Fireguard circuit

A fireguard circuit for use with 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) an indicator circuit connected to said power and neutral lines at said load, said indicator circuit providing an indication as to whether power is being applied to said load.

A fireguard circuit for use with 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 to said second SCR to reduce the peak voltage at which the metal sheath biases.

A fireguard circuit for use with 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 said second SCR to reduce the peak voltage at which the metal sheath biases.

A fireguard circuit for use with 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 for detecting 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.

A fireguard circuit for use with 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 zener diode connected to the metal sheath to reduce voltage bias in the metal sheath.

A fireguard circuit for use with 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 first bias resistor for reducing voltage bias in the metal sheath, said first bias resistor comprising a first terminal connected to one of said lines and a second terminal connected to the metal sheath.

A fireguard circuit for use with 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 test circuit connected to one of said lines to ensure proper operation of said fireguard circuit.

A fireguard circuit for use with 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 and a second switch, the first switch being located in the power line between the power source and the load, the second switch being located in the neutral line between the power source and the load, each of said first and second switches 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 each of said first and second switches 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 each of said switches in its first position when in its first state and said circuit opening device setting each of said switches in its second position when in its second state, the power connection for said circuit opening device being derived from the power line at the power source,
• (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, the power connection for said first SCR being derived from the neutral lines at the power source, and
• (d) a third switch located in the line between said circuit opening device and the power line at the power source, the third switch having a first position in which the power source is connected to said circuit opening device and a second position in which the power source is not connected to said circuit opening device, said circuit opening device setting said third switch in its first position when in its first state and said circuit opening device setting said third switch in its second position when in its second state.

A fireguard circuit for use with 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 and a second switch, the first switch being located in the power line between the power source and the load, the second switch being located in the neutral line between the power source and the load, each of said first and second switches 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 each of said first and second switches 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 each of said switches in its first position when in its first state and said circuit opening device setting each of said switches in its second position when in its second state, the power connection for said circuit opening device being derived from the power line at the power source,
• (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, the power connection for said first SCR being derived from the neutral lines at the power source, and
• (d) a capacitor and a resistor connected in series, the free end of the capacitor being connected to the anode of the first SCR and the free end of the resistor being connected to the cathode of the first SCR.

A fireguard circuit for use with a power cable, said power cable connecting a power source with a load, said power cable comprising first and second lines as in a 240 volt system and a metal sheath, the metal sheath surrounding both the first and second lines, the fireguard circuit being connected between the first and second lines, 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, the first 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 the first 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 first switch in its first position when in its first state and said circuit opening device setting said first switch in its second position when in its second state, and
• (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.