A device for improving the filter effect of a filter connected up between an electrical energy source and a source of interference is provided. The filter is configured to feed back interference transients from ground to an input of the source of interference generating the interference transients. The device includes a measuring device for determining a leakage current flowing through the filter and a final control element configured to modify a limit frequency of the filter such that the leakage current through the filter is damped to below a predefined level if the measuring device detects the leakage current.