The invention is directed to a method and a device for detecting fault current arcing in electric circuits for consumers with relatively constant power consumption, particularly in onboard aircraft power supplies. The object of the invention is to find a novel possibility for detecting arc faults in electric lines of consumers with a relatively constant power consumption which appreciably reduces erroneous triggering of safeguards without compromising the reliability of switching off in the event that arcing actually occurs. This object is met, according to the invention, in that a voltage value is measured simultaneous with the current measurement, a ratio is formed of the current measurement values and voltage measurement values that are detected in parallel, and an indicator signal is generated for detected arcing when changes in the ratio of current measurement values and voltage measurement values exceed a predetermined threshold value.