The invention relates to a system for protecting an electrical device that can be connected to an electrical conductor system, comprising a signal generator for generating a first signal in the conductor system, a detecting device for detecting a second signal, which is based on the first signal, in the conductor system, a determining device for determining physical properties of the conductor system on the basis of the first and the second signal, and a control device for limiting a functionality of the device in case the determined physical properties deviate from predetermined physical properties by more than a predetermined amount.