Self testing circuit breaker ground fault and sputtering arc trip unit

A trip unit for a circuit breaker in a protected electrical system having a line conductor and a neutral conductor and subject to sputtering arc faults and ground faults, comprising:

• sensing coil means sensing currents in said protected electrical system, fault detector means connected to the sensing coil means for generating a trip signal in response to ground faults including grounded neutral faults and to sputtering arc faults, test means connected to said sensing coil means selectively injecting signals simulating grounded neutral and sputtering arc fault conditions into said fault detector means, said test means comprising a test conductor extending through said sensing coil means, a test switch for selectively connecting said test conductor in a closed loop extending through said sensing coil means, said test conductor having an impedance substantially equivalent to a maximum impedance of a grounded neutral fault in said protected electrical system, said sensing coil means comprising a first sensing coil through which both said line conductor and said neutral conductor pass and a second sensing coil through which said neutral conductor but not said line conductor passes, wherein said fault detection means comprises a dormant oscillator ground fault detector circuit connected to said first and second sensing coils and a sputtering arc detector circuit connected to said second sensing coil, wherein said test conductor means extends through both said first and second sensing coils, said second coil having a secondary winding, wherein said sputtering arc detection circuit comprises means connected to said secondary winding generating a bandwidth limited di/dt signal where i is current in said neutral conductor, and means responsive to said di/dt signal to generate said trip signal under preselected conditions, wherein said test means further comprises means injecting test signals into said secondary winding which cause said sputtering arc detector circuit to generate said trip signal.

A self testing trip unit for a circuit breaker in a protected electrical system having a line conductor and a neutral conductor and subject to sputtering arc faults, said trip unit comprising:

• a sensing coil having one of said line and neutral conductors as a primary winding and having a secondary winding;
• means connected to said secondary winding generating a bandwidth limited di/dt signal where i is current in said protected electrical system;
• level detector means comparing said bandwidth limited di/dt signal to a selected threshold;
• means generating a trip signal when said bandwidth limited di/dt signal exceeds said selected threshold a predetermined number of times in a selected interval;
• and test means connected to said sensing coil for generating pulses which produce a bandwidth limited di/dt signal which exceeds said selected threshold said predetermined number of times within said selected interval.