AC/DC-sensitive residual current circuit breakers type EPA RCCB B1 and RCCB B2 are intended for the use in 50 Hz AC systems with electronic equipment, such as frequency inverters, uninterruptible power supplies (UPS), switched-mode power supplies, phase angle controllers (soft starters), and thyristor controllers. Modern devices of power electronic, e. g. frequency inverters and AC/DC converters, produce a bipolar, pulse width modulated voltage at the output, which need to have switching frequencies in the range of up to 20 kHz. In case a failure occurs, these resources can cause in addition to 50 Hz AC and pulse DC residual currents also smooth DC residual currents and residual currents with mixed frequencies (in frequency inverters, e.g. the switching frequency and the output frequency). Commercially available residual current circuit breakers with tripping characteristic AC or A (according to IEC 60755) can not correctly capture such residual currents, so that a proper tripping of the residual current circuit breaker is not guaranteed.