon controlled rectifier (SCR) for detecting the presence of an arcing condition between one of said lines and the metal sheath, said first SCR setting said circuit opening device at its second state upon detecting the presence of an arcing condition between one of said lines and the metal sheath, said first SCR comprising an anode, a cathode and a gate, (d) a second silicon controlled rectifier (SCR) for detecting the presence of an arcing condition between the other of said lines and the metal sheath, said second SCR setting said circuit opening device at its second state upon detecting the presence of an arcing condition between the other of said lines and the metal sheath, said second SCR comprising an anode, a cathode and a gate, and (e) a transistor circuit connected to the gate of said second SCR to reduce the peak voltage at which the metal sheath biases.