The invention relates to a method and to a device for shutting down an installation part provided with connected equipment in an ungrounded power supply system in case of an insulation fault in a direct-current circuit connected to the installation part to be shut down. The invention is based on first determining the insulation resistance of the IT power supply system and measuring the displacement direct voltage present in the IT power supply system and then determining by combined evaluation of the measured results if there is a risk of an disruptive influence on the operating behavior of the connected equipment due to the displacement direct voltage occurring during the duration of a predeterminable time interval. If a disruptive influence is to be expected, the installation part exhibiting the insulation fault is immediately shut down together with the direct-current circuit and the equipment connected thereto.