Type A switches are sensitive to pulsating and alternating currents. This function is independent of the mains voltage.
Type AC switches only detect AC residual currents. As a result, in Germany they are not approved as residual current operated protective devices.
Type B switches are AC-DC sensitive at frequencies of 0 Hz (smooth residual currents) to 150 kHz. They have increased resistance to surge currents and lightning.
Type B+ residual current circuit-breakers detect smooth DC residual currents and all other residual currents at frequencies up to 20,000 Hz. The operating voltage required for this is taken from the mains supply. Correct power supply is ensured when the voltage between the mains conductors is ≥ 50 V. Pulsating and AC residual currents are detected independent of the mains voltage.
Type F switches are mixed frequency sensitive. They protect against pulsating and AC residual currents as well as residual currents with mixed frequencies that differ from 50 Hz independent of the mains voltage.