초록 ▼

A fireguard circuit for a power cable, which comprises a power line, a neutral line and a metal sheath surrounding the power line and the neutral line, includes a switch located in one of the lines. A solenoid sets the switch in either an open position or a closed position. A first silicon controll

A fireguard circuit for a power cable, which comprises a power line, a neutral line and a metal sheath surrounding the power line and the neutral line, includes a switch located in one of the lines. A solenoid sets the switch in either an open position or a closed position. A first silicon controlled rectifier (SCR) causes the solenoid to open the switch upon detecting the presence of an arcing condition between the power line and the metal sheath. A second silicon controlled rectifier (SCR) causes the solenoid to open the switch upon detecting the presence of an arcing condition between the neutral line and the metal sheath. The second SCR is connected in parallel with the first SCR, the anode of the first SCR being connected to the cathode of the second SCR and the cathode of the first SCR being connected to the anode of the second SCR.

대표청구항 ▼

What is claimed is: 1. 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 co

What is claimed is: 1. 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. 2. The fireguard circuit of claim 1 wherein said transistor circuit comprises a transistor, first, second and third resistors, a capacitor and a diode. 3. The fireguard circuit of claim 1 wherein the power connections for said circuit opening device and said first and second SCRs are derived from said power and neutral lines at the load. 4. The fireguard circuit of claim 1 wherein the power connections for said circuit opening device and said first and second SCRs are derived from said power and neutral lines at the power source. 5. 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, and (d) a diode bridge connecting the first SCR to the circuit opening device, the diode bridge acting to detect the presence of an arcing condition between the other of said lines and the metal sheath, said diode bridge 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. 6. The fireguard circuit of claim 5 wherein the power connections for said circuit opening device, said first SCR and said diode bridge are derived from said power and neutral lines at the load. 7. The fireguard circuit of claim 5 wherein the power connections for said circuit opening device, said first SCR and said diode bridge are derived from said power and neutral lines at the power source. 8. 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 zener diode connected in series to the metal sheath to reduce voltage bias in the metal sheath. 9. The fireguard circuit of claim 8 wherein said zener diode includes an anode and a cathode, the cathode of said zener diode being connected to the metal sheath.