Test circuit for an AFCI/GFCI circuit breaker

A method of testing a circuit breaker, comprising the steps of:

• providing a circuit breaker coupled to at least first and second conductors for carrying load current between a source and a load, and having at least one series breaking element for interrupting the flow of current to the load;
• providing at least a first current sensor having an output coupled to the circuit breaker, the at least first and second conductors being coupled to the first current sensor for sensing the net current carried on the at least first and second conductors;
• including in the first current sensor a shunt connected at each end to the first conductor for bypassing a small portion of the load current around the first current sensor to unbalance the net flux producing an output of the current sensor, thereby increasing the detection sensitivity of the current sensor to a test current coupled in series with one of the first and second conductors;
• injecting from a waveform generator connected to the one of the first and second conductors a waveform including a test current into one of the first and second conductors during a test operation wherein the other of the one of the first and second mains conductors is open circuited;
• detecting the test current with a control circuit;
• and
• providing an indication responsive to the test current.

A test circuit for testing a circuit breaker, comprising:

• a circuit breaker under test, said circuit breaker including:
• first and second mains conductors coupleable to a power line;
• a control circuit for operating the circuit breaker in the presence of a fault current in said mains conductors;
• wherein
• said control circuit is operatively responsive to a shunted current sensor coupled to said mains conductors wherein a shunt portion of said shunted current sensor is coupled at each end to a select one of said mains conductors and bypasses only a small fraction of current flowing in said select one of said mains conductors;
• a waveform generator for injecting a test signal in series with one of said mains conductors wherein said test signal includes a smaller replica of an expected actual fault current;
• and
• a power source for supplying operating voltages to said circuit breaker.

A circuit for testing an electronic circuit breaker having line and neutral conductors coupleable in series with the line and neutral conductors of a power line and having a control circuit for operating separable contacts in at least one of said line and neutral conductors, comprising:

• a differential sensor responsive to currents flowing in said line and neutral conductors and having an output coupled to an input of said control circuit in said circuit breaker;
• a power source coupled to said circuit breaker for providing operating voltages thereto;
• and
• a waveform interface circuit for coupling one or more test waveforms from a source external to said circuit breaker to one of said line and neutral conductors wherein a portion of a first one of said test waveforms coupled by said interface circuit includes a coded signal for preconfiguring said circuit breaker for testing.