Residual current transformers with characteristic B+ detect pulsating and smooth DC residual currents as well as AC residual currents up to 100 kHz. The residual current transformer covers all of the active conductors leading to the consumers. It uses the conductor currents flowing through it (outgoing and returning) to illustrate the difference in the form of direct voltage. The direct voltage value depends on the residual current value, the set residual current range of the evaluation unit and the frequency range of the residual current.