Frequency-dependent ground fault circuit interrupter

A method that comprises:

• receiving a signal current from a current transformer configured to sense a net current through multiple power conductors;
• converting the signal current into a frequency-dependent signal voltage, the frequency-dependent signal voltage being smaller for higher frequencies than for lower frequencies;
• deriving a magnitude measurement from the signal voltage;
• and
• interrupting at least one of the multiple power conductors when the magnitude measurement exceeds a frequency-independent and/or phase-independent threshold for a predetermined period of time or a predetermined number of times.

A circuit that comprises:

• an operational amplifier having an inverting input coupled to a current transformer configured to sense a net current through multiple power conductors, the operational amplifier having an output coupled to the inverting input via a feedback impedance that decreases with frequency;
• a comparator configured to produce a comparator signal indicating when the output of the operational amplifier exceeds a frequency-independent value;
• a controller configured to compare measure a percentage of time that the comparator signal is asserted, the percentage measurement representing a magnitude of the output of the operational amplifier, the controller further configured to assert an interrupt signal when the percentage measurement indicates a ground fault;
• and
• a relay configured to interrupt at least one of the multiple power conductors when the interrupt signal is asserted.